Scanner Package In Java | Hàm Tạo Của Lớp Scanner Trong Java

Java Scanner import

Input Types

In the example above, we used the

nextLine()

method, which is used to read Strings. To read other types, look at the table below:

Method	Description
Reads a
Reads a
Reads a
Reads a
Reads a
Reads a
Reads a
Reads a

In the example below, we use different methods to read data of various types:

Example


import java.util.Scanner; class Main { public static void main(String[] args) { Scanner myObj = new Scanner(System.in); System.out.println("Enter name, age and salary:"); // String input String name = myObj.nextLine(); // Numerical input int age = myObj.nextInt(); double salary = myObj.nextDouble(); // Output input by user System.out.println("Name: " + name); System.out.println("Age: " + age); System.out.println("Salary: " + salary); } }


Note: If you enter wrong input (e.g. text in a numerical input), you will get an exception/error message (like “InputMismatchException”).

You can read more about exceptions and how to handle errors in the Exceptions chapter.

What happens if you don’t import the Scanner?

If you attempt to use the Scanner class but fail to add an import, or don’t explicitly reference the package and the class together, you will encounter the following error:

Error: Scanner cannot be resolved to a type

The “cannot be resolved to a type” compile time error may sound somewhat confusing to a new developer. All it’s saying is that you have referenced a class that is outside of any package referenced through an import statement.

If you get the “Scanner cannot be resolved to a type” error message, just add the Java Scanner import statement to your code, or explicitly reference the package when you use the Scanner class in your code.

public final class Scanner extends Object implements Iterator

, Closeable

A

Scanner

breaks its input into tokens using a
delimiter pattern, which by default matches whitespace. The resulting
tokens may then be converted into values of different types using the
various next methods.

For example, this code allows a user to read a number from System.in:


Scanner sc = new Scanner(System.in); int i = sc.nextInt();


As another example, this code allows

long

types to be
assigned from entries in a file

myNumbers

:


Scanner sc = new Scanner(new File("myNumbers")); while (sc.hasNextLong()) { long aLong = sc.nextLong(); }


The scanner can also use delimiters other than whitespace. This example reads several items in from a string:


String input = "1 fish 2 fish red fish blue fish"; Scanner s = new Scanner(input).useDelimiter("\\s*fish\\s*"); System.out.println(s.nextInt()); System.out.println(s.nextInt()); System.out.println(s.next()); System.out.println(s.next()); s.close();


prints the following output:


1 2 red blue


The same output can be generated with this code, which uses a regular expression to parse all four tokens at once:


String input = "1 fish 2 fish red fish blue fish"; Scanner s = new Scanner(input); s.findInLine("(\\d+) fish (\\d+) fish (\\w+) fish (\\w+)"); MatchResult result = s.match(); for (int i=1; i<=result.groupCount(); i++) System.out.println(result.group(i)); s.close();


The default whitespace delimiter used
by a scanner is as recognized by

Character

.

isWhitespace

. The

reset()

method will reset the value of the scanner’s delimiter to the default
whitespace delimiter regardless of whether it was previously changed.

A scanning operation may block waiting for input.

The

next()

and

hasNext()

methods and their
primitive-type companion methods (such as

nextInt()

and

hasNextInt()

) first skip any input that matches the delimiter
pattern, and then attempt to return the next token. Both hasNext
and next methods may block waiting for further input. Whether a
hasNext method blocks has no connection to whether or not its
associated next method will block.

The

findInLine(java.lang.String)

,

findWithinHorizon(java.lang.String, int)

, and

skip(java.util.regex.Pattern)

methods operate independently of the delimiter pattern. These methods will
attempt to match the specified pattern with no regard to delimiters in the
input and thus can be used in special circumstances where delimiters are
not relevant. These methods may block waiting for more input.

When a scanner throws an

InputMismatchException

, the scanner
will not pass the token that caused the exception, so that it may be
retrieved or skipped via some other method.

Depending upon the type of delimiting pattern, empty tokens may be returned. For example, the pattern “\\s+” will return no empty tokens since it matches multiple instances of the delimiter. The delimiting pattern “\\s” could return empty tokens since it only passes one space at a time.

A scanner can read text from any object which implements the

Readable

interface. If an invocation of the underlying
readable’s

Readable.read(java.nio.CharBuffer)

method throws an

IOException

then the scanner assumes that the end of the input
has been reached. The most recent IOException thrown by the
underlying readable can be retrieved via the

ioException()

method.

When a

Scanner

is closed, it will close its input source
if the source implements the

Closeable

interface.

A

Scanner

is not safe for multithreaded use without
external synchronization.

Unless otherwise mentioned, passing a

null

parameter into
any method of a

Scanner

will cause a

NullPointerException

to be thrown.

A scanner will default to interpreting numbers as decimal unless a
different radix has been set by using the

useRadix(int)

method. The

reset()

method will reset the value of the scanner’s radix to

10

regardless of whether it was previously changed.

An instance of this class is capable of scanning numbers in the standard
formats as well as in the formats of the scanner’s locale. A scanner’s
initial locale is the value returned by the

Locale.getDefault(Locale.Category.FORMAT)

method; it may be changed via the

useLocale(java.util.Locale)

method. The

reset()

method will reset the value of the
scanner’s locale to the initial locale regardless of whether it was
previously changed.

The localized formats are defined in terms of the following parameters,
which for a particular locale are taken from that locale’s

DecimalFormat

object, df, and its and

DecimalFormatSymbols

object,
dfs.

LocalGroupSeparator


The character used to separate thousands groups, i.e., dfs.


getGroupingSeparator()


LocalDecimalSeparator


The character used for the decimal point, i.e., dfs.


getDecimalSeparator()


LocalPositivePrefix


The string that appears before a positive number (may be empty), i.e., df.


getPositivePrefix()


LocalPositiveSuffix


The string that appears after a positive number (may be empty), i.e., df.


getPositiveSuffix()


LocalNegativePrefix


The string that appears before a negative number (may be empty), i.e., df.


getNegativePrefix()


LocalNegativeSuffix


The string that appears after a negative number (may be empty), i.e., df.


getNegativeSuffix()


LocalNaN


The string that represents not-a-number for floating-point values, i.e., dfs.


getNaN()


LocalInfinity


The string that represents infinity for floating-point values, i.e., dfs.


getInfinity()


The strings that can be parsed as numbers by an instance of this class are specified in terms of the following regular-expression grammar, where Rmax is the highest digit in the radix being used (for example, Rmax is 9 in base 10).


Character.isDigit(c) returns true


Whitespace is not significant in the above regular expressions.

Constructor and Description

Constructs a new

Constructs a new

Constructs a new

Constructs a new

Constructs a new

Constructs a new

Constructs a new

Constructs a new

Constructs a new

Constructs a new

Modifier and Type	Method and Description
Closes this scanner.
Returns the
Attempts to find the next occurrence of the specified pattern ignoring delimiters.
Attempts to find the next occurrence of a pattern constructed from the specified string, ignoring delimiters.
Attempts to find the next occurrence of the specified pattern.
Attempts to find the next occurrence of a pattern constructed from the specified string, ignoring delimiters.
Returns true if this scanner has another token in its input.
Returns true if the next complete token matches the specified pattern.
Returns true if the next token matches the pattern constructed from the specified string.
Returns true if the next token in this scanner’s input can be interpreted as a
Returns true if the next token in this scanner’s input can be interpreted as a
Returns true if the next token in this scanner’s input can be interpreted as a
Returns true if the next token in this scanner’s input can be interpreted as a boolean value using a case insensitive pattern created from the string “true|false”.
Returns true if the next token in this scanner’s input can be interpreted as a byte value in the default radix using the
Returns true if the next token in this scanner’s input can be interpreted as a byte value in the specified radix using the
Returns true if the next token in this scanner’s input can be interpreted as a double value using the
Returns true if the next token in this scanner’s input can be interpreted as a float value using the
Returns true if the next token in this scanner’s input can be interpreted as an int value in the default radix using the
Returns true if the next token in this scanner’s input can be interpreted as an int value in the specified radix using the
Returns true if there is another line in the input of this scanner.
Returns true if the next token in this scanner’s input can be interpreted as a long value in the default radix using the
Returns true if the next token in this scanner’s input can be interpreted as a long value in the specified radix using the
Returns true if the next token in this scanner’s input can be interpreted as a short value in the default radix using the
Returns true if the next token in this scanner’s input can be interpreted as a short value in the specified radix using the
Returns the
Returns this scanner’s locale.
Returns the match result of the last scanning operation performed by this scanner.
Finds and returns the next complete token from this scanner.
Returns the next token if it matches the specified pattern.
Returns the next token if it matches the pattern constructed from the specified string.
Scans the next token of the input as a
Scans the next token of the input as a
Scans the next token of the input as a
Scans the next token of the input into a boolean value and returns that value.
Scans the next token of the input as a byte.
Scans the next token of the input as a byte.
Scans the next token of the input as a double.
Scans the next token of the input as a float.
Scans the next token of the input as an int.
Scans the next token of the input as an int.
Advances this scanner past the current line and returns the input that was skipped.
Scans the next token of the input as a long.
Scans the next token of the input as a long.
Scans the next token of the input as a short.
Scans the next token of the input as a short.
Returns this scanner’s default radix.
The remove operation is not supported by this implementation of
Resets this scanner.
Skips input that matches the specified pattern, ignoring delimiters.
Skips input that matches a pattern constructed from the specified string.
Returns the string representation of this
Sets this scanner’s delimiting pattern to the specified pattern.
Sets this scanner’s delimiting pattern to a pattern constructed from the specified
Sets this scanner’s locale to the specified locale.
Sets this scanner’s default radix to the specified radix.


clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait


forEachRemaining


public Scanner(Readable source)


Scannerthat produces values scanned from the specified source.


source- A character source implementing the


Readableinterface


public Scanner(InputStream source)


Scannerthat produces values scanned from the specified input stream. Bytes from the stream are converted into characters using the underlying platform's default charset.


source- An input stream to be scanned


public Scanner(InputStream source, String charsetName)


Scannerthat produces values scanned from the specified input stream. Bytes from the stream are converted into characters using the specified charset.


source- An input stream to be scanned


charsetName- The encoding type used to convert bytes from the stream into characters to be scanned


IllegalArgumentException- if the specified character set does not exist


public Scanner(File source) throws FileNotFoundException


Scannerthat produces values scanned from the specified file. Bytes from the file are converted into characters using the underlying platform's default charset.


source- A file to be scanned


FileNotFoundException- if source is not found


public Scanner(File source, String charsetName) throws FileNotFoundException


Scannerthat produces values scanned from the specified file. Bytes from the file are converted into characters using the specified charset.


source- A file to be scanned


charsetName- The encoding type used to convert bytes from the file into characters to be scanned


FileNotFoundException- if source is not found


IllegalArgumentException- if the specified encoding is not found


public Scanner(Path source) throws IOException


Scannerthat produces values scanned from the specified file. Bytes from the file are converted into characters using the underlying platform's default charset.


source- the path to the file to be scanned


IOException- if an I/O error occurs opening source


public Scanner(Path source, String charsetName) throws IOException


Scannerthat produces values scanned from the specified file. Bytes from the file are converted into characters using the specified charset.


source- the path to the file to be scanned


charsetName- The encoding type used to convert bytes from the file into characters to be scanned


IOException- if an I/O error occurs opening source


IllegalArgumentException- if the specified encoding is not found


public Scanner(String source)


Scannerthat produces values scanned from the specified string.


source- A string to scan


public Scanner(ReadableByteChannel source)


Scannerthat produces values scanned from the specified channel. Bytes from the source are converted into characters using the underlying platform's default charset.


source- A channel to scan


public Scanner(ReadableByteChannel source, String charsetName)


Scannerthat produces values scanned from the specified channel. Bytes from the source are converted into characters using the specified charset.


source- A channel to scan


charsetName- The encoding type used to convert bytes from the channel into characters to be scanned


IllegalArgumentException- if the specified character set does not exist


public void close()

If this scanner has not yet been closed then if its underlying
readable also implements the

Closeable

interface then the readable’s close method
will be invoked. If this scanner is already closed then invoking this
method will have no effect.

Attempting to perform search operations after a scanner has
been closed will result in an

IllegalStateException

.


closein interface


Closeable


closein interface


AutoCloseable


public IOException ioException()


IOExceptionlast thrown by this


Scanner's underlying


Readable. This method returns


nullif no such exception exists.


public Pattern delimiter()


Patternthis


Scanneris currently using to match delimiters.


public Scanner useDelimiter(Pattern pattern)


pattern- A delimiting pattern


public Scanner useDelimiter(String pattern)


String.


An invocation of this method of the form useDelimiter(pattern) behaves in exactly the same way as the invocation useDelimiter(Pattern.compile(pattern)).

Invoking the

reset()

method will set the scanner’s delimiter
to the default.


pattern- A string specifying a delimiting pattern


public Locale locale()

A scanner’s locale affects many elements of its default primitive matching regular expressions; see localized numbers above.

public Scanner useLocale(Locale locale)

A scanner’s locale affects many elements of its default primitive matching regular expressions; see localized numbers above.

Invoking the

reset()

method will set the scanner’s locale to
the initial locale.


locale- A string specifying the locale to use


public int radix()

A scanner’s radix affects elements of its default number matching regular expressions; see localized numbers above.

public Scanner useRadix(int radix)

A scanner’s radix affects elements of its default number matching regular expressions; see localized numbers above.

If the radix is less than

Character.MIN_RADIX

or greater than

Character.MAX_RADIX

, then an

IllegalArgumentException

is thrown.

Invoking the

reset()

method will set the scanner’s radix to

10

.


radix- The radix to use when scanning numbers


IllegalArgumentException- if radix is out of range


public MatchResult match()


IllegalStateExceptionif no match has been performed, or if the last match was not successful.


The various

next

methods of

Scanner

make a match result available if they complete without throwing an
exception. For instance, after an invocation of the

nextInt()

method that returned an int, this method returns a

MatchResult

for the search of the
Integer regular expression
defined above. Similarly the

findInLine(java.lang.String)

,

findWithinHorizon(java.lang.String, int)

, and

skip(java.util.regex.Pattern)

methods will make a
match available if they succeed.


IllegalStateException- If no match result is available


public String toString()

Returns the string representation of this

Scanner

. The
string representation of a

Scanner

contains information
that may be useful for debugging. The exact format is unspecified.

public boolean hasNext()


hasNextin interface


Iterator


IllegalStateException- if this scanner is closed


Iterator


public String next()


hasNext()returned


true.


nextin interface


Iterator


NoSuchElementException- if no more tokens are available


IllegalStateException- if this scanner is closed


Iterator


public void remove()


Iterator.


removein interface


Iterator


UnsupportedOperationException- if this method is invoked.


Iterator


public boolean hasNext(String pattern)

An invocation of this method of the form hasNext(pattern) behaves in exactly the same way as the invocation hasNext(Pattern.compile(pattern)).


pattern- a string specifying the pattern to scan


IllegalStateException- if this scanner is closed


public String next(String pattern)

An invocation of this method of the form next(pattern) behaves in exactly the same way as the invocation next(Pattern.compile(pattern)).


pattern- a string specifying the pattern to scan


NoSuchElementException- if no such tokens are available


IllegalStateException- if this scanner is closed


public boolean hasNext(Pattern pattern)


pattern- the pattern to scan for


IllegalStateException- if this scanner is closed


public String next(Pattern pattern)


hasNext(Pattern)returned


true. If the match is successful, the scanner advances past the input that matched the pattern.


pattern- the pattern to scan for


NoSuchElementException- if no more tokens are available


IllegalStateException- if this scanner is closed


public boolean hasNextLine()


IllegalStateException- if this scanner is closed


public String nextLine()

Since this method continues to search through the input looking for a line separator, it may buffer all of the input searching for the line to skip if no line separators are present.


NoSuchElementException- if no line was found


IllegalStateException- if this scanner is closed


public String findInLine(String pattern)

An invocation of this method of the form findInLine(pattern) behaves in exactly the same way as the invocation findInLine(Pattern.compile(pattern)).


pattern- a string specifying the pattern to search for


IllegalStateException- if this scanner is closed


public String findInLine(Pattern pattern)


nullis returned and the scanner's position is unchanged. This method may block waiting for input that matches the pattern.


Since this method continues to search through the input looking for the specified pattern, it may buffer all of the input searching for the desired token if no line separators are present.


pattern- the pattern to scan for


IllegalStateException- if this scanner is closed


public String findWithinHorizon(String pattern, int horizon)

An invocation of this method of the form findWithinHorizon(pattern) behaves in exactly the same way as the invocation findWithinHorizon(Pattern.compile(pattern, horizon)).


pattern- a string specifying the pattern to search for


horizon- the search horizon


IllegalStateException- if this scanner is closed


IllegalArgumentException- if horizon is negative


public String findWithinHorizon(Pattern pattern, int horizon)

This method searches through the input up to the specified search horizon, ignoring delimiters. If the pattern is found the scanner advances past the input that matched and returns the string that matched the pattern. If no such pattern is detected then the null is returned and the scanner’s position remains unchanged. This method may block waiting for input that matches the pattern.

A scanner will never search more than

horizon

code
points beyond its current position. Note that a match may be clipped
by the horizon; that is, an arbitrary match result may have been
different if the horizon had been larger. The scanner treats the
horizon as a transparent, non-anchoring bound (see

Matcher.useTransparentBounds(boolean)

and

Matcher.useAnchoringBounds(boolean)

).

If horizon is , then the horizon is ignored and
this method continues to search through the input looking for the
specified pattern without bound. In this case it may buffer all of
the input searching for the pattern.

If horizon is negative, then an IllegalArgumentException is thrown.


pattern- the pattern to scan for


horizon- the search horizon


IllegalStateException- if this scanner is closed


IllegalArgumentException- if horizon is negative


public Scanner skip(Pattern pattern)

If a match to the specified pattern is not found at the current position, then no input is skipped and a NoSuchElementException is thrown.

Since this method seeks to match the specified pattern starting at the scanner’s current position, patterns that can match a lot of input (“.*”, for example) may cause the scanner to buffer a large amount of input.

Note that it is possible to skip something without risking a

NoSuchElementException

by using a pattern that can
match nothing, e.g.,

sc.skip("[ \t]*")

.


pattern- a string specifying the pattern to skip over


NoSuchElementException- if the specified pattern is not found


IllegalStateException- if this scanner is closed


public Scanner skip(String pattern)

An invocation of this method of the form skip(pattern) behaves in exactly the same way as the invocation skip(Pattern.compile(pattern)).


pattern- a string specifying the pattern to skip over


IllegalStateException- if this scanner is closed


public boolean hasNextBoolean()


IllegalStateException- if this scanner is closed


public boolean nextBoolean()


InputMismatchExceptionif the next token cannot be translated into a valid boolean value. If the match is successful, the scanner advances past the input that matched.


InputMismatchException- if the next token is not a valid boolean


NoSuchElementException- if input is exhausted


IllegalStateException- if this scanner is closed


public boolean hasNextByte()


nextByte()method. The scanner does not advance past any input.


IllegalStateException- if this scanner is closed


public boolean hasNextByte(int radix)


nextByte()method. The scanner does not advance past any input.


radix- the radix used to interpret the token as a byte value


IllegalStateException- if this scanner is closed


public byte nextByte()

An invocation of this method of the form
nextByte() behaves in exactly the same way as the
invocation nextByte(radix), where

radix

is the default radix of this scanner.


InputMismatchException- if the next token does not match the Integer regular expression, or is out of range


NoSuchElementException- if input is exhausted


IllegalStateException- if this scanner is closed


public byte nextByte(int radix)


InputMismatchExceptionif the next token cannot be translated into a valid byte value as described below. If the translation is successful, the scanner advances past the input that matched.


If the next token matches the Integer regular expression defined
above then the token is converted into a byte value as if by
removing all locale specific prefixes, group separators, and locale
specific suffixes, then mapping non-ASCII digits into ASCII
digits via

Character.digit

, prepending a
negative sign (-) if the locale specific negative prefixes and suffixes
were present, and passing the resulting string to

Byte.parseByte

with the
specified radix.


radix- the radix used to interpret the token as a byte value


InputMismatchException- if the next token does not match the Integer regular expression, or is out of range


NoSuchElementException- if input is exhausted


IllegalStateException- if this scanner is closed


public boolean hasNextShort()


nextShort()method. The scanner does not advance past any input.


IllegalStateException- if this scanner is closed


public boolean hasNextShort(int radix)


nextShort()method. The scanner does not advance past any input.


radix- the radix used to interpret the token as a short value


IllegalStateException- if this scanner is closed


public short nextShort()

An invocation of this method of the form
nextShort() behaves in exactly the same way as the
invocation nextShort(radix), where

radix

is the default radix of this scanner.


InputMismatchException- if the next token does not match the Integer regular expression, or is out of range


NoSuchElementException- if input is exhausted


IllegalStateException- if this scanner is closed


public short nextShort(int radix)


InputMismatchExceptionif the next token cannot be translated into a valid short value as described below. If the translation is successful, the scanner advances past the input that matched.


If the next token matches the Integer regular expression defined
above then the token is converted into a short value as if by
removing all locale specific prefixes, group separators, and locale
specific suffixes, then mapping non-ASCII digits into ASCII
digits via

Character.digit

, prepending a
negative sign (-) if the locale specific negative prefixes and suffixes
were present, and passing the resulting string to

Short.parseShort

with the
specified radix.


radix- the radix used to interpret the token as a short value


InputMismatchException- if the next token does not match the Integer regular expression, or is out of range


NoSuchElementException- if input is exhausted


IllegalStateException- if this scanner is closed


public boolean hasNextInt()


nextInt()method. The scanner does not advance past any input.


IllegalStateException- if this scanner is closed


public boolean hasNextInt(int radix)


nextInt()method. The scanner does not advance past any input.


radix- the radix used to interpret the token as an int value


IllegalStateException- if this scanner is closed


public int nextInt()

An invocation of this method of the form
nextInt() behaves in exactly the same way as the
invocation nextInt(radix), where

radix

is the default radix of this scanner.


InputMismatchException- if the next token does not match the Integer regular expression, or is out of range


NoSuchElementException- if input is exhausted


IllegalStateException- if this scanner is closed


public int nextInt(int radix)


InputMismatchExceptionif the next token cannot be translated into a valid int value as described below. If the translation is successful, the scanner advances past the input that matched.


If the next token matches the Integer regular expression defined
above then the token is converted into an int value as if by
removing all locale specific prefixes, group separators, and locale
specific suffixes, then mapping non-ASCII digits into ASCII
digits via

Character.digit

, prepending a
negative sign (-) if the locale specific negative prefixes and suffixes
were present, and passing the resulting string to

Integer.parseInt

with the
specified radix.


radix- the radix used to interpret the token as an int value


InputMismatchException- if the next token does not match the Integer regular expression, or is out of range


NoSuchElementException- if input is exhausted


IllegalStateException- if this scanner is closed


public boolean hasNextLong()


nextLong()method. The scanner does not advance past any input.


IllegalStateException- if this scanner is closed


public boolean hasNextLong(int radix)


nextLong()method. The scanner does not advance past any input.


radix- the radix used to interpret the token as a long value


IllegalStateException- if this scanner is closed


public long nextLong()

An invocation of this method of the form
nextLong() behaves in exactly the same way as the
invocation nextLong(radix), where

radix

is the default radix of this scanner.


InputMismatchException- if the next token does not match the Integer regular expression, or is out of range


NoSuchElementException- if input is exhausted


IllegalStateException- if this scanner is closed


public long nextLong(int radix)


InputMismatchExceptionif the next token cannot be translated into a valid long value as described below. If the translation is successful, the scanner advances past the input that matched.


If the next token matches the Integer regular expression defined
above then the token is converted into a long value as if by
removing all locale specific prefixes, group separators, and locale
specific suffixes, then mapping non-ASCII digits into ASCII
digits via

Character.digit

, prepending a
negative sign (-) if the locale specific negative prefixes and suffixes
were present, and passing the resulting string to

Long.parseLong

with the
specified radix.


radix- the radix used to interpret the token as an int value


InputMismatchException- if the next token does not match the Integer regular expression, or is out of range


NoSuchElementException- if input is exhausted


IllegalStateException- if this scanner is closed


public boolean hasNextFloat()


nextFloat()method. The scanner does not advance past any input.


IllegalStateException- if this scanner is closed


public float nextFloat()


InputMismatchExceptionif the next token cannot be translated into a valid float value as described below. If the translation is successful, the scanner advances past the input that matched.


If the next token matches the Float regular expression defined above
then the token is converted into a float value as if by
removing all locale specific prefixes, group separators, and locale
specific suffixes, then mapping non-ASCII digits into ASCII
digits via

Character.digit

, prepending a
negative sign (-) if the locale specific negative prefixes and suffixes
were present, and passing the resulting string to

Float.parseFloat

. If the token matches
the localized NaN or infinity strings, then either “Nan” or “Infinity”
is passed to

Float.parseFloat

as
appropriate.


InputMismatchException- if the next token does not match the Float regular expression, or is out of range


NoSuchElementException- if input is exhausted


IllegalStateException- if this scanner is closed


public boolean hasNextDouble()


nextDouble()method. The scanner does not advance past any input.


IllegalStateException- if this scanner is closed


public double nextDouble()


InputMismatchExceptionif the next token cannot be translated into a valid double value. If the translation is successful, the scanner advances past the input that matched.


If the next token matches the Float regular expression defined above
then the token is converted into a double value as if by
removing all locale specific prefixes, group separators, and locale
specific suffixes, then mapping non-ASCII digits into ASCII
digits via

Character.digit

, prepending a
negative sign (-) if the locale specific negative prefixes and suffixes
were present, and passing the resulting string to

Double.parseDouble

. If the token matches
the localized NaN or infinity strings, then either “Nan” or “Infinity”
is passed to

Double.parseDouble

as
appropriate.


InputMismatchException- if the next token does not match the Float regular expression, or is out of range


NoSuchElementException- if the input is exhausted


IllegalStateException- if this scanner is closed


public boolean hasNextBigInteger()


BigIntegerin the default radix using the


nextBigInteger()method. The scanner does not advance past any input.


BigInteger


IllegalStateException- if this scanner is closed


public boolean hasNextBigInteger(int radix)


BigIntegerin the specified radix using the


nextBigInteger()method. The scanner does not advance past any input.


radix- the radix used to interpret the token as an integer


BigInteger


IllegalStateException- if this scanner is closed


public BigInteger nextBigInteger()


BigInteger.


An invocation of this method of the form
nextBigInteger() behaves in exactly the same way as the
invocation nextBigInteger(radix), where

radix

is the default radix of this scanner.


InputMismatchException- if the next token does not match the Integer regular expression, or is out of range


NoSuchElementException- if the input is exhausted


IllegalStateException- if this scanner is closed


public BigInteger nextBigInteger(int radix)


BigInteger.


If the next token matches the Integer regular expression defined
above then the token is converted into a BigInteger value as if
by removing all group separators, mapping non-ASCII digits into ASCII
digits via the

Character.digit

, and passing the
resulting string to the

BigInteger(String, int)

constructor with the specified radix.


radix- the radix used to interpret the token


InputMismatchException- if the next token does not match the Integer regular expression, or is out of range


NoSuchElementException- if the input is exhausted


IllegalStateException- if this scanner is closed


public boolean hasNextBigDecimal()


BigDecimalusing the


nextBigDecimal()method. The scanner does not advance past any input.


BigDecimal


IllegalStateException- if this scanner is closed


public BigDecimal nextBigDecimal()


BigDecimal.


If the next token matches the Decimal regular expression defined
above then the token is converted into a BigDecimal value as if
by removing all group separators, mapping non-ASCII digits into ASCII
digits via the

Character.digit

, and passing the
resulting string to the

BigDecimal(String)

constructor.


InputMismatchException- if the next token does not match the Decimal regular expression, or is out of range


NoSuchElementException- if the input is exhausted


IllegalStateException- if this scanner is closed


public Scanner reset()

Resetting a scanner discards all of its explicit state
information which may have been changed by invocations of

useDelimiter(java.util.regex.Pattern)

,

useLocale(java.util.Locale)

, or

useRadix(int)

.

An invocation of this method of the form scanner.reset() behaves in exactly the same way as the invocation


scanner.useDelimiter("\\p{javaWhitespace}+") .useLocale(Locale.getDefault(Locale.Category.FORMAT)) .useRadix(10);


Submit a bug or feature For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.Copyright © 1993, 2024, Oracle and/or its affiliates. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.

Scanner trong Java là gì? Có rất nhiều thảo luận về lớp đặc biệt này trong Java. Cùng CodeGym Hà Nội tìm hiểu, thảo luận về phương thức của nó và hàm tạo lớp trong Java nhé!

Nội dung

Dùng lớp Scanner trong Java

Nhập lớp Scanner xong, chúng ta phải lấy kết quả thể hiện của lớp này để đọc đầu vào từ người dùng.

Ví dụ:

Ta sẽ thực hiện một thí dụ như sau.


import java.util.Scanner; class Main { public static void main(String[] args) { Scanner input = new Scanner(System.in); System.out.print("Nhap mot tu bat ky: "); String chuoi_ky_tu = input.nextLine(); System.out.println(chuoi_ky_tu); input.close(); } }


Kết quả:


Nhap mot tu bat ky: xin chao xin chao


Trong ví dụ trên, câu lệnh:


Scanner input = new Scanner(System.in);


Ở đây, ta đã tạo một đối tượng của lớp Scanner có tên là

input

. Tham số

System.in

được dùng để lấy đầu vào. Tiếp theo, ta đã dùng phương thức

nextLine()

của lớp Scanner để đọc một chuỗi ký tự từ người dùng.

Từ ví dụ trên, ta cần thêm gói

java.util.Scanner

trước khi có thể dùng lớp Scanner.


import java.util.Scanner;


>> Đọc thêm: Khóa học lập trình Java

Cách thức hoạt động của Lớp Scanner

Lớp Scanner đọc toàn bộ dòng ký tự và chia thành các token. Ta có thể tạm hiểu token là các thành phần nhỏ có ý nghĩa đối với trình biên dịch trong Java.

Ví dụ: Giả sử có một chuỗi đầu vào như sau.


Xin chao moi nguoi


Trong trường hợp này, đối tượng lớp Scanner sẽ đọc toàn bộ dòng ký tự và chia thành các token: “Xin”, “chao”, “moi” và “nguoi”. Đối tượng sau đó thực hiện vòng lặp duyệt qua từng token và đọc từng token bằng các phương thức khác nhau.

Chú ý: Theo mặc định, khoảng trắng sẽ được dùng để phân chia các token.

Trên đây là khái niệm và ví dụ cơ bản về lớp Scanner trong Java. Hy vọng các bạn có thể áp dụng được vào trong chương trình của mình. Mọi người hãy tiếp tục theo dõi các bài tiếp theo và cập nhật các bài mới nhất trên CodeGym Hà Nội nhé!

Lớp Scanner trong Java

Lớp Scanner trong Java là một lớp được xác định trước giúp chúng ta lấy đầu vào từ người dùng. Lớp này có trong gói java.util và chúng ta cần nhập gói này vào bên trong chương trình Java của mình để sử dụng lớp này. Có nhiều phương thức được xác định trước trong lớp java.util.Scanner để thực hiện các hoạt động khác nhau như đọc và phân tích cú pháp các kiểu nguyên thủy khác nhau. Về cơ bản, chúng ta phải tạo đối tượng của lớp Scanner để sử dụng các phương thức này. Lớp Scanner cũng có thể phân tích cú pháp chuỗi và kiểu nguyên thủy bằng cách sử dụng biểu thức chính quy.

Lớp Scanner trong Java mở rộng lớp Object và triển khai các giao diện Cloneable và Iterator.

Java

Nhập lớp Scanner trong Java

Để sử dụng các phương thức và chức năng của lớp Scanner, chúng ta cần đưa lớp vào chương trình Java của mình bằng cách nhập gói java.util bằng cách sử dụng từ khóa import ở đầu mã.

Chúng ta có thể làm điều đó theo hai cách sau:

1. import java.util.Scanner;

//nhập lớp Scanner trong Java

1. import java.util.*;

//nhập tất cả các lớp của gói trong java.util

What does import java.util Scanner mean?

The

java.util.Scanner

class is one of the first components that new Java developers encounter. To use it in your code, you should import it, although another option is to explicitly reference the package in your code.

There are multiple ways to import the Java Scanner class into your code.

Java’s Scanner class makes it easy to get input from the user, which allows simple programs to quickly become interactive. And a little bit of interactivity always makes learning how to program a computer just a little bit more fun.

However, there is one minor complexity the Java Scanner class add into the software development mix.

In order to use the Java Scanner class in your code, you must either fully reference the java.util package when you call the Scanner, or you must add a Java Scanner import statement at the start of your class.

To keep your code readable and less verbose, a Java Scanner import is recommended.

When you add an import statement to your code, you are telling the Java compiler that you need access to a class that isn’t accessible by default. The

java.util.Scanner

import statement at the top of many Java classes means that somewhere in the code, the Scanner class is being used.

Java user input made easy

Learn the easiest ways to handle user input in Java, and format any console output with printf.

Java User Input

The

Scanner

class is used to get
user input, and it is found in the

java.util

package.

To use the

Scanner

class, create an object of the class and use any of the available methods found in the

Scanner

class documentation.
In our example, we will use the

nextLine()

method, which is used to read Strings:

Example


import java.util.Scanner; // Import the Scanner class class Main { public static void main(String[] args) { Scanner myObj = new Scanner(System.in); // Create a Scanner object System.out.println("Enter username"); String userName = myObj.nextLine(); // Read user input System.out.println("Username is: " + userName); // Output user input } }


If you don’t know what a package is, read our Java Packages Tutorial.

Conclusion

The Scanner in Java is a vital tool for speeding up user input processing in Java. It enables developers to create interactive apps capable of smoothly integrating user interactions because of its vast number of techniques specialized to different data kinds. Discovering the Scanner class in Java’s complexities will set you on a path to developing Java apps that are more engaging and user-focused. You will improve user experiences and optimize data aggregation within your Java endeavors as you apply your newly acquired skill in real settings, eventually influencing the development of a more complex programming environment.

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If you have any questions or doubts, feel free to post them in the comments section below. Our team will get back to you at the earliest.

Create a Scanner Object in Java

Once we import the package, here is how we can create

Scanner

objects.


// read input from the input stream Scanner sc1 = new Scanner(InputStream input); // read input from files Scanner sc2 = new Scanner(File file); // read input from a string Scanner sc3 = new Scanner(String str);


Here, we have created objects of the

Scanner

class that will read input from InputStream, File, and String respectively.

Hàm tạo của lớp Scanner trong Java

Lớp Scanner chứa các hàm tạo cho các mục đích cụ thể mà chúng ta có thể sử dụng trong chương trình Java của mình.

STT	Hàm tạo	Mô tả
Scanner (Nguồn tệp)	tạo đối tượng Scanner tạo ra các giá trị được quét từ tệp được chỉ định
Scanner (File source, String charsetName)	xây dựng đối tượng Scanner tạo ra các giá trị được quét từ tệp được chỉ định
Scanner (InputStream source)	tạo một đối tượng Scanner mới tạo ra các giá trị được quét từ luồng đầu vào được chỉ định.
Scanner (InputStream source, String charsetName)	tạo một Scanner mới tạo ra các giá trị được quét từ luồng đầu vào được chỉ định.
Scanner (Readable source)	tạo một Scanner mới tạo ra các giá trị được quét từ nguồn được chỉ định.
Scanner (String source)	tạo một Scanner mới tạo ra các giá trị được quét từ chuỗi được chỉ định.
Scanner (ReadableByteChannel source)	tạo một Scanner mới tạo ra các giá trị được quét từ kênh được chỉ định.
Scanner (ReadableByteChannel source, String charsetName)	tạo một Máy quét mới tạo ra các giá trị được quét từ kênh được chỉ định.
Scanner (Path source)	tạo một Scanner mới tạo ra các giá trị được quét từ tệp được chỉ định.
10	Scanner (Path source, String charsetName)	tạo một Scanner mới tạo ra các giá trị được quét từ tệp được chỉ định

>>> Đọc thêm: Lập trình Socket trong Java – Nâng cấp kỹ năng lập trình Java của bạn

What does import java.util Scanner mean?

The

java.util.Scanner

class is one of the first components that new Java developers encounter. To use it in your code, you should import it, although another option is to explicitly reference the package in your code.

There are multiple ways to import the Java Scanner class into your code.

Java’s Scanner class makes it easy to get input from the user, which allows simple programs to quickly become interactive. And a little bit of interactivity always makes learning how to program a computer just a little bit more fun.

However, there is one minor complexity the Java Scanner class add into the software development mix.

In order to use the Java Scanner class in your code, you must either fully reference the java.util package when you call the Scanner, or you must add a Java Scanner import statement at the start of your class.

To keep your code readable and less verbose, a Java Scanner import is recommended.

When you add an import statement to your code, you are telling the Java compiler that you need access to a class that isn’t accessible by default. The

java.util.Scanner

import statement at the top of many Java classes means that somewhere in the code, the Scanner class is being used.

Java user input made easy

Learn the easiest ways to handle user input in Java, and format any console output with printf.

Kết luận

Lớp Scanner trong Java bạn có thể hiểu và tưởng tượng là một “cái máy in”, có thể nhập và xuất ra dữ liệu. Bài viết trên đã giới thiệu cho bạn về lớp Scanner trong Java, cho bạn rõ hơn định nghĩa Scanner trong Java là gì? Và các phương thức và hàm tạo của lớp Scanner. Mong rằng bạn có thể hiểu rõ hơn về Scanner trong Java qua bài viết này. Tìm hiểu thêm về Java và các ngôn ngữ lập trình khác qua các khóa học lập trình chuyển nghiệp tại CodeGym Hà Nội bạn nhé!

Tin bài liên quan:

https://hanoi.codegym.vn/blog/co-nen-hoc-java-web-khong/

https://hanoi.codegym.vn/blog/lo-trinh-hoc-lap-trinh-java-hieu-qua/

Java Scanner

Scanner class in Java is found in the java.util package. Java provides various ways to read input from the keyboard, the java.util.Scanner class is one of them.

The Java Scanner class breaks the input into tokens using a delimiter which is whitespace by default. It provides many methods to read and parse various primitive values.

The Java Scanner class is widely used to parse text for strings and primitive types using a regular expression. It is the simplest way to get input in Java. By the help of Scanner in Java, we can get input from the user in primitive types such as int, long, double, byte, float, short, etc.

The Java Scanner class extends Object class and implements Iterator and Closeable interfaces.

The Java Scanner class provides nextXXX() methods to return the type of value such as nextInt(), nextByte(), nextShort(), next(), nextLine(), nextDouble(), nextFloat(), nextBoolean(), etc. To get a single character from the scanner, you can call next().charAt(0) method which returns a single character.

Example 2: Java Scanner nextInt()


import java.util.Scanner; class Main { public static void main(String[] args) { // creates a Scanner object Scanner input = new Scanner(System.in); System.out.println("Enter an integer: "); // reads an int value int data1 = input.nextInt(); System.out.println("Using nextInt(): " + data1); input.close(); } }


Output

Enter an integer: 22 Using nextInt(): 22

In the above example, we have used the

nextInt()

method to read an integer value.

Java Scanner Methods

The Java Scanner class also comes with several methods to create more robust input collection techniques. In addition, scanner methods can help develop stringent rules and guidelines for user input, like the type and the amount of data it can accept.

Combining the Scanner with other functions, methods, etc., makes it an even more powerful tool. For example, you can ensure that only permitted characters get validated and entered into the software database. In video game development, you can use it to build a character creation phase, where a user will enter information like their name.

• nextInt(): Reads a single int value from the input. (Format: Unbroken number)
• nextFloat(): Reads a single float value from the input. (Format: Up to 32 digit decimal)
• nextBloolean(): Reads a single boolean value from the input. (true/false)
• nextLine(): Reads a single line value from the input. (stops at \n)
• next(): Reads a single word value from the input. (stops at “whitespace”)
• nextByte(): Reads a single byte value from the input.
• nextDouble(): Reads a single int value from the input. (Format: Up to 64 digit decimal)
• nextShort(): Reads a single short value from the input. (-32,768 to 32,767)
• nextLong(): Reads a single long value from the input. (-9,223,372,036,854,775,807 to 9,223,372,036,854,775,808)

Example 3

Output:

The

Scanner

class of the

java.util

package is used to read input data from different sources like input streams, files, etc. Let’s take an example.

What is a wildcard import in Java?

There are over 100 classes in the java.util package.

When you import the Java scanner with the import

java.util.*;

statement, you gain access to each class in the java.util package without adding any more import statements.

In contrast, when an explicit Java Scanner import is performed with the import

java.util.Scanner;

statement, only the Scanner class becomes available to your code. To use other classes in the java.util package, you must add explicit imports of those classes.

For the sake of simplicity, I recommend new developers use the wildcard approach wto import the Java Scanner class. It requires fewer keystrokes and reduces the opportunity to introduce compile-timer errors into your code.

package com.mcnz.example; // This example uses the wildcard import syntax import java.util.*; public class ScannerUserInput { public static void main(String[] args) { // String input with the Java Scanner System.out.println(“How old are you?”); Scanner stringScanner = new Scanner(System.in); String age = stringScanner.next(); System.out.println(age + ” is a good age to be!”); } }

Furthermore, if you use an IDE such as Eclipse or VS Code, an import formatter will convert wildcards imports to explicit imports when you finish development.

Senior developers find that implicit imports lead to more readable code, and also avoid possible import collisions when a class appears in two separate packages. For example, the Date class exists in both the java.util and java.sql packages, which can lead to a great deal of confusion if an application uses both packages.

Does a wildcard import hurt performance?

Some developer think doing a

java.util.*;

import might impact the performance of their code because so many classes become available to your program. However, this is not true. The wildcard import simply makes every class in a package available while you develop your app. It has no impact on the size of the application that eventually gets built.

Java Scanner Class Methods

The following are the list of Scanner methods:

SN	Modifier & Type	Method	Description
1)	void	close()	It is used to close this scanner.
2)	pattern	delimiter()	It is used to get the Pattern which the Scanner class is currently using to match delimiters.
3)	Stream	findAll()	It is used to find a stream of match results that match the provided pattern string.
4)	String	findInLine()	It is used to find the next occurrence of a pattern constructed from the specified string, ignoring delimiters.
5)	string	findWithinHorizon()	It is used to find the next occurrence of a pattern constructed from the specified string, ignoring delimiters.
6)	boolean	hasNext()	It returns true if this scanner has another token in its input.
7)	boolean	hasNextBigDecimal()	It is used to check if the next token in this scanner’s input can be interpreted as a BigDecimal using the nextBigDecimal() method or not.
8)	boolean	hasNextBigInteger()	It is used to check if the next token in this scanner’s input can be interpreted as a BigDecimal using the nextBigDecimal() method or not.
9)	boolean	hasNextBoolean()	It is used to check if the next token in this scanner’s input can be interpreted as a Boolean using the nextBoolean() method or not.
10)	boolean	hasNextByte()	It is used to check if the next token in this scanner’s input can be interpreted as a Byte using the nextBigDecimal() method or not.
11)	boolean	hasNextDouble()	It is used to check if the next token in this scanner’s input can be interpreted as a BigDecimal using the nextByte() method or not.
12)	boolean	hasNextFloat()	It is used to check if the next token in this scanner’s input can be interpreted as a Float using the nextFloat() method or not.
13)	boolean	hasNextInt()	It is used to check if the next token in this scanner’s input can be interpreted as an int using the nextInt() method or not.
14)	boolean	hasNextLine()	It is used to check if there is another line in the input of this scanner or not.
15)	boolean	hasNextLong()	It is used to check if the next token in this scanner’s input can be interpreted as a Long using the nextLong() method or not.
16)	boolean	hasNextShort()	It is used to check if the next token in this scanner’s input can be interpreted as a Short using the nextShort() method or not.
17)	IOException	ioException()	It is used to get the IOException last thrown by this Scanner’s readable.
18)	Locale	locale()	It is used to get a Locale of the Scanner class.
19)	MatchResult	match()	It is used to get the match result of the last scanning operation performed by this scanner.
20)	String	next()	It is used to get the next complete token from the scanner which is in use.
21)	BigDecimal	nextBigDecimal()	It scans the next token of the input as a BigDecimal.
22)	BigInteger	nextBigInteger()	It scans the next token of the input as a BigInteger.
23)	boolean	nextBoolean()	It scans the next token of the input into a boolean value and returns that value.
24)	byte	nextByte()	It scans the next token of the input as a byte.
25)	double	nextDouble()	It scans the next token of the input as a double.
26)	float	nextFloat()	It scans the next token of the input as a float.
27)	int	nextInt()	It scans the next token of the input as an Int.
28)	String	nextLine()	It is used to get the input string that was skipped of the Scanner object.
29)	long	nextLong()	It scans the next token of the input as a long.
30)	short	nextShort()	It scans the next token of the input as a short.
31)	int	radix()	It is used to get the default radix of the Scanner use.
32)	void	remove()	It is used when remove operation is not supported by this implementation of Iterator.
33)	Scanner	reset()	It is used to reset the Scanner which is in use.
34)	Scanner	skip()	It skips input that matches the specified pattern, ignoring delimiters
35)	Stream	tokens()	It is used to get a stream of delimiter-separated tokens from the Scanner object which is in use.
36)	String	toString()	It is used to get the string representation of Scanner using.
37)	Scanner	useDelimiter()	It is used to set the delimiting pattern of the Scanner which is in use to the specified pattern.
38)	Scanner	useLocale()	It is used to sets this scanner’s locale object to the specified locale.
39)	Scanner	useRadix()	It is used to set the default radix of the Scanner which is in use to the specified radix.

What is a wildcard import in Java?

There are over 100 classes in the java.util package.

When you import the Java scanner with the import

java.util.*;

statement, you gain access to each class in the java.util package without adding any more import statements.

In contrast, when an explicit Java Scanner import is performed with the import

java.util.Scanner;

statement, only the Scanner class becomes available to your code. To use other classes in the java.util package, you must add explicit imports of those classes.

For the sake of simplicity, I recommend new developers use the wildcard approach wto import the Java Scanner class. It requires fewer keystrokes and reduces the opportunity to introduce compile-timer errors into your code.

package com.mcnz.example; // This example uses the wildcard import syntax import java.util.*; public class ScannerUserInput { public static void main(String[] args) { // String input with the Java Scanner System.out.println(“How old are you?”); Scanner stringScanner = new Scanner(System.in); String age = stringScanner.next(); System.out.println(age + ” is a good age to be!”); } }

Furthermore, if you use an IDE such as Eclipse or VS Code, an import formatter will convert wildcards imports to explicit imports when you finish development.

Senior developers find that implicit imports lead to more readable code, and also avoid possible import collisions when a class appears in two separate packages. For example, the Date class exists in both the java.util and java.sql packages, which can lead to a great deal of confusion if an application uses both packages.

Does a wildcard import hurt performance?

Some developer think doing a

java.util.*;

import might impact the performance of their code because so many classes become available to your program. However, this is not true. The wildcard import simply makes every class in a package available while you develop your app. It has no impact on the size of the application that eventually gets built.

Scanner trong java là gì?

Có nhiều bạn hỏi “Scanner java là gì?” hay “Scanner trong java là gì?”

Scanner trong Java là gì?

Scanner trong Java là lớp được dùng để đọc dữ liệu đầu vào từ các nguồn khác nhau như luồng đầu vào, người dùng, tệp. Đây là lớp có trong gói java.util, và gói này cần được nhập vào bên trong chương trình java để lớp scanner được chạy. Với nhiều phương thức được xác định trước trong lớp java.util.Scanner để thực hành các hoạt động khác nhau như: đọc hay phân tách cú pháp những kiểu nguyên thủy khác nhau. Bằng cách dùng biểu thức chính quy, lớp Scanner cũng có thể phân tích cú pháp dạng chuỗi và kiểu nguyên thủy

Lớp Scanner trong Java mở rộng lớp Object và triển khai được các giao diện Cloneable và Iterator.

Why must we import the Java Scanner class?

With no added import statements to your code, your Java app has default access to all of the classes in the java.lang package. This includes classes such as:

• String
• System
• Integer
• Double
• Math
• Exception
• Thread

However, to use any classes in packages other than java.lang in your code, an import is required.

The Scanner class is found in the java.util package, not java.lang.

Since the Scanner class is found outside of java.lang, you must either directly reference the java.util package every time you use the Scanner, or just add a single Scanner import statement to your Java file.

Input Types

In the example above, we used the

nextLine()

method, which is used to read Strings. To read other types, look at the table below:

Method	Description
Reads a
Reads a
Reads a
Reads a
Reads a
Reads a
Reads a
Reads a

In the example below, we use different methods to read data of various types:

Example


import java.util.Scanner; class Main { public static void main(String[] args) { Scanner myObj = new Scanner(System.in); System.out.println("Enter name, age and salary:"); // String input String name = myObj.nextLine(); // Numerical input int age = myObj.nextInt(); double salary = myObj.nextDouble(); // Output input by user System.out.println("Name: " + name); System.out.println("Age: " + age); System.out.println("Salary: " + salary); } }


Note: If you enter wrong input (e.g. text in a numerical input), you will get an exception/error message (like “InputMismatchException”).

You can read more about exceptions and how to handle errors in the Exceptions chapter.

In software development, the program will inevitably require information for the user at some point. For example, some websites may only require an age to view the content, while video games require a constant flow of user input. However, capturing user input and putting it to use is a subject that tends to be under-discussed, so let’s talk about it.

In this post, you will discover the Java class called Scanner and how to create an instance of it. You will also learn about the different methods that come with it and how they extend or specify the behavior of the scanner class. Finally, you will see some code examples from the view of developing a simple character creation phase for a hypothetical video game.

• How to Import Scanner in Java
• Java Scanner Methods
• How to Use Scanner in Java
• How to Start Scanning for User Input With Java

Without further delay, let’s jump right in.

Các phương thức của lớp Scanner để lấy đầu vào

Lớp Scanner cung cấp các phương thức khác nhau cho phép chúng ta đọc các đầu vào thuộc các kiểu khác nhau.

Phương thức	Mô tả
nextInt()	Đọc một giá trị kiểu int.
nextFloat()	Đọc một giá trị kiểu float.
nextBoolean()	Đọc một giá trị kiểu Boolean.
nextLine()	Đọc một dòng văn bản.
next()	Đọc một từ.
nextByte()	Đọc một giá trị ở dạng byte.
nextDouble()	Đọc một giá trị kiểu double.
nextShort()	Đọc một giá trị kiểu short.
nextLong()	Đọc một giá trị kiểu long.

Có thể hiểu phương thức của Scanner bằng một ví dụ thực tiễn sau:


import java.util.Scanner; class Main { public static void main(String[] args) { Scanner input = new Scanner(System.in); System.out.println("Nhap mot so nguyen: "); int a = input.nextInt(); System.out.println(a); input.close(); } }


Kết quả:


Nhap mot so nguyen: 4 4 hasNextXYZ ()


Trong ví dụ trên, chúng ta đã dùng phương thức nextInt() để đọc 1 giá trị là số nguyên.

Nextline trong java là gì?Hasnextline trong java là gì

Đôi lúc ta cần kiểm tra xem giá trị tiếp theo ta đọc có thuộc một loại nào không, hoặc đầu vào có EOF hay không. Tiếp theo, mình nên kiểm tra xem đầu vào của máy quét có thuộc loại mình muốn hay không? Với sự trợ giúp của các hàm hasNextXYZ () trong đó XYZ là kiểu dữ liệu mà minh muốn dùng. Phương thức trả về true (đúng) khi máy quét có mã thông báo thuộc loại đó ngược lại trả về false (sai). Với một số phương thức boolean cho mỗi mẫu dữ liệu. Để ta rà soát xem mã thông báo tiếp theo của một mẫu dữ liệu cụ thể có sẵn trong đầu vào nhất định hay không?

Ta có bảng sau:

Phương thức	Mô tả
boolean hasNextBoolean ()	kiểm tra mã thông báo tiếp theo trong đầu vào của máy quét này có hiểu Boolean bằng phương thức nextBoolean () hay không
boolean hasNextByte ()	kiểm tra xem mã thông báo tiếp theo trong đầu vào của máy quét này có hiểu là Byte bằng cách dùng phương thức nextByte () hay không
boolean hasNextDouble ()	kiểm tra mã thông báo tiếp theo trong máy quét này có phải đầu vào BigDecimal bằng cách dùng phương thức nextBigDecimal () hay không
boolean hasNextFloat ()	Phương pháp này kiểm tra xem mã thông báo tiếp theo trong đầu vào của máy quét này có hiểu một Float bằng cách dùng phương thức nextFloat () hay không
boolean hasNextInt ()	kiểm tra mã thông báo tiếp theo trong đầu vào của máy quét này có hiểu một int dùng phương thức nextInt () hay không
boolean hasNextLine ()	kiểm tra có dòng khác trong đầu vào của máy quét này hay không
boolean hasNextLong ()	kiểm tra mã thông báo tiếp theo trong đầu vào của máy quét này có hiểu Long bằng phương thức nextLong () hay không.

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