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Java Try Catch Else | Thứ Tự Ưu Tiên Của Catch

Try Catch Java Tutorial #46

Java


class


GFG


public


static


void


main (String[] args)


int


[] arr =


new


int


];


try


int


i = arr[


];


System.out.println(


"Inside try block"


);


catch


(ArrayIndexOutOfBoundsException ex)


System.out.println(


"Exception caught in Catch block"


);


System.out.println(


"Outside try-catch clause"


);

Output

Exception caught in Catch block
Outside try-catch clause

  • Control flow in try-catch-finally clause :

Sử dụng try-catch-finally trong thực tế

Khối lệnh trong finally sẽ luôn được thực hiện vì thế sử dụng finally để đảm bảo một thứ gì đó luôn được thực hiện cho dù có xảy ra exception hay khômg.

Ví dụ khi bạn sử dụng java.io để đọc và ghi file. Việc đầu tiên chúng ta cần làm đó là mở file, sau khi mọi thao tác đã hoàn tất thì chúng ta cần phải đóng kết nối để trả tài nguyên lại cho các nguồn khác sử dụng. Việc đóng kết nối phải được thực thi cuối cùng và nếu chẳng may ở bên trên xảy ra exception thì lệnh đóng kết nối sẽ không được thực hiện.

import java.io.FileReader; class Example { public static void main(String args[]) { try { FileReader fileReader = new FileReader(“D:\\test.txt”); // do something fileReader.close(); } catch (Exception ex) { ex.printStackTrace(); } } }

Chúng ta cần kết hợp thêm finally để đảm bảo rằng kết nối sẽ luôn được đóng kể cả khi xảy ra exception.

import java.io.FileReader; import java.io.IOException; class Example { public static void main(String args[]) { FileReader fileReader = null; try { fileReader = new FileReader(“D:\\test.txt”); // do something } catch (Exception ex) { ex.printStackTrace(); } finally { try { if(fileReader != null) { fileReader.close(); } } catch (IOException e) { e.printStackTrace(); } } } }

Để ý rằng bên trong finally có kết hợp try-catch để xử lý lỗi trong trường close có thể ném ra IOException. Tuy nhiên đối với trường hợp exception xảy ra trong finally chúng ta chỉ cần ghi log lại là xong. Ví dụ như việc đóng file trên, cuối cùng đã cố tình đóng rồi mà còn không cho thì biết làm sao đây? log lại và bảo trì hệ thống thôi =).

Try Catch Java Tutorial #46
Try Catch Java Tutorial #46

Conclusion

In this tutorial, we have covered the basics of Java exception handling using try, catch, and finally blocks. Understanding these concepts is crucial for developing robust Java applications that can handle unexpected errors gracefully. If you’re looking to hire remote Java developers or enhance your skills in Java development, mastering exception handling is a must.

How Are Try-Catch and Try-Except Blocks Similar?

Both follow a similar syntactic pattern. You encase potentially error-prone code within a

try

block and then the

catch

and

except

blocks define actions to handle those errors.

The syntax of the

try-except

block in Python is as follows:


try: # some code here that might raise an exception except ExceptionType: # handle the exception here

In Java, the syntax for the

try-catch

block is as follows:


try { // some code here that might throw an exception } catch (ExceptionType e) { // handle the exception here }

Exception Handling in Java Tutorial
Exception Handling in Java Tutorial

Java


class


GFG


public


static


void


main (String[] args)


int


[] arr =


new


int


];


try


int


i = arr[


];


System.out.println(


"Inside try block"


);


catch


(NullPointerException ex)


System.out.println(


"Exception has been caught"


);


System.out.println(


"Outside try-catch clause"


);

Run Time Error:

Exception in thread “main” java.lang.ArrayIndexOutOfBoundsException: 4
at GFG.main(GFG.java:12)

  • try-catch-finally clause :

Finally

The

finally

statement lets you execute code, after

try...catch

, regardless of the result:

Example


public class Main { public static void main(String[] args) { try { int[] myNumbers = {1, 2, 3}; System.out.println(myNumbers[10]); } catch (Exception e) { System.out.println("Something went wrong."); } finally { System.out.println("The 'try catch' is finished."); } } }

The output will be:


Something went wrong.The 'try catch' is finished.

#77 Exception Handling Using try catch in Java
#77 Exception Handling Using try catch in Java

Java


class


GFG


public


static


void


main (String[] args)


try


String str =


"123"


int


num = Integer.parseInt(str);


System.out.println(


"try block fully executed"


);


catch


(NumberFormatException ex)


System.out.println(


"catch block executed..."


);


finally


System.out.println(


"finally block executed"


);


System.out.println(


"Outside try-catch-finally clause"


);

Output

try block fully executed
finally block executed
Outside try-catch-finally clause

Control flow in try-finally

In this case, no matter whether an exception occurs in try-block or not finally will always be executed. But control flow will depend on whether an exception has occurred in the try block or not.

1. Exception raised: If an exception has occurred in the try block then the control flow will be finally block followed by the default exception handling mechanism.

Catching Exceptions

If a method calls another method that throws checked exceptions, the calling method is forced to either pass the exception on, or catch it. Catching the exception is done using a try-catch block. Here is an example:

public void callDivide(){ try { int result = divide(2,1); System.out.println(result); } catch (BadNumberException e) { //do something clever with the exception System.out.println(e.getMessage()); } System.out.println(“Division attempt done”); }

The BadNumberException parameter e inside the catch-clause points to the exception thrown from the divide method, if an exception is thrown.

If no exeception is thrown by any of the methods called or statements executed inside the try-block, the catch-block is simply ignored. It will not be executed.

If an exception is thrown inside the try-block, for instance from the divide method, the program flow of the calling method, callDivide, is interrupted just like the program flow inside divide. The program flow resumes at a catch-block in the call stack that can catch the thrown exception. In the example above the “System.out.println(result);” statement will not get executed if an exception is thrown fromt the divide method. Instead program execution will resume inside the “catch (BadNumberException e) { }” block.

If an exception is thrown inside the catch-block and that exception is not caught, the catch-block is interrupted just like the try-block would have been.

When the catch block is finished the program continues with any statements following the catch block. In the example above the “System.out.println(“Division attempt done”);” statement will always get executed.

Java for Testers #33 - Try Catch Java | Exception Handling in Java
Java for Testers #33 – Try Catch Java | Exception Handling in Java

Tóm lược

try-catch-finally là cơ chế để xử lý exception trong java mà chúng ta cần nắm rõ để xử lý tốt các exception. Finally luôn là công cụ mạnh mẽ để đảm bảo cho một thứ gì đó luôn được thực thi. Thế nhưng các khối lệnh trong finally thường lặp đi lặp lại giống nhau khiến cho code bị trùng lặp khá nhiều. Ví như đoạn đóng kết nối trên là cứ khi làm việc với class nào bên trong package java.io chúng ta đều phải thêm vào, để giải quyết vấn đề này chúng ta có thêm cơ chế mới try-with-resource mà chúng ta sẽ tìm hiểu ở phần sau.

Try catch vs If else

Các bác có thể cho biết sự khác nhau chính giữa try catch và if else k ạ, e có gg rồi mà cần xin thêm ý kiến của các bác, tks all !

4 CÂU TRẢ LỜI

  • try catch là để bắt lỗi ngoại lệ : khi trong try lỗi thì sẽ thực thi các thao tác trong catch,
  • if else là câu lệnh rẽ nhánh: kiếm tra điều kiện ở if mà đúng thì thực hiện lệnh trong if, sai thì thực hiện lệnh trong else

tks bác

Trong câu lệnh try/catch, phần try luôn được thực thi và bất kỳ ngoại lệ (thường là lỗi) nào trong khi thực thi ở bất kỳ đâu trong phần try sẽ chuyển sang phần catch, nếu ko catch được thì nó sẽ bỏ qua. Trong câu lệnh if/else, phần if hoặc phần else được thực thi sau khi kiểm tra điều kiện để chạy vào

Theo mình thấy thì nó sẽ như thế này. Bạn muốn thực hiện điều gì đó và nếu nó có lỗi trong quá trình thực hiện thì sẽ thông báo lỗi hoặc làm 1 hành động do bạn quy định thì sẽ sử dụng try – catch. Còn bạn muốn phân chia hành động ra theo các trường hợp khác nhau thì dùng if – else

  • If else là khối lệnh để bạn kiểm tra một điều kiện cho trước bằng các toán tử: ==, <, >,..etc.. Cái này chắc bạn biết rồi

  • Còn try catch là khối lệnh dùng để kiểm thử một đoạn code có bị xảy ra Exception hay không, Exception có thể coi là một lỗi khi chạy đoạn code, ví dụ:


try { $name = 'Toi la con vit con'; echo $name; } catch ($error) { echo 'Code loi roi anh ey'; }

Đoạn code này đang kiểm tra các câu lệnh trong khối try, nhưng vì các câu lệnh này không hề có lỗi, nên câu echo trong đoạn catch sẽ không được chạy

Giờ hãy nhìn vào đoạn code này:


try { echo $name; $name = 'Toi la con vit con'; } catch ($error) { echo 'Code loi roi anh ey'; }

Lúc này trên màn hình sẽ in ra “Code loi roi anh ey” Vì trong đoạn try đã có lỗi xảy ra, biến $name được sử dụng khi chưa được khai báo.

Các lỗi về cú pháp, ví dụ như thiếu dấu chấm phẩy, thiếu dấu mở ngoặc, … sẽ không được tính là Exception

vậy trong ex cuối của bác đoạn đó là lỗi syntax thôi phải k bác

@duongricky không bạn, lỗi đó không phải lỗi syntax, syntax là lỗi kiểu bạn gõ thiếu cú pháp ấy, còn lỗi kia là lỗi logic của phép toán, khi $name chưa được khai báo nhưng đã được sử dụng

@hongquanfit ok bác

Em muốn hỏi về hiệu năng của try/catch và if else ạ? Nếu trong trường hợp có thể dùng cả 2 hoặc try/catch hoặc if-else thì nên ưu tiên try/catch hay if-else ạ?

@huannguyen try catch và if else là 2 khối lệnh khác nhau để thực hiện 2 công việc khác nhau, nên không thể so sánh hay ưu tiên cái nào đâu bạn nhé

@hongquanfit em đồng ý, cảm ơn bác, so sánh khập khiểng quá, mới đăng ký acc trên này vào cmt đầu fail quá 😢

Basic try-catch-finally Exception Handling in Java

Jakob Jenkov

This text summarizes the basics of how try-catch-finally clause error handling works. The examples are in Java, but the rules are the same for C#. The only difference between Java and C# exceptions is that C# doesn’t have checked exceptions. Checked and unchecked exceptions are explained in more detail in a different text.

Exceptions are used in a program to signal that some error or exceptional situation has occurred, and that it doesn’t make sense to continue the program flow until the exception has been handled. A method may throw an exception for many reasons, for instance if the input parameters are invalid (negative when expecting positive etc.).

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In this tutorial, we will cover the fundamentals of Java exception handling, including the try, catch, and finally blocks. Exception handling is an essential technique for software developers to ensure that their applications are robust and can handle unexpected errors gracefully. By the end of this tutorial, you will have a solid understanding of how to handle exceptions in Java effectively.

Java exception handling ⚠️
Java exception handling ⚠️

Try Block

The

try

block is used to enclose a section of code that might throw an exception. When an exception is thrown within the try block, the code inside the block stops executing, and the control is transferred to the appropriate

catch

block. If no exception occurs, the catch block is skipped.

Here’s an example of a try block:


try { int result = 10 / 0; System.out.println("The result is: " + result); } catch (ArithmeticException e) { System.out.println("An error occurred: " + e.getMessage()); }

Thứ tự ưu tiên của catch

Chúng ta có thể catch nhiều exception bên dưới khối lệnh được bao bọc bởi try. Khi có một exception xảy ra chương trình sẽ duyệt tuần tự các khối catch theo thứ tự được khai báo cho đến khi tìm thấy catch với exception tương ứng thì sẽ tiến hành thực thi khối lệnh bên trong nó và bỏ qua các khối catch bên dưới.

import java.io.*; // A Class that uses above MyException public class Main { // Driver Program public static void main(String args[]) { try { throw new FileNotFoundException(); } catch (ArrayIndexOutOfBoundsException e) { System.out.println(“ArrayIndexOutOfBoundsException”); } catch (FileNotFoundException e) { System.out.println(“FileNotFoundException”); } } }

Output: FileNotFoundException

Note: Nếu chúng ta khai báo một subexception của một exception ở phía sau nó thì exception sẽ bị lỗi tại thời điểm biên dịch vì các subexception này sẽ không bao giờ được gọi bởi exception cha đã bao quát nó.

import java.io.*; // A Class that uses above MyException public class Main { // Driver Program public static void main(String args[]) { try { throw new FileNotFoundException(); } catch (Exception e) { System.out.println(“ArrayIndexOutOfBoundsException”); } catch (FileNotFoundException e) { System.out.println(“FileNotFoundException”); } } }

Output: Error:(11, 11) java: exception java.io.FileNotFoundException has already been caught

Java Tutorial - TRY CATCH for handling exceptions
Java Tutorial – TRY CATCH for handling exceptions

Catch Block

The

catch

block is used to handle the exception thrown by the try block. It is placed immediately after the try block and takes an exception object as a parameter. You can have multiple catch blocks to handle different types of exceptions. When an exception is thrown, the appropriate catch block is executed, and the program continues with the next statement after the catch block.

Here’s an example of using multiple catch blocks:


try { int[] numbers = new int[3]; numbers[5] = 10; } catch (ArrayIndexOutOfBoundsException e) { System.out.println("Array index out of bounds: " + e.getMessage()); } catch (NullPointerException e) { System.out.println("Null pointer: " + e.getMessage()); }

Java try and catch

The

try

statement allows you to define a block of code to be
tested for errors while it is being executed.

The

catch

statement allows you to define a block of code to
be executed, if an error occurs in the try block.

The

try

and

catch

keywords
come in pairs:

Syntax


try { // Block of code to try } catch(Exception e) { // Block of code to handle errors }

Consider the following example:

This will generate an error, because myNumbers[10] does not exist.


public class Main { public static void main(String[ ] args) { int[] myNumbers = {1, 2, 3}; System.out.println(myNumbers[10]); // error! } }

The output will be something like this:


Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 10at Main.main(Main.java:4)

If an error occurs, we can use

try...catch

to catch the error and execute some code to handle it:

Example


public class Main { public static void main(String[ ] args) { try { int[] myNumbers = {1, 2, 3}; System.out.println(myNumbers[10]); } catch (Exception e) { System.out.println("Something went wrong."); } } }

The output will be:


Something went wrong.

Try / Catch & Exceptions | Java | Tutorial 25
Try / Catch & Exceptions | Java | Tutorial 25

Finally Block

The

finally

block is used to execute code that must run regardless of whether an exception was thrown or not. It is placed after the try and catch blocks and is executed after the try and catch blocks have completed their execution. The finally block can be used to release resources, such as file handles or network connections, that must be closed regardless of whether an exception has occurred or not.

Here’s an example of using a finally block:


try { int result = 10 / 0; System.out.println("The result is: " + result); } catch (ArithmeticException e) { System.out.println("An error occurred: " + e.getMessage()); } finally { System.out.println("This will always be executed."); }

Catch or Propagate Exceptions?

You might be wondering whether you should catch or propate exceptions thrown in your program. It depends on the situation. In many applications you can’t really do much about the exception but tell the user that the requested action failed. In these applications you can usually catch all or most exceptions centrally in one of the first methods in the call stack. You may still have to deal with the exception while propagating it though (using finally clauses). For instance, if an error occurs in the database connection in a web application, you may still have to close the database connection in a finally clause, even if you can’t do anything else than tell the user that the action failed. How you end up handling exceptions also depends on whether you choose checked or unchecked exceptions for your application. There is more on that in other texts in the error handling trail.

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Jakob Jenkov

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High-Performance

Java Persistence

Are you confused when to use

try-except

versus

try-catch

? Both are popular mechanisms that gracefully handle unexpected situations. Both share a similar philosophy in syntax, where a block of code is ‘tried,’ and if an exception occurs, it’s caught and handled in a designated way. There’s one big difference between them though:

try-except

is for Python while

try-catch

is for Java.

No matter what language you’re more experienced in, here are the parallels and discrepancies you need to know to master both.

Top 10 Cổ Phiếu Phục Hồi Mạnh - Sinh Lãi Gấp 3 Lần Vnindex
Top 10 Cổ Phiếu Phục Hồi Mạnh – Sinh Lãi Gấp 3 Lần Vnindex

Example: Catching IOException’s

If an exception is thrown during a sequence of statements inside a try-catch block, the sequence of statements is interrupted and the flow of control will skip directly to the catch-block. This code can be interrupted by exceptions in several places:

public void openFile(){ try { // constructor may throw FileNotFoundException FileReader reader = new FileReader(“someFile”); int i=0; while(i != -1){ //reader.read() may throw IOException i = reader.read(); System.out.println((char) i ); } reader.close(); System.out.println(“— File End —“); } catch (FileNotFoundException e) { //do something clever with the exception } catch (IOException e) { //do something clever with the exception } }

If the reader.read() method call throws an IOException, the following System.out.println((char) i ); is not executed. Neither is the last reader.close() or the System.out.println(“— File End —“); statements. Instead the program skips directly to the catch(IOException e){ … } catch clause. If the new FileReader(“someFile”); constructor call throws an exception, none of the code inside the try-block is executed.

Throwing Exceptions

If a method needs to be able to throw an exception, it has to declare the exception(s) thrown in the method signature, and then include a throw-statement in the method. Here is an example:

public int divide(int numberToDivide, int numberToDivideBy) throws BadNumberException{ if(numberToDivideBy == 0){ throw new BadNumberException(“Cannot divide by 0”); } return numberToDivide / numberToDivideBy; }

When an exception is thrown the method stops execution right after the “throw” statement. Any statements following the “throw” statement are not executed. In the example above the “return numberToDivide / numberToDivideBy;” statement is not executed if a BadNumberException is thrown. The program resumes execution when the exception is caught somewhere by a “catch” block. Catching exceptions is explained later.

You can throw any type of exception from your code, as long as your method signature declares it. You can also make up your own exceptions. Exceptions are regular Java classes that extends java.lang.Exception, or any of the other built-in exception classes. If a method declares that it throws an exception A, then it is also legal to throw subclasses of A.

A JAVA EXCEPTION HAS OCCURED SERVER PROBLEM SOLVED 100 % WORKING ON WINDOWS 7,8,10
A JAVA EXCEPTION HAS OCCURED SERVER PROBLEM SOLVED 100 % WORKING ON WINDOWS 7,8,10

The throw keyword

The

throw

statement allows you to create a custom error.

The

throw

statement is used together with an exception type. There are many exception types available in Java:

ArithmeticException

,

FileNotFoundException

,

ArrayIndexOutOfBoundsException

,

SecurityException

, etc:

Example

Throw an exception if age is below 18 (print “Access denied”). If age is 18 or older, print “Access granted”:


public class Main { static void checkAge(int age) { if (age < 18) { throw new ArithmeticException("Access denied - You must be at least 18 years old."); } else { System.out.println("Access granted - You are old enough!"); } } public static void main(String[] args) { checkAge(15); // Set age to 15 (which is below 18...) } }

The output will be:


Exception in thread "main" java.lang.ArithmeticException: Access denied - You must be at least 18 years old.at Main.checkAge(Main.java:4)at Main.main(Main.java:12)

If age was 20, you would not get an exception:

Example


checkAge(20);

The output will be:


Access granted - You are old enough!

In this article, we’ll explore all the possible combinations of try-catch-finally which may happen whenever an exception is raised and how the control flow occurs in each of the given cases.

  1. Control flow in try-catch clause OR try-catch-finally clause

    • Case 1: Exception occurs in try block and handled in catch block
    • Case 2: Exception occurs in try-block is not handled in catch block
    • Case 3: Exception doesn’t occur in try-block
  2. try-finally clause

    • Case 1: Exception occurs in try block
    • Case 2: Exception doesn’t occur in try-block

Control flow in try-catch OR try-catch-finally

1. Exception occurs in try block and handled in catch block: If a statement in try block raised an exception, then the rest of the try block doesn’t execute and control passes to the corresponding catch block. After executing the catch block, the control will be transferred to finally block(if present) and then the rest program will be executed.

  • Control flow in try-catch:

Java


class


GFG


public


static


void


main (String[] args)


int


[] arr =


new


int


];


try


int


i = arr[


];


System.out.println(


"Inside try block"


);


catch


(ArrayIndexOutOfBoundsException ex)


System.out.println(


"Exception caught in catch block"


);


finally


System.out.println(


"finally block executed"


);


System.out.println(


"Outside try-catch-finally clause"


);

Output

Exception caught in catch block
finally block executed
Outside try-catch-finally clause

2. Exception occurred in try-block is not handled in catch block: In this case, the default handling mechanism is followed. If finally block is present, it will be executed followed by the default handling mechanism.

Phiên giao dịch đầu năm Bulltrap - Rủi Ro hay Cơ Hội ?
Phiên giao dịch đầu năm Bulltrap – Rủi Ro hay Cơ Hội ?

try-catch-finally trong java

Khi chúng ta kết hợp try-catch-finally để xử lý các exception, chúng sẽ thực thi theo 3 trường hợp sau:

1, Nếu exception xảy ra bên trong try block thì luồng xử lý sẽ được chuyển tiếp cho catch block sau đó chuyển qua finally block và thực thi phần còn lại của method.

class Example { public static void main(String args[]) { int x = 0; int y = 10; try { int num = y / x; return; } catch (Exception ex) { System.out.println(“catch”); } finally { System.out.println(“finally”); } System.out.println(“next-statement: Outside of try-catch”); } }

Output:

catch

finallynext-statement: Outside of try-catch

2, Nếu không có exception được ném ra bên trong try block. Khối lệnh trong catch block sẽ được bỏ qua và tiến thẳng đến finally block sau đó thực thi phần còn lại của method.

class Example { public static void main(String args[]) { int x = 10; int y = 10; try { int num = y / x; } catch (Exception ex) { System.out.println(“catch”); } finally { System.out.println(“finally”); } System.out.println(“next-statement: Outside of try-catch”); } }

Output:

finally

next-statement: Outside of try-catch

3, Nếu gặp lệnh return trong khối try hoặc catch thì finally block vẫn được thực thi.

class Example { public static void main(String args[]) { try { return; } catch (Exception ex) { System.out.println(“catch”); } finally { System.out.println(“finally”); } System.out.println(“next-statement: Outside of try-catch”); } }

Output: finally

class Example { public static void main(String args[]) { try { int x = 0; int y = 10; int r = y/x; } catch (Exception ex) { return; } finally { System.out.println(“finally”); } System.out.println(“next-statement: Outside of try-catch”); } }

Output: finally

Note: Khối lệnh bên trong finally sẽ luôn được thực hiện trong bất kỳ tình huống nào.

How do I do a try except else in Java like I would in Python?

Example:


try: something() except SomethingException,err: print 'error' else: print 'succeeded'

I see try and catch mentioned but nothing else.

How do I do a try except else in Java like I would in Python?

Example:


try: something() except SomethingException,err: print 'error' else: print 'succeeded'

I see try and catch mentioned but nothing else.

I’m not entirely convinced that I like it, but this would be equivalent of Python’s else. It eliminates the problem’s identified with putting the success code at the end of the try block.


bool success = true; try { something(); } catch (Exception e) { success = false; // other exception handling } if (success) { // equivalent of Python else goes here }


catchblock, so you can just put the


elselogic after tye


try-catchaltogether. Jan 11, 2014 at 16:56


try-catch-elseconstruct, you should not use a finally block, as this will be executed even if there is a


returnor uncaught exception in the


tryblock. Just put the


if(success)block after the


try-catch.

What about this?


try { something(); } catch (Exception e) { // exception handling return; } // equivalent of Python else goes here

Sure, there are some cases where you want to put more code after the try/catch/else and this solution don’t fit there, but it works if it’s the only try/catch block in your method.

While Ryan’s answer of tracking errors with boolean(s) is nice, I think using a “logic block” to “skip forward” is better in this case.

In Java, you are allowed to create arbitrary context blocks (scopes) using

{...}


and assign labels to them. You can than call

break

Here is an example of what I mean that you can play with:


private static void trycatchelsetest(boolean err) { myLogicBlock: { try { System.out.println("TRY"); { //unlabeled block for demonstration if(err) throw new IOException("HELLO!"); } } catch(IOException e) { System.out.println("CATCH"); break myLogicBlock; } finally { System.out.println("FINALLY"); } System.out.println("ELSE"); } System.out.println("END"); }

The reason Try doesn’t have an else is because it is meant to catch a specific error from a specific block of code, which is either handled (usually by setting a default or returning), or bubbled up (and

finally

is offered only to make sure resources aren’t leaked because of the interrupt, even if you break out). In the break example above, we are handling the exception by skipping the block of code that is no longer relevant because of the error (skipping forward to the next logical step). The boolean example by Ryan handles it by noting the error happened, and letting latter parts of the code react to it happening after the fact.

I think the logic block is better than the boolean approach (as long as you have no complex logic based on what errors have been thrown) because it doesn’t require the reader to know the entire function to understand what happens. They see

break

and know that the program will effectively skip forward to the end of that block. The boolean requires the programmer to track down everything that makes decisions on it.

Obviously, “Skip-forward” and Boolean tracking each have their own advantages, and will usually be more a style choice.

While there is no built-in way to do that exact thing. You can do something similar to achieve similar results. The comments explain why this isn’t the exact same thing.

If the execution of the

somethingThatCouldError()

passes,

YAY!!

will be printed. If there is an error,

SAD

will be printed.


try { somethingThatCouldError(); System.out.println("YAY!!"); // More general, code that needs to be executed in the case of success } catch (Exception e) { System.out.println("SAD"); // code for the failure case }

This way is a little less explicit than Python. But it achieves the same effect.


Yayto the bottom of the


try.


somethingThatCouldError()does not throw an exception. I don't think that's exactly what Greg wanted. Aug 13, 2010 at 15:33


try-except-else: it will also catch


Exceptionfrom what is the "else" block;


try-except-elsedoes not do that, nor does the solution in Ryan's answer. In addition to not being equivalent, this also goes agaist the principle that


try-catchshould only be around as small a block of code as possible. Jan 11, 2014 at 16:54

Java Exceptions – Try…Catch

Merging ANYTHING Together... in Infinite Craft
Merging ANYTHING Together… in Infinite Craft

Java


class


GFG


public


static


void


main (String[] args)


int


[] arr =


new


int


];


try


int


i = arr[


];


System.out.println(


"Inside try block"


);


finally


System.out.println(


"finally block executed"


);


System.out.println(


"Outside try-finally clause"


);

Output :

finally block executed
Exception in thread “main” java.lang.ArrayIndexOutOfBoundsException: 4
at GFG.main(GFG.java:11)

2. Exception not raised: If an exception does not occur in the try block then the control flow will be finally block followed by the rest of the program

What are Exceptions?

Exceptions are events that occur during the execution of a program that disrupt its normal flow. They can be caused by various reasons, such as incorrect user input, insufficient resources, or bugs in the code. In Java, exceptions are represented as objects derived from the

Throwable

class, with the two main subclasses being

Error

and

Exception

.

[FULL] Khóa Học Java Cơ Bản Từ A tới Z cho Beginner | Học Java Từ Số 0 với Hỏi Dân IT
[FULL] Khóa Học Java Cơ Bản Từ A tới Z cho Beginner | Học Java Từ Số 0 với Hỏi Dân IT

Java


class


GFG


public


static


void


main (String[] args)


int


[] arr =


new


int


];


try


int


i = arr[


];


System.out.println(


"Inside try block"


);


catch


(NullPointerException ex)


System.out.println(


"Exception has been caught"


);


finally


System.out.println(


"finally block executed"


);


System.out.println(


"Outside try-catch-finally clause"


);

Output :

finally block executed

Run Time error:

Exception in thread “main” java.lang.ArrayIndexOutOfBoundsException: 4
at GFG.main(GFG.java:12)

3. Exception doesn’t occur in try-block: In this case catch block never runs as they are only meant to be run when an exception occurs. finally block(if present) will be executed followed by rest of the program.

Try-Except-Else-Finally in Python


def division(a, b): try: result = a / b except ZeroDivisionError: print("Error: Cannot divide by zero.") result = None except TypeError as e: print(f"Error: {e}") result = None else: print("Division successful.") finally: print("This part is executed irrespective of the exception") return result # Test runs: num_1 = 10 num_2 = 2 result_1 = division(num_1, num_2) print(f"Result 1: {result_1}\n") num_3 = 10 num_4 = 0 result_2 = division(num_3, num_4) print(f"Result 2: {result_2}")

Output:


Division successful. This part is executed irrespective of the exception Result 1: 5.0 Error: Cannot divide by zero. This part is executed irrespective of the exception Result 2: None

In the above example, the

division()

function takes two arguments and and tries to divide number by . The code which might raise an exception is kept inside the

try

block. In this scenario, it might raise a

ZeroDivisionError

if is zero or a

TypeError

if is

not a numeric type

.

Specific exceptions are caught using the

except

blocks. The corresponding

except

block will be executed if an exception arises inside the try block, preventing the application from crashing. If there are no exceptions, the

else

block will run, and the

finally

block will always run whether an exception occurred or not.

The BEST Meta Warlock Builds | Phase 2 | Season of Discovery
The BEST Meta Warlock Builds | Phase 2 | Season of Discovery

try – catch trong java

Trong khối try-catch sẽ có 2 trường hợp xảy ra:

  • Xuất hiện exception
  • Không xuất hiện exception

Khi exception không xuất hiện

Khi khối lệnh bên trong try không ném bất kỳ một exception nào thì khối lệnh bên trong catch sẽ không được thực hiện. Hay nói cách khác là khối lệnh bên trong catch sẽ xử lý khi có exception xảy ra.

class Example { public static void main(String args[]) { int x = 10; int y = 10; try { int num = x / y; System.out.println(“next-statement: Inside try block”); } catch (Exception ex) { System.out.println(“Exception”); } System.out.println(“next-statement: Outside of try-catch”); } }

Output

next-statement: Inside try block

next-statement: Outside of try-catch

Khi exception xuất hiện

Khi có một exception bên trong khối lệnh try được ném ra thì khối lệnh trong catch sẽ được thực hiện nhầm xử lý các exception.

class Example { public static void main(String args[]) { int x = 0; int y = 10; try { int num = y / x; System.out.println(“next-statement: Inside try block”); } catch (Exception ex) { System.out.println(“Exception Occurred”); } System.out.println(“next-statement: Outside of try-catch”); } }

Output:

Exception Occurred

next-statement: Outside of try-catch

Try-Catch-Finally in Java


public class Test { public static void main(String[] args) { int[] numbers = { 12, 5, 0 }; try { int result = numbers[0] / numbers[1]; System.out.println("Division successful. Result: " + result); // Accessing an index out of range System.out.println("Element at index 20: " + numbers[20]); } catch (ArithmeticException e) { System.out.println("Error: Cannot divide number zero."); } catch (ArrayIndexOutOfBoundsException e) { System.out.println("Error: Index is out of range."); } finally { System.out.println("This part is executed irrespective of the exception"); } } }

Output:


Division successful. Result: 2 Error: Index is out of range. This part is executed irrespective of the exception

In the above Java code, the

try

block contains the code that may raise exceptions. The program attempts to divide

numbers[0]

by

numbers[1]

and also tries to access an index that is out of range,

(numbers[20])

.

The

catch

blocks are used to catch specific exceptions that might occur in the

try

block. In this scenario, there are different catch blocks. One for

ArithmeticException

, which handles division by zero, and another for

ArrayIndexOutOfBoundsException

, which handles the attempt to access an index that is out of range for the array.

The

finally

block is used to specify code that will be executed irrespective of whether an exception occurred or not. It’s commonly used for cleanup tasks or releasing resources.

Skyblock but its raft..
Skyblock but its raft..

Propagating Exceptions

You don’t have to catch exceptions thrown from other methods. If you cannot do anything about the exception where the method throwing it is called, you can just let the method propagate the exception up the call stack to the method that called this method. If you do so the method calling the method that throws the exception must also declare to throw the exception. Here is how the callDivide() method would look in that case.

public void callDivide() throws BadNumberException{ int result = divide(2,1); System.out.println(result); }

Notice how the try-catch block is gone, and the callDivide method now declares that it can throw a BadNumberException. The program execution is still interrupted if an exception is thrown from the divide method. Thus the “System.out.println(result);” method will not get executed if an exception is thrown from the divide method. But now the program execution is not resumed inside the callDivide method. The exception is propagated to the method that calls callDivide. Program execution doesn’t resume until a catch-block somewhere in the call stack catches the exception. All methods in the call stack between the method throwing the exception and the method catching it have their execution stopped at the point in the code where the exception is thrown or propagated.

Java


class


GFG


public


static


void


main (String[] args)


try


String str =


"123"


int


num = Integer.parseInt(str);


System.out.println(


"Inside try block"


);


finally


System.out.println(


"finally block executed"


);


System.out.println(


"Outside try-finally clause"


);

Output

Inside try block
finally block executed
Outside try-finally clause

Related Articles:

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Mục lục

Trong bài viết này chúng ta sẽ cùng nhau tìm hiểu về cách kết hợp try-catch-finally để xử lý khi có một exception được ném ra.

try-catch luôn đi chung với nhau để xử lý exception ngoài ra chúng có thể kết hợp thêm finally khi cần thiết. Để hiễu rõ hơn chúng ta sẽ đi qua từng phần bên dưới.

try, catch, finally, throw - error handling in JavaScript
try, catch, finally, throw – error handling in JavaScript

Java


class


GFG


public


static


void


main (String[] args)


try


String str =


"123"


int


num = Integer.parseInt(str);


System.out.println(


"Inside try block"


);


catch


(NumberFormatException ex)


System.out.println(


"catch block executed..."


);


System.out.println(


"Outside try-catch clause"


);

Output

Inside try block
Outside try-catch clause

The Call Stack Explained

This text refers to the concept the “call stack” in several places. By the call stack is meant the sequence of method calls from the current method and back to the Main method of the program. If a method A calls B, and B calls C then the call stack looks like this:

A B C

When method C returns the call stack only contains A and B. If B then calls the method D, then the call stack looks like this:

A B D

Understanding the call stack is important when learning the concept of exception propagation. Exception are propagated up the call stack, from the method that initially throws it, until a method in the call stack catches it. More on that later.

Nesting \
Nesting \”If Statements\” Is Bad. Do This Instead.

Example: Propagating IOException’s

This code is a version of the previous method that throws the exceptions instead of catching them:

public void openFile() throws IOException { FileReader reader = new FileReader(“someFile”); int i=0; while(i != -1){ i = reader.read(); System.out.println((char) i ); } reader.close(); System.out.println(“— File End —“); }

If an exception is thrown from the reader.read() method then program execution is halted, and the exception is passed up the call stack to the method that called openFile(). If the calling method has a try-catch block, the exception will be caught there. If the calling method also just throws the method on, the calling method is also interrupted at the openFile() method call, and the exception passed on up the call stack. The exception is propagated up the call stack like this until some method catches the exception, or the Java Virtual Machine does.

Finally

You can attach a finally-clause to a try-catch block. The code inside the finally clause will always be executed, even if an exception is thrown from within the try or catch block. If your code has a return statement inside the try or catch block, the code inside the finally-block will get executed before returning from the method. Here is how a finally clause looks:

public void openFile(){ FileReader reader = null; try { reader = new FileReader(“someFile”); int i=0; while(i != -1){ i = reader.read(); System.out.println((char) i ); } } catch (IOException e) { //do something clever with the exception } finally { if(reader != null){ try { reader.close(); } catch (IOException e) { //do something clever with the exception } } System.out.println(“— File End —“); } }

No matter whether an exception is thrown or not inside the try or catch block the code inside the finally-block is executed. The example above shows how the file reader is always closed, regardless of the program flow inside the try or catch block.

Note: If an exception is thrown inside a finally block, and it is not caught, then that finally block is interrupted just like the try-block and catch-block is. That is why the previous example had the reader.close() method call in the finally block wrapped in a try-catch block:

} finally { if(reader != null){ try { reader.close(); } catch (IOException e) { //do something clever with the exception } } System.out.println(“— File End —“); }

That way the System.out.println(“— File End —“); method call will always be executed. If no unchecked exceptions are thrown that is. More about checked and unchecked in a later chapter.

You don’t need both a catch and a finally block. You can have one of them or both of them with a try-block, but not none of them. This code doesn’t catch the exception but lets it propagate up the call stack. Due to the finally block the code still closes the filer reader even if an exception is thrown.

public void openFile() throws IOException { FileReader reader = null; try { reader = new FileReader(“someFile”); int i=0; while(i != -1){ i = reader.read(); System.out.println((char) i ); } } finally { if(reader != null){ try { reader.close(); } catch (IOException e) { //do something clever with the exception } } System.out.println(“— File End —“); } }

Notice how the catch block is gone.

Spring Boot Tutorial | How To Handle Exceptions
Spring Boot Tutorial | How To Handle Exceptions

What Are the Differences Between Try-Catch and Try-Except?

Besides the syntax difference in how you write each, there is also an additional

else

code block available in Python that is different.

Python


  • try

    : Code that might cause an exception.

  • except

    : Code that handles the exception.

  • else

    : Code that runs if the try block does not raise an exception.

  • finally

    : Code that always runs, whether an exception occurred or not.

Java


  • try

    : Code that might cause an exception.

  • catch

    : Code that handles the exception.

  • finally

    : Code that always runs, whether an exception occurred or not.

Java does not have a direct equivalent to Python’s

else

block. The

finally

block in both cases is always executed regardless of whether an exception was thrown or not. Yet only in Python can you have code that runs if no exception occurs.

The

else

and

finally

blocks in both Python and Java are optional.

Let’s take a look at several examples.

Keywords searched by users: java try catch else

Java Try Catch Finally (With Examples) - Howtodoinjava
Java Try Catch Finally (With Examples) – Howtodoinjava
Try Catch Finally Block In Java | Learn Coding - Youtube
Try Catch Finally Block In Java | Learn Coding – Youtube
Handling Exceptions In Java: Try & Catch | Study.Com
Handling Exceptions In Java: Try & Catch | Study.Com
Java Try Catch Block With Example - Scientech Easy
Java Try Catch Block With Example – Scientech Easy
Error Handling,
Error Handling, “Try…Catch”
Nested Try In Java | Nested Try Catch Java - Scientech Easy
Nested Try In Java | Nested Try Catch Java – Scientech Easy
Try, Catch And Finally Block In Java | Exception Handling - Part 2 - Simple  Snippets
Try, Catch And Finally Block In Java | Exception Handling – Part 2 – Simple Snippets
Java Try-Catch - Javatpoint
Java Try-Catch – Javatpoint
Java Finally Block Try Catch Finally Exception Handling In Java 2 Java  Tutorial 37 - Youtube
Java Finally Block Try Catch Finally Exception Handling In Java 2 Java Tutorial 37 – Youtube
Try Catch Finally Block In Java | Learn Coding - Youtube
Try Catch Finally Block In Java | Learn Coding – Youtube
Finally Block In Java - Dinesh On Java
Finally Block In Java – Dinesh On Java

See more here: kientrucannam.vn

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