Jdk And Jre And Jvm | Tìm Hiểu Jvm

Why use JRE?

Here are the important reasons of using JRE:

• JRE contains class libraries, JVM, and other supporting files. It does not contain any tool for Java development like a debugger, compiler, etc.
• It uses important package classes like math, swingetc, util, lang, awt, and runtime libraries.
• If you have to run Java applets, then JRE must be installed in your system.

How JRE Functions?

JRE has an instance of JVM with it, library classes, and development tools. Once you write and compile Java code, the compiler generates a class file having byte code.

Here are the important components of JRE:

• Class loaders: The class loader loads various classes that are necessary for running a Java program. JVM uses three class loaders called the bootstrap class loader, extensions class loader, and system class loader.
• Byte code verifier: Byte code verifier verifies the bytecode so that the code doesn’t disturb the interpreter.
• Interpreter: Once the classes get loaded, and the code is verified, the interpreter reads the code line by line.
• Run-time: Run-time is a system used mainly in programming to describe time period during which a particular program is running.
• Hardware: Once you compile Java native code, it runs on a specific hardware platform.

In this way, the Java program runs in JRE.

Java Development Kit (JDK)

Java JDK is the software bundle using which the Java applications can be developed. JDK’s main component is the Java compiler using which the Java source code is compiled to byte code. Along with the Java compiler it contains more tools like Jar, JConsole, Javaw, etc. These help tools help in various different aspects of developing a Java application. The JDK bundle can be downloaded from the above given link in Oracle’s website.

Runtime Enviroment là gì?

Một chương trình phần mềm cần phải thực thi và để thực hiện nó cần một môi trường để chạy. Runtime Enviroment tải các tệp lớp và đảm bảo có quyền truy cập vào bộ nhớ và các tài nguyên hệ thống khác để chạy chúng. Trước đây, hầu hết các phần mềm đều sử dụng hệ điều hành (HĐH) làm Runtime Enviroment. Chương trình chạy bên trong bất kỳ máy tính nào được bật, nhưng dựa vào cài đặt hệ điều hành để truy cập tài nguyên. Tài nguyên trong trường hợp này sẽ là những thứ như bộ nhớ và tệp chương trình và dependencies. Java Runtime Enviroment đã thay đổi tất cả, ít nhất là đối với các chương trình Java.

JRE chứa các thư viện và phần mềm mà các chương trình Java của bạn cần chạy. Ví dụ, trình tải lớp Java là một phần của Java Runtime Environment. Phần mềm quan trọng này tải mã Java được biên dịch vào bộ nhớ và kết nối mã với các thư viện lớp Java thích hợp.

What is JVM?

JVM is an engine that provides a runtime environment to drive the Java Code or applications. It converts Java bytecode into machine language. JVM is a part of Java Run Environment (JRE). It cannot be separately downloaded and installed. To install JVM, you need to install JRE. The full form of JVM is Java Virtual Machine.

In many other programming languages, the compiler produces machine code for a specific system. However, Java compiler produces code for a virtual machine which is called as JVM.

JDK & JRE distributions

Java is maintained by Oracle, who offer their own approved JDK. But many other organisations offer JDK builds.

Here’s a summary of some of the most popular, specifically for the current long term support (LTS) Java 17.

JDK Build	Organisation	JRE available	Free commercial use
Oracle JDK	Oracle	✅ (NFTC license)
Oracle OpenJDK	Oracle	✅ (GNU license)
Amazon Corretto	Amazon	✅ (for Amazon Linux 2)	✅ (GNU license)
Eclipse Temurin by Adoptium	Eclipse	✅ (Eclipse license)

Interestingly, even though Oracle used to offer a JRE for earlier Java releases, that’s no longer the case. How come?

jlink signals the end of pre-built JREs

Well, JDK 9 adds a new tool called

jlink

to go alongside the new Platform Module System.

jlink

lets you build your own minimal JRE with only the required libraries, saving on storage and offering improved performance over the pre-built JREs that came before.

Since it’s possible to build your own JRE, Oracle no longer saw a need to offer one. Other organisations like Amazon and Eclipse realised that some developers do still use pre-built JREs, so continue to offer it.

Java Runtime Environment (JRE)

JRE is the software environment where the compiled Java byte codes executes. JRE is the implementation of JVM it includes the code required for running the programs and native code. It contains the implementation of Java interpreter, garbage collector, class loader, java class libraries and related files. You can download the JRE separately or as a bundle along with JDK from Oracle’s website.

Features of JRE

Here are theimportant features of JRE:

• Java Runtime Environment is a set of tools using which the JVM actually runs.
• JRE contains deployment technology, including Java Web Start and Java Plug-in.
• Developers can easily run the source code in JRE, but he/she cannot write and compile the Java program.
• It includes integration libraries like Java Database Connectivity (JDBC), Remote Method Invocation (RMI), Java Naming and Directory Interface (JNDI), and more.
• JRE has JVM and Java HotSpot virtual machine client.

How JDK Functions?

Here are the important components of JDK:

• JDK and JRE: The JDK enables programmers to create core Java programs that can be run by the JRE, which included JVM and class libraries.
• Class Libraries: It is a group of dynamically loadable libraries that Java program can call at run time.
• Compilers: It is a Java program that accepts text file of developers and compiles into Java class file. It is the common form of output given by compiler, which contains Java byte code. In Java, the primary compiler is Javac.
• Debuggers: Debugger is a Java program that lets developers test and debug Java programs.
• JavaDoc: JavaDoc is documentation made by Sun Microsystems for the Java. JavaDoc can be used generating API documentation in HTML file from the source program

Conslusion

You now know the main differences between the Java Development Kit (JDK) and the Java Runtime Environment (JRE).

• JDK includes tools for development such as compiler

• JRE is for running Java applications only

• JDK includes JRE for convenience

You also saw practically how to compile code with the JDK and run it with the JRE.

Have a question on this topic? I’m always looking for ways to improve this article, so leave a comment below and I’ll get back to you ASAP.

JDK vs JRE vs JVM in Java – Difference Between Them

Why use JDK?

Here are the important reasons of using JDK:

• JDK contains tools required to write Java programs, and JRE to execute them.
• It includes a compiler, Java application launcher, Appletviewer, etc.
• Compiler converts code written in Java into byte code.
• Java application launcher opens a JRE, loads the necessary class, and executes its main method.

Java Virtual Machine (JVM)

JVM is an abstract computing machine used to implement Java language. JVM is the key component in the Java eco system. Java’s important property is platform independence and to achieve that the role of JVM is critical. The JVM sits on top of the hardware and is used to execute the Java programs. Input for the JVM is Java byte code and it interprets the instructions in the byte code thus executing the programs.

Why JVM?

Here are the important reasons of using JVM:

• JVM provides a platform-independent way of executing Java source code.
• It has numerous libraries, tools, and frameworks.
• Once you run Java program, you can run on any platform and save lots of time.
• JVM comes with JIT(Just-in-Time) compiler that converts Java source code into low-level machine language. Hence, it runs more faster as a regular application.

JRE (Java Runtime Environment)

While the focus of the JDK is on developing Java applications, the JRE (Java Runtime Environment) is all about running them. It’s a library which you install on any machine you need to run Java programs.

What sort of library? Here’s what we see if we list of the contents of the JRE.


$ ls -l /C/Java/jdk-17.0.3+7-jre/ total 76 drwxr-xr-x 1 Tom 197121 0 Apr 20 00:13 bin/ drwxr-xr-x 1 Tom 197121 0 Apr 19 23:04 conf/ drwxr-xr-x 1 Tom 197121 0 Apr 19 23:04 legal/ drwxr-xr-x 1 Tom 197121 0 Apr 19 23:04 lib/ -rw-r--r-- 1 Tom 197121 2439 Apr 19 23:10 NOTICE -rw-r--r-- 1 Tom 197121 1592 Apr 19 23:10 release


This is the minimum set of files needed to run any Java application. The most important is

java.exe

inside the bin directory. Use the

java

command to execute Java application

.class

files.

When you do this, a JVM starts up to execute statements contained within

.class

files. So you can think of JRE as containing the JVM, but more accurately the JRE has the libraries to start the JVM.

What else is in the JRE?

Also in the JRE are many libraries that Java applications may rely on at runtime. You’ll probably be familiar with some of them, for example:

• 
java.util.*

  packages (e.g.
  
java.util.Map

  )
• 
java.lang.*

  packages (e.g.
  
java.lang.Integer

  )

But note that the JRE doesn’t include any of the development tools like

javac

and

jar

. That’s what the JDK is for. The JRE is only for running Java applications.

Let’s run something using the JRE

Let’s put the JRE to the test and get it running something!

Remember that we compiled

HelloWorld.java

into

HelloWorld.class

earlier using the JDK? Running it in the JRE is as simple as passing the class name to the

java

command.


$ /C/Java/jdk-17.0.3+7-jre/bin/java HelloWorld Hello world!


Awesome! We got the expected output. Every Java application starts here.

But when we run

java

there’s quite a lot happening in the background just to print a simple string:

1. a ClassLoader loads

   
.class

   files into the JVM, so it doesn’t need to know about the filesystem

2. the JVM executes classes and manages memory areas like the heap and stack

3. eventually the JVM interacts with native operating system libraries to execute commands

So we’ve compiled an application using the JDK and run it with the JRE. Are we all done here?

Hang on! There’s more to this story, since the JDK actually contains a JRE itself…

What is JRE?

JRE stands for Java Runtime Environment. It is a runtime environment that is used for running the java applications in our system. The JRE contains JVM (Java Virtual Machine) along with a set of libraries and utilities that are required in order to run java applications. When we try to execute a java application, a runtime environment is provided by the JRE that contains all the necessary components that are required by the application to execute.

Features of JRE:

• JRE is a collection of tools that helps in the execution of the JVM. It also provides a few deployment tools like Java Plug-in and Java Web Start.
• A user can run java code efficiently with only JRE. Unfortunately, JRE does not allow writing java programs.
• JRE also includes some integration libraries such as JDBC (Java Database Connectivity), JNDI (Java Naming and Directory Interface), RMI (Remote Method Invocation), and others.
• In addition to JVM, it also contains a virtual machine client for Java HotSpot.

Quản lý bộ nhớ trong java 8

Cho đến Java 8, metaspace được biết đến như là permgen. Bên cạnh việc là một cái tên hay hơn nhiều, metaspace là một thay đổi quan trọng đối với cách các nhà phát triển tương tác với không gian bộ nhớ của Java. Trước đây, bạn sẽ sử dụng lệnh * java -XX: MaxPermSize* để theo dõi kích thước của không gian permgen. Từ Java 8 trở đi, Java sẽ tự động tăng kích thước của metaspace để đáp ứng nhu cầu meta của chương trình của bạn. Java 8 cũng giới thiệu một cờ mới, MaxMetaspaceSize, có thể được sử dụng để giới hạn kích thước metaspace.

Các tùy chọn bộ nhớ khác, heap và stack, vẫn giữ nguyên trong Java 8.

Quản lí bộ nhớ trong JVM

Tương tác phổ biến nhất với JVM đang chạy là kiểm tra mức sử dụng bộ nhớ trong heap và stack. Điều chỉnh phổ biến nhất là điều chỉnh các cài đặt bộ nhớ của JVM.

Thu gom rác(Garbage collection)

Trước Java, tất cả bộ nhớ chương trình được quản lý bởi lập trình viên. Trong Java, bộ nhớ chương trình được quản lý bởi JVM. JVM quản lý bộ nhớ thông qua một quá trình gọi là bộ sưu tập rác(garbage collection), liên tục xác định và loại bỏ bộ nhớ không sử dụng trong các chương trình Java. Việc thu gom rác xảy ra bên trong một JVM đang chạy.

Bộ nhớ Java và JRE

Bộ nhớ Java bao gồm ba thành phần: heap, stack và metaspace (trước đây được gọi là permgen).

• Metaspace là nơi Java giữ thông tin không thay đổi của chương trình như các định nghĩa lớp.
• Không gian heap (Heap space) là nơi Java giữ nội dung biến(variable content).
• Không gian ngăn xếp (Stack space) là nơi Java lưu trữ thực thi hàm(function execution) và tham chiếu biến(variable references).

What is JDK?

JDK stands for Java Development Kit. It is a complete software environment for building applications using Java language. It contains a collection of tools and utilities which are very essential for a developer for writing, compiling, and debugging. The JDK is platform-dependent and because of this reason, it has different OS platform versions for Windows, Linux, Mac, and so on.

The JDK contains the Java Runtime Environment (JRE), which provides the Java Virtual Machine (JVM) for executing Java code. The JDK also contains the Java compiler, which converts our Java source code into Java bytecode that can be executed on any machine that has a compatible JVM in it. The JDK also offers a variety of tools for debugging, testing, and monitoring our Java applications.

Below listed are the features of JDK:

• JDK provides an environment for writing and running Java source code.
• JDK provides all the functionalities of JRE and JVM.
• JDK enables developers in handling exceptions smoothly by integrating many extensions together into a single catch block.
• It also provides a debugger, compiler, and other development tools.

Difference Between JDK, JRE and JVM

Here are the major differences between JDK vs. JRE vs. JVM:

JDK	JRE	JVM
The full form of JDK is Java Development Kit.	The full form of JRE is Java Runtime Environment.	The full form of JVM is Java Virtual Machine.
JDK is a software development kit to develop applications in Java.	It is a software bundle which provides Java class libraries with necessary components to run Java code.	JVM executes Java byte code and provides an environment for executing it.
JDK is platform dependent.	JRE is also platform dependent.	JVM is highly platform dependent.
It contains tools for developing, debugging, and monitoring java code.	It contains class libraries and other supporting files that JVM requires to execute the program.	Software development tools are not included in JVM.
It is the superset of JRE	It is the subset of JDK.	JVM is a subset of JRE.
The JDK enables developers to create Java programs that can be executed and run by the JRE and JVM.	The JRE is the part of Java that creates the JVM.	It is the Java platform component that executes source code.
JDK comes with the installer.	JRE only contain environment to execute source code.	JVM bundled in both software JDK and JRE.

Trong bài này, chúng ta sẽ tìm hiểu về JVM, JRE, JDK. Nó bao gồm những thành phần nào và nhiệm vụ của nó là gì?

JVM (Java Virtual Machine) là tạo ra môi trường máy ảo để thực thi mã java bytecode.

• Máy ảo Java là phần mềm giả lập máy tính, nó tập hợp các lệnh logic để xác định hoạt động của máy.
• Có thể xem nó như là một hệ điều hành thu nhỏ.
• JVM chuyển mã byte code thành machine code tùy theo môi trường tương ứng (gọi là khả năng khả chuyển)
• JVM cung cấp môi trường thực thi cho chương trình Java (gọi đó là khả năng độc lập với nền).

JVM có sẵn trong nhiều phần cứng và nền tảng phần mềm.

JVM gồm 4 nhiệm vụ chính: Load code, Verifies code, Executes code, Provides runtime enviroment.

JRE viết tắt Java Runtime Enviromement. Nó bao gồm các thư viện và các file mà JVM sử dụng lúc thực thi.

JDK viết tắt của Java Development Kit. Nó gồm JRE + công cụ phát triển.

Bộ công cụ JDK gồm các chương trình thực thi đáng chú ý sau:

• javac: Chương trình biên dịch các chương trình nguồn viết bằng ngôn ngữ java ra các tập tin thực thi được trên máy ảo Java.
• java: Một chương trình để dịch mã mà bạn viết thành mã bytecode, khi ứng dụng Java chạy nó dịch mã bytecode thành mã máy tính và thực thi, điều đó có nghĩa là bytecode chỉ là một mã trung gian.Đây là chương trình làm máy ảo của Java, thông dịch mã Bytecode của các chương trình kiểu application thành mã thực thi của máy thực.
• Archive (jar): Là một chương trình nén các file thành một file duy nhất có đuôi jar. Thường dùng để đóng gói các file class.
• Javadoc: Là một công cụ tạo ra tài liệu hướng dẫn sử dụng API.
• appletviewer: Bộ thông dịch, thực thi các chương trình kiểu applet.
• javadoc: Tạo tài liệu về chú thích chương trình nguồn một cách tự động.
• jdb: Trình gở rối.
• rmic: Tạo Stub cho ứng dụng kiểu RMI.
• rmiregistry: Phục vụ danh bạ (Name Server) trong hệ thống RMI

By Pankaj

While we believe that this content benefits our community, we have not yet thoroughly reviewed it. If you have any suggestions for improvements, please let us know by clicking the “report an issue“ button at the bottom of the tutorial.

The difference between JDK, JRE, and JVM is one of the popular interview questions. You might also be asked to explain JDK vs JRE vs JVM.

JDK, JRE, and JVM are core concepts of Java programming language. We don’t use these concepts in programming. But, as a Java developer, we should know about them.

Java Development Kit aka JDK is the core component of Java Environment and provides all the tools, executables, and binaries required to compile, debug, and execute a Java Program. JDK is a platform-specific software and that’s why we have separate installers for Windows, Mac, and Unix systems. We can say that JDK is the superset of JRE since it contains JRE with Java compiler, debugger, and core classes.

JVM is the heart of Java programming language. When we execute a Java program, JVM is responsible for converting the byte code to the machine-specific code. JVM is also platform-dependent and provides core java functions such as memory management, garbage collection, security, etc. JVM is customizable and we can use java options to customize it. For example, allocating minimum and maximum memory to JVM. JVM is called virtual because it provides an interface that does not depend on the underlying operating system and machine hardware. This independence from hardware and the operating system makes java program write-once-run-anywhere.

JRE is the implementation of JVM. It provides a platform to execute java programs. JRE consists of JVM, Java binaries, and other classes to execute any program successfully. JRE doesn’t contain any development tools such as Java compiler, debugger, JShell, etc. If you just want to execute a java program, you can install only JRE. You don’t need JDK because there is no development or compilation of java source code is required. Now that we have a basic understanding of JDK, JVM, and JRE, let’s look into the difference between them.

Let’s look at some of the important differences between JDK, JRE, and JVM.

Sometimes you will find JIT alongside JVM, JDK, and JRE in textbooks. JIT is part of the JVM that optimizes the process of converting byte code to machine-specific language. It compiles similar byte codes at the same time and reduces the overall time taken for the compilation of byte code to machine-specific language.

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Below text from this article – JVM is called virtual because it provides an interface that does not depend on the underlying operating system and machine hardware. This independence from hardware and the operating system is what makes java program write-once-run-anywhere. Does JVM provided interface not depend on underlying platform. If that interface (i.e. loding, linking, JIT, interpreter etc) is same for all platforms then why JVMs are different for each platform. I feel this interface which takes byte code as input and gives you end result is platform dependent which makes Java platform independent. May be you can correct my understanding.

– Love Gupta

Thanks a lot!

– Saangram

Please update the version of Java.

– srinivas narla

very well explained,

– Vitthal Kasbe

JVM is also platform dependent under JVM , i hope this is a TYPO.

– Sailendra

I wish to know step by step execution and impacts , functionalties for jdk, jvm (including memory areas )m jre ? I mean i wish to know end-to-end flow when a java program gets executed (specially through various section inside JVM – among those i also wish to know impacts on memory areas (heap,stack, native area ), class loaders e.t.c.

– Bibhu Prasad Tripathy

very good.

– Leandro

Hi Pankaj, Thanks for such useful tutorials. You are doing great. Keep it up. I have some doubt about JIT. You said that it optimizes byte code to machine specific language compilation by compiling similar byte codes at same time. My question is that while converting byte code into machine specific code do all the byte code passes through JIT. Because i have heared that only interpretor also have its role in converting byte code into machine specific code. Or only similar byte codes are passes through JIT and rest all passes through interpreter. It would be very useful if you can elaborate it with some example.

– debu

This is to just let you know that you could update regarding ‘Current JDK Version’ information.

– gansai

I’m confused when I go to Oracles site to download the JDK and they ask if you want JDK for Java EE or JDK for Java SE. What if I want to ability to develop both. Do I really have to install 2 separate JDKs?

– Mike

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Hiểu rõ sự khác nhau giữa JDK, JRE và JVM là điều khá quan trọng trong Java.

Nội dung chính

JDK (Java Development Kit)

The JDK (Java Development Kit) is a library which you download to your computer to help you develop Java applications.

What kind of library? Whether you use an installer, package manager, or zip file to setup the JDK, you end up with a directory structure like this.


$ ls -l /C/Java/jdk-17.0.2 total 128 drwxr-xr-x 1 Tom 197121 0 Dec 7 21:56 bin/ drwxr-xr-x 1 Tom 197121 0 Dec 7 21:56 conf/ drwxr-xr-x 1 Tom 197121 0 Dec 7 21:56 include/ drwxr-xr-x 1 Tom 197121 0 Dec 7 21:56 jmods/ drwxr-xr-x 1 Tom 197121 0 Dec 7 21:56 legal/ drwxr-xr-x 1 Tom 197121 0 Dec 7 21:56 lib/ -rw-r--r-- 1 Tom 197121 1241 Dec 7 21:56 release


What the heck is all this stuff? It’s a suite of juicy tools to help you do an awesome job as a Java developer.

The JDK bin directory

For example, in the bin directory are these programs:

• javac: compiles

  
.java

  source files into binary
  
.class

  files in bytecode format

• jar: creates a

  
.jar

  file archive from all your
  
.class

  files, for easy distribution

• javadoc: generates HTML documentation from your Java source files

There are in total 35 tools in the JDK bin directory, including JConsole, used to monitor Java applications. Have a look yourself and try running them!

Let’s compile something using the JDK

One of the most important tools in the JDK is

javac

. Without it you wouldn’t be able to compile your source code to later run using the JRE (more on that later).

Let’s try compiling this simple

HelloWorld.java

class using

javac

.


class HelloWorld { public static void main(String\[\] args) { System.out.println("Hello world!"); } }


We just pass the file name to

javac

and the compiler spits out a

.class

file.


$ ls HelloWorld.java $ /C/Java/jdk-17.0.3+7/bin/javac HelloWorld.java $ ls HelloWorld.class HelloWorld.java


And what’s so great about a

.class

file?

Well, it’s important to know that the JVM (Java Virtual Machine) receives instructions through bytecode (

.class

files) and NOT source files (

.java

) files. Bytecode has been optimised and compressed specifically for the JVM to run as fast as possible.

We’ll learn more about the JVM later when we use it to run our HelloWorld application.

JDK key facts

• it’s a set of tools for developing Java applications

• includes the javac compiler command to generate Java bytecode from source code

• has many other tools within bin directory (jar, javadoc etc.)

• install and use it on your development machine

• also use on Continuous Integration (CI) servers to build Java applications

Tìm hiểu JVM

JVM (viết tắt của Java Virtual Machine) là một thiết bị trừu tượng (ảo) có thể giúp máy tính chạy các chương trình Java. Nó cung cấp môi trường runtime mà trong đó Java Bytecode có thể được thực thi.

JVM là có sẵn cho nhiều nền tảng (Windows, Linux…). JVM, JRE và JDK là phụ thuộc nền tảng, bởi vì cấu hình của mỗi OS (hệ điều hành) là khác nhau. Nhưng, Java là độc lập nền tảng.

Các nhiệm vụ chính của JVM

• Tải code
• Kiểm tra code
• Thực thi code
• Cung cấp môi trường runtime

Cấu trúc của JVM

Trong đó:

• Classloader: Là một hệ thống con của JVM được sử dụng để tải class file.
• Class (method) Area: Lưu trữ cấu trúc mỗi lớp, chẳng hạn như hằng, trường, dữ liệu phương thức, code của phương thức, …
• Heap: Nó là khu vực dữ liệu runtime mà trong đó đối tượng được cấp phát.
• Stack: Stack trong Java lưu giữ các Frame. Nó giữ các biến cục bộ và các kết quả cục bộ, và thực hiện một phần nhiệm vụ trong phần triệu hồi và trả về phương thức. Mỗi Thread có một Stack riêng, được tạo tại cùng thời điểm với Thread.
  Một Frame mới được tạo mỗi khi một phương thức được triệu hồi và bị hủy khi lời triệu hồi phương thức là kết thúc.
• Program Counter Register: Nó chứa địa chỉ của chỉ lệnh JVM hiện tại đang được thực thi.
• Native Method Stack: Bao gồm tất cả các phương thức tự nhiện được sử dụng trong ứng dụng.
• Execution Engine: Phần này bao gồm:
  Một bộ xử lý ảo Virtual ProcessorMột trình thông dịch Interpreter. Đọc Bytecode Stream sau đó thực thi các chỉ thị.
• Just-In-Time (JIT) Compiler: được sử dụng để cải thiện hiệu suất. JIT biên dịch các phần của Bytecode mà có cùng tính năng tại cùng một thời điểm, và vì thế giảm lượng thời gian cần thiết để biên dịch. Ở đây khái niệm Compiler là một bộ biên dịch tập chỉ thị của JVM thành tập chỉ thị của một CPU cụ thể.

JDK & JRE similarities

Whaaat! There’s really a JRE inside the JDK? 🤔

Yes, there are quite a few similarities between the JDK and JRE, so let’s take a closer look.

JDK contains a JRE

When you download and install the Java Development Kit (JDK) not only do you have everything needed to compile Java applications, but also to run them too! Or in other words, the JDK contains the Java Runtime Environment (JRE).

If my name were Venn and not Tom, I’d illustrate the idea like this.

The JDK includes the JRE to make development as simple as possible. We can compile and run applications using one JDK installation, without any other downloads.

Let’s try compiling and running HelloWorld using only the JDK.


$ /C/Java/jdk-17.0.3+7/bin/javac HelloWorld.java $ /C/Java/jdk-17.0.3+7/bin/java HelloWorld Hello world!


Why use the JRE?

If the JDK already includes the JRE, wouldn’t you always use the JDK to compile and run applications?

Yes, it’s perfectly valid to install a JDK onto a production server and use it to run Java applications. But there are some special use cases to consider.

• size: the JRE is less than half the size of the JDK. Remember all those extra JDK development tools? If your target environment is a device with limited storage, install a JRE instead.

• security: given all the extra tooling packaged in the JDK, it’s more secure and clean not to make it available in production by instead using the JRE

To see for yourself, let’s compare the size of the JDK and JRE.


$ du -hs /C/Java/jdk-17.0.3+7 301M /C/Java/jdk-17.0.3+7 $ du -hs /C/Java/jdk-17.0.3+7-jre 124M /C/Java/jdk-17.0.3+7-jre


Using the

diff

command you can also check the differences between the JDK and JRE. From my investigation I see that the JDK contains 52 files that aren’t in the JRE! None of those are required for running Java applications.

Platform dependent

Both the JDK and JRE are platform dependent. That means you can only use a version that’s been built for the specific type of machine you’re using.

The JDK is available for:

• Windows

• MacOS

• Linux

The cool thing about Java is that the bytecode generated by the JDK’s compiler can be run anywhere that a JRE is available. This is the write once, run anywhere ethos of Java.

For example, you can compile Java source code on a Windows machine and run it on Linux. No problem.

What is JVM?

JVM stands for Java Virtual Machine, and it is a software component that allows your computer to run Java programs. When we write a Java program, it is compiled into bytecode. This bytecode can not execute on its own and requires JVM to run it.

The JVM has the responsibility of executing the bytecode and converting it into machine code that can be understood by the computer. The JVM also manages memory usage and performs garbage collection, which is the process of deallocating memory that is no longer needed by the program.

Listed below are some features of JVM

• JVM converts byte code into machine code which is understood by the computer.
• JVM provides fundamental Java functionalities such as management of memory, garbage collection, and so on.
• JVM uses libraries and files of JRE to run the java program.
• JVM is an essential component of JRE.
• It is capable of executing the java program line by line. Hence, it is also referred to as an interpreter.
• Primary functions of JVM includes program loading, linking, initialization, and compilation.

Features of JDK

Here are the important features of JDK:

• It enables you to handle multiple extensions in a single catch block.
• JDK includes all features that JRE has.
• It contains development tools such as a compiler, debugger, etc.
• JDK provides the environment to develop and execute Java source code.
• It can be installed on Windows, Unix, and Mac operating systems.
• Diamond operator can be used in specifying a generic type interface instead of writing the exact one.

How JVM Functions?

Here are the important components of JVM:

1) Class Loader

The class loader is a subsystem used for loading class files. It performs three major functions viz. Loading, Linking, and Initialization.

2) Method Area

JVM Method Area stores structure of class like metadata, the code for Java methods, and the constant runtime pool.

3) Heap

All the Objects, arrays, and instance variables are stored in a heap. This memory is shared across multiple threads.

4) JVM language Stacks

Java language Stacks store local variables, and its partial results. Each and every thread has its own JVM language stack, created concurrently as the thread is created. A new frame is created when method is invoked, and it is removed when method invocation process is complete.

5) PC Registers

PC registers store the address of the Java virtual machine instruction, which is currently executing. In Java, each thread has its separate PC register.

6) Native Method Stacks

Native method stacks hold the instruction of native code depends on the native library. It allocates memory on native heaps or uses any type of stack.

7) Execution Engine

It is a type of software that is used to test software, hardware, or complete systems. The test execution engine never carries any information about the tested product.

8) Native Method interface

The Native Method Interface is a programming framework. It allows Java code, which is running in a JVM to call by libraries and native applications.

9) Native Method Libraries

Native Libraries is a collection of the Native Libraries (C, C++), which are needed by the Execution Engine.

Difference Between JDK, JRE and JVM

After reading the above introduction of all three components, now we will go through the table below to see the head-to-head difference between JDK JRE and JVM.

JDK	JRE	JVM
JDK stands for Java Development Kit.	JRE stands for Java Runtime Environment.	JVM stands for Java Virtual Machine.
The Java Development Kit (JDK) is a software development kit that lets you build Java applications.	The Java Runtime Environment (JRE) is a software package that includes the Java Virtual Machine (JVM), class libraries, and other components required to run Java applications.	The Java Virtual Machine (JVM) is an abstract machine that provides an environment for Java ByteCode execution.
JDK includes tools for creating, monitoring, and debugging Java code.	JRE includes class libraries and other supporting files needed by JVM to run Java code.	JVM has no software development tools.
It is platform-dependent	It is also platform-dependent like JDK	It is platform-independent
The JDK mainly assists in code execution. Its primary purpose is development.	JRE is primarily tasked with creating an environment for code execution.	All implementations are specified by JVM. It is in charge of providing all of these implementations to the JRE.
JDK = Development Tools + JRE	JRE = Class libraries + JVM	JVM = provides a runtime environment.

ConclusionIn essence, comprehending the disparity between JDK, JRE, and JVM is crucial for any Java developer. The JDK encompasses the complete set of tools needed for Java development, including the JRE, whereas the JRE is an execution environment for running Java applications. On the other hand, the JVM is the runtime instance that executes Java bytecode. Together, these components form a cohesive ecosystem that facilitates Java programming, ensuring seamless development, deployment, and execution of Java applications across various platforms.

Difference Between JDK, JRE, and JVM

Parameter	JDK	JRE	JVM
Full-Form	The JDK is an abbreviation for Java Development Kit.	The JRE is an abbreviation for Java Runtime Environment.	The JVM is an abbreviation for Java Virtual Machine.
Definition	The JDK (Java Development Kit) is a software development kit that develops applications in Java. Along with JRE, the JDK also consists of various development tools (Java Debugger, JavaDoc, compilers, etc.)	The Java Runtime Environment (JRE) is an implementation of JVM. It is a type of software package that provides class libraries of Java, JVM, and various other components for running the applications written in Java programming.	The Java Virtual Machine (JVM) is a platform-independent abstract machine that has three notions in the form of specifications. This document describes the requirement of JVM implementation.
Functionality	The JDK primarily assists in executing codes. It primarily functions in development.	JRE has a major responsibility for creating an environment for the execution of code.	JVM specifies all of the implementations. It is responsible for providing all of these implementations to the JRE.
Platform Dependency	The JDK is platform-dependent. It means that for every different platform, you require a different JDK.	JRE, just like JDK, is also platform-dependent. It means that for every different platform, you require a different JRE.	The JVM is platform-independent. It means that you won’t require a different JVM for every different platform.
Tools	Since JDK is primarily responsible for the development, it consists of various tools for debugging, monitoring, and developing java applications.	JRE, on the other hand, does not consist of any tool- like a debugger, compiler, etc. It rather contains various supporting files for JVM, and the class libraries that help JVM in running the program.	JVM does not consist of any tools for software development.
Implementation	JDK = Development Tools + JRE (Java Runtime Environment)	JRE = Libraries for running the application + JVM (Java Virtual Machine)	JVM = Only the runtime environment that helps in executing the Java bytecode.
Why Use It?	Why use JDK? Some crucial reasons to use JDK are:	Why use JRE? Some crucial reasons to use JRE are:	Why use JVM? Some crucial reasons to use JVM are:
Features	Features of JDK	Features of JRE	Features of JVM Here are a few crucial features of JVM:

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The article goes through explaining Java Virtual Machine (JVM), Java Runtime Environment (JRE), and Java Development Kit (JDK) in detail. Moreover, it covers the differences between JVM, JRE, and JDK.

Ja

va is a popular programming language for developing various applications, from desktop software to web applications and mobile apps. When working with Java, you may come across the terms JDK, JRE, and JVM, all of which are important components of the Java ecosystem.

JDK, JRE, and JVM are three distinct components used to run Java applications, but they each serve a different purpose. Understanding the differences between these components is important for Java developers and anyone else who works with Java applications. This blog post will explore the differences between JDK, JRE, and JVM and explain why each component is important in Java development.

The article goes through explaining Java Virtual Machine (JVM), Java Runtime Environment (JRE), and Java Development Kit (JDK) in detail. Moreover, it covers the differences between JVM, JRE, and JDK.

Ja

va is a popular programming language for developing various applications, from desktop software to web applications and mobile apps. When working with Java, you may come across the terms JDK, JRE, and JVM, all of which are important components of the Java ecosystem.

JDK, JRE, and JVM are three distinct components used to run Java applications, but they each serve a different purpose. Understanding the differences between these components is important for Java developers and anyone else who works with Java applications. This blog post will explore the differences between JDK, JRE, and JVM and explain why each component is important in Java development.