JDK, JRE, and JVM | What is JDK?

What is JDK?, What is JRE?, and What is JVM?. To find answer to these questions is necessary for all Java developers. JDK, JRE, and JVM are tools and libraries that are needed to compile and execute Java programs or applications. Once you install Java, all these tools and libraries get installed in your system which you can use for the development and execution of your programs. Below given image is showing all the tools and libraries that are required to run a Java program.

In our previous article, we discussed the Java compilation process. 

                                  

What is JDK?

JDK stands for Java development kit. As the name itself suggest, JDK helps the programmer in the development(from compilation to execution) of programs or applications. It's a group of libraries and tools needed for the compilation and execution of Java programs.

The JDK is a superset of the JRE, which means it contains JRE in itself. Apart from JRE, it includes some other tools also for developing, debugging, and monitoring Java applications. Some of the important tools are Java (Java application launcher), javac(java compiler), javap(java disassembler), Javadoc (java documentation tool), etc.

JDK exists physically on the computer. If Java is installed on your computer, you can see the JDK in the Java installation directory.

JDK = JRE + JVM + Development Tools(java,javac,javap,Javadoc etc.)

What is JRE?

According to Java, JRE stands for Java runtime environment. JRE comes into the picture as soon as you started running your program using the Java command. JRE contains JVM, class libraries, and other supporting files. JRE does not contain tools and utilities such as a compiler, or debugger for developing applets and applications.

The JRE is a superset of the JVM, which means it contains the JVM in itself. Apart from JVM it also contains runtime libraries that are needed to run the program. JVM which runs the program, uses these runtime libraries to execute the program and generate the output.

JRE also exists physically in your system. If Java is installed on your computer, you can see the JRE in the Java installation directory. It exists inside the JDK directory. Current downloads of JDK provide a jre parallel to jdk as well.

JRE = JVM + runtime libraries(contains packages like util, math, lang etc.)+ runtime files

What is JVM?

JVM stands for Java virtual machine. A virtual machine that is responsible for loading and executing the Java programs in memory. It also loads all the dependent classes of the running class in memory. JVM provides memory to objects and variables of a class.

As soon as you run a program by using the java command, a separate JVM is created which has some default size of memory available for classes, objects, variables etc. It loads code i.e. .class files in memory. It also verifies code the byte-code. Then converts bytecode into specific machine code. It provides a runtime environment and makes the availability of dependent classes and libraries. It also executes the code and generates the output. It also manages memory for classes, objects, etc. by using garbage collection.

Differences Between JDK, JVM, and JRE

JDK vs. JVM

JDK and JVM serve different purposes in Java development. JDK is primarily used by developers for writing and compiling Java code, while JVM is responsible for executing the compiled bytecode. The JDK includes the JVM, but JVM can exist independently without the presence of the JDK.

JDK vs. JRE

JDK and JRE also have distinct roles. JDK is a complete development environment that includes the necessary tools and libraries for creating Java applications. On the other hand, JRE is a runtime environment that only includes the components required to run Java programs but lacks the development tools present in JDK.

JRE vs. JVM

While JRE and JVM share the Java Virtual Machine, they differ in their functionalities. JRE includes the JVM along with other runtime components and class libraries, enabling it to execute Java applications. In contrast, JVM focuses solely on executing Java bytecode and managing the runtime environment.

 

Short Questions

Q: Is JDK required to run Java applications?

A: No, the JDK is only necessary for developers who need to write, compile, and test Java code. End-users can run Java applications using the JRE.

Q: Can I install multiple JDK versions on my system?

A: Yes, you can install multiple JDK versions on your system. However, ensure that you properly configure the environment variables to use the desired JDK version.

Q: Is JVM specific to Java?

A: Yes, the JVM is specific to Java and serves as the runtime environment for executing Java bytecode. Other languages, such as Kotlin and Scala, also target the JVM.

Q: Can I use JRE instead of JDK for development?

A: While it's possible to write simple Java programs using only the JRE, the JDK provides essential development tools and libraries that greatly enhance the development experience. It is recommended to use the JDK for Java development.

Q: How does the JVM handle memory management?

A: The JVM's garbage collector automatically manages memory allocation and deallocation. It tracks unused objects and frees up memory, ensuring efficient memory usage in Java applications.

Q: Are JDK, JVM, and JRE backward compatible?

A: Yes, Java aims to maintain backward compatibility. Newer versions of JDK, JVM, and JRE are designed to support applications developed using previous versions, ensuring smooth migration and compatibility.

In this article, we have discussed what is JDK. What is JVM and What is JRE. Firstly we explore each and then find the difference between them, All of these three are important parts of the Java environment.