JDK, JRE and JVM

The JDK, JRE, and JVM are essential components in the Java ecosystem, and they play different roles in the execution and development of Java applications:

1. JVM (Java Virtual Machine):

• The JVM is a virtual machine that allows Java applications to run on various hardware and software platforms. It provides an execution environment for Java bytecode, the intermediate code generated during the compilation of Java source code.
• JVM interprets or compiles bytecode into native machine code specific to the host platform, allowing Java applications to execute independently of the underlying hardware and operating system.
• The JVM also manages memory, garbage collection, and other runtime tasks to ensure the proper execution of Java applications.
• Different implementations of the JVM are available, including Oracle HotSpot, OpenJ9, and GraalVM.

1. JRE (Java Runtime Environment):

• The JRE is a subset of the Java Development Kit (JDK) that includes the necessary runtime components required to execute Java applications.
• It includes the JVM, class libraries, and other files and configurations that are essential for running Java applications.
• The JRE is what end-users typically need to run Java applications on their computers. It does not include the development tools and compiler that developers use.

1. JDK (Java Development Kit):

• The JDK is a comprehensive package that provides all the tools and resources needed for Java application development.
• It includes the JRE, the JVM, a compiler (usually javac), debugging tools, development libraries, and other utilities.
• Developers use the JDK to write, compile, and debug Java code. It is essential for creating Java applications.

In summary:

• JVM is the runtime environment that executes Java applications. It converts Java bytecode into machine code and manages memory and execution.
• JRE is a runtime environment that includes the JVM and libraries, suitable for running Java applications but not for development.
• JDK is a development kit that includes the JRE and additional tools, making it the complete package for developing, compiling, and running Java applications.

The Java developers use the JDK for development and testing, while end-users require the JRE to run Java applications on their machines. The JVM is an integral part of both the JRE and JDK, responsible for executing Java bytecode.