What is the difference between JDK, JRE, and JVM?
JDK, JRE, and JVM are all key components of Java programming, but they serve different purposes in the Java development and execution process:
1. JDK (Java Development Kit):
- Purpose: JDK is a software development kit used to develop Java applications.
- Components:
- Compiler: Converts Java source code (.java files) into bytecode (.class files).
- Java Standard Library: A vast collection of pre-built classes and methods for common programming tasks.
- Debugger: Helps in finding and fixing bugs in the Java code.
- Other Development Tools: Profilers, javadoc (for generating documentation), etc.
- Usage: Developers use JDK to write, compile, and debug Java applications.
2. JRE (Java Runtime Environment):
- Purpose: JRE is an environment in which Java applications are run.
- Components:
- JVM (Java Virtual Machine): Executes Java bytecode.
- Java Standard Library: Necessary for running Java applications.
- Usage: End-users who only need to run Java applications (not develop them) require JRE. It includes the JVM and Java standard library.
3. JVM (Java Virtual Machine):
- Purpose: JVM is an abstract computing machine that enables a computer to run a Java program.
- Functionality:
- Class Loader: Loads class files into memory.
- Bytecode Verifier: Checks the bytecode for violations of access control and other security aspects.
- Interpreter: Interprets the bytecode line by line and executes the program.
- Just-In-Time (JIT) Compiler: Compiles parts of the bytecode that are frequently executed into native code for faster execution.
- Garbage Collector: Manages memory by deallocating objects that are no longer in use.
- Usage: JVM is included in both JDK and JRE. It executes Java applications by interpreting or compiling Java bytecode into machine code.
In summary, JDK is for Java development (writing, compiling, and debugging code), JRE is for running Java applications (it includes JVM), and JVM is the virtual machine that executes Java bytecode. When you develop Java applications, you need JDK. When you want to run Java applications, you need JRE, which includes the JVM.