The Java Virtual Machine (JVM) is an abstract computing machine that enables a computer to run Java programs and programs written in other languages compiled to Java bytecode.
Purpose of the JVM
- Platform Independence (Write Once, Run Anywhere)
- Java code is compiled into an intermediate form called bytecode (.class files) rather than native machine code.
- This bytecode can be executed on any device that has a compatible JVM, making Java programs highly portable across different operating systems.
- Memory Management
- The JVM automatically manages memory through garbage collection (GC), which removes unused objects from memory to prevent memory leaks.
- Execution of Java Bytecode
- The JVM interprets or compiles Java bytecode into machine-specific code for execution.
- Uses techniques like Just-In-Time (JIT) Compilation to optimize performance by converting bytecode into native machine code at runtime.
- Security
- The JVM runs Java applications within a sandbox environment, preventing direct access to system resources unless explicitly allowed.
- It performs bytecode verification before execution to detect any malicious or unsafe code.
- Exception Handling
- Provides built-in mechanisms for handling exceptions, ensuring robust error management and program stability.
- Multi-threading Support
- The JVM provides a sophisticated thread model that allows applications to run multiple threads simultaneously, utilizing available system resources efficiently.
Components of the JVM
- Class Loader Subsystem – Loads Java class files (.class) into memory.
- Runtime Memory Areas – Includes heap, stack, method area, program counter register, and native method stack.
- Execution Engine – Responsible for interpreting or compiling bytecode into native machine instructions.
- Garbage Collector (GC) – Manages memory by automatically reclaiming unused objects.
- Native Interface (JNI – Java Native Interface) – Allows Java code to interact with native applications written in C/C++.
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