JVM stands for Java Virtual Machine. It is an integral part(crucial component) of the Java Runtime Environment (JRE) and Java Development Kit (JDK). The JVM is responsible for executing Java bytecode(intermediate code), which is the compiled form of Java source code. It acts as an abstract machine that provides a runtime environment for executing Java bytecode.
When you write Java code, you use a Java compiler(translator) to convert the human-readable Java source code into platform-independent bytecode(0,1). This bytecode is not specific to any particular operating system or hardware architecture; instead, it is meant to be executed by the JVM.
Here’s how the JVM works:
Compilation: When you compile a Java source file (.java), the Java compiler (javac) converts it into bytecode (.class). This bytecode is a set of instructions that the JVM can understand.
Class Loading: The JVM’s class loader loads the bytecode into memory and performs various checks to ensure the bytecode is valid and doesn’t violate security restrictions. The JVM’s class loader subsystem loads classes and interfaces as they are referenced during program execution. It is responsible for locating the necessary binary data (class files) and linking it to the runtime representation.
Bytecode Execution: The JVM’s bytecode interpreter executes the bytecode instructions one by one. As the code is executed, it may be optimized by the Just-In-Time (JIT) compiler, which converts frequently executed bytecode into native machine code, resulting in improved performance. It verifies that the bytecode follows the Java language’s rules and adheres to the Java Virtual Machine Specification.
Runtime Environment: The JVM provides a runtime environment, including memory management, garbage collection, and security, which ensures that Java applications run securely and efficiently.
Platform Independence: One of the key advantages of the JVM is that it allows Java programs to be platform-independent. As long as a compatible JVM is available for the target platform, the same Java bytecode can run on any operating system or architecture without modification. The JVM interprets this bytecode and translates it into machine code, specific to the underlying operating system and hardware.
Just-In-Time (JIT) Compiler: To improve performance, the JVM often employs a Just-In-Time compiler. The JIT compiler translates bytecode into machine code at runtime, optimizing frequently executed code paths for better execution speed.
Memory Management: JVM (java virtual machine)manages memory allocation and garbage collection. It automatically handles memory allocation for objects and releases memory that is no longer in use through garbage collection.
By providing a consistent execution environment across different platforms, the JVM enables the “write once, run anywhere” (WORA) capability, a fundamental principle of Java’s “write once, run anywhere” philosophy.
It’s worth noting that there are different implementations of the JVM, each provided by different vendors, like Oracle HotSpot, OpenJ9, GraalVM, and others. While the core functionality is the same, each implementation may offer unique features and optimizations.