Java beginners, unfamiliar words (1), new java beginners encounter words

Java beginners, unfamiliar words (1), new java beginners encounter words

Bytecode file: it does not contain hardware information and is completely unrelated to the hardware platform. Therefore, it cannot be run directly by the operating system.

Java application execution process: Code loading, code validation, and code execution.

Java Virtual Machine (JVM): Virtual software platform. To enable the compilation of bytecode for better interpretation and execution, it is usually divided into six functional modules: JVM interpreter, command system, register, stack, storage area and fragment zone.

JVM Interpreter: converts bytecode into machine commands executed by the CPU;

Command System: similar to hardware computers;

Registers: four commonly used 32-bit registers: pc (program counter), optop (top pointer of the operand stack), and frame (current execution environment pointer), vars (execute the pointer of the first local variable );

STACK: the JVM stack is the place and control center for storing data and information during command execution. It provides the information required for calculation by the JVM interpreter;

Storage Area: The JVM storage area stores compiled bytecode information and provides raw materials for processing;

Fragments are charged: The specific instances of the used Java class are recycled from the memory to automatically release the memory.

The use of JVM enables Java to implement "one compilation and run everywhere", which is the core of the entire operating system.

JDK: it is a free Java development tool provided by Sun. It has three members: J2EE, J2SE, and j22;

J2EE: used on the Scalable enterprise-level application Java 2 platform;

J2SE: used on the Java standard platform of workstations and PCs;

J2SE: used on an embedded consumer electronics platform.

For example, JDK has different versions for Windows, for Linux, for Solaris, and MacOS. (JDK is backward compatible)