Learn from the JVM core framework in the Java class library
Learn from the JVM core framework in the Java class library
Java is a widely used programming language, and JVM (Java virtual machine) is the operating environment performed by the Java application.The JVM core framework is the basic component of JVM. Mastering its working principle is essential to understand the internal mechanism of the Java class library.This article will explore the relevant knowledge of the JVM core framework and provide some Java code examples.
1. JVM Basic Overview
JVM is a virtual computer that is used to explain and execute the Java bytecode.It is mainly composed of the following core components:
-ClassLoader: Responsible for loading the byte code to the memory and converting it into an executable Java class.
-Execution Engine: Execute the bytecode instructions of the class loaded.
-Memory Management Subsystem: Responsible for the distribution and recycling of memory, including heap, stack and method area.
-Natic method interface (Native Method Interface): Used to call local code written in other languages in Java virtual machines.
-The data area (Runtime Data Area): Including method areas, stacks, stacks, programmeters, and local method stacks.
2. Class loader
The class loader is one of the important components of JVM, which is responsible for loading the Java file to the memory.JVM provides three types of loaders: bootstrap class loader, Extension Class loader, and Application Class loader.The following is a simple example:
public class ClassLoaderExample {
public static void main(String[] args) {
ClassLoader classLoader = ClassLoaderExample.class.getClassLoader();
System.out.println("ClassLoader: " + classLoader);
System.out.println("Parent ClassLoader: " + classLoader.getParent());
}
}
Output results:
ClassLoader: jdk.internal.loader.ClassLoaders$AppClassLoader@2f7c7263
Parent ClassLoader: jdk.internal.loader.ClassLoaders$PlatformClassLoader@6d06d69c
3. Execute engine
The execution engine is one of the core components of JVM, which is responsible for explaining and executing bytecode instructions in the Java class.There are two common execution engines: interpreter (interpreter) and Just-in-Time Compiler (JIT).The interpreter explains the byte code instruction one by one, and the execution speed is relatively slow; the instant compiler will compile the byte code to the cost of the machine code to improve the execution speed.The following is a simple example:
public class ExecutionEngineExample {
public static void main(String[] args) {
int x = 5;
int y = 10;
int sum = x + y;
System.out.println("Sum: " + sum);
}
}
4. Memory Management subsystem
The memory management subsystem is responsible for allocating and recycling memory resources and managed the Java object.It mainly includes Heap, Stack, and Method Area.It is used for storage object instances, stacks are used to store method calls and local variables, and the method region is used to store structural information.The following is a simple example:
public class MemoryManagementExample {
public static void main(String[] args) {
int[] array = new int[5];
array[0] = 1;
array[1] = 2;
System.out.println("Array Length: " + array.length);
System.out.println("Array Element at Index 0: " + array[0]);
System.out.println("Array Element at Index 1: " + array[1]);
}
}
5. Local method interface
Local method interface allows Java virtual machines and local code to interact.When Java calls the local code, it will be implemented through the local method interface.The following is a simple example:
public class NativeMethodInterfaceExample {
static {
System.loadLibrary("nativeLibrary");
}
private native void nativeMethod();
public static void main(String[] args) {
NativeMethodInterfaceExample example = new NativeMethodInterfaceExample();
example.nativeMethod();
}
}
6. Data area during runtime
Data areas include method areas, heaps, stacks, programmeters, and local method stacks.These areas correspond to different functions during the JVM operation.The method area is used to store the structural information of the class, stack it for the storage object instance, the stack is used to store method calls and local variables, the programmeter is used to record the position of execution, and the local method stack is used to store the execution information of the local code.
In summary, the knowledge of mastering the JVM core framework is essential for the development of Java.By understanding components such as class loaders, execution engines, memory management subsystems, local method interfaces, and data areas such as data areas, developers can better understand the internal mechanism of the Java class library, and write more efficient and reliable Java applicationsEssence
It is hoped that this article can help readers understand the JVM core framework in the Java class library.
