How does the Java virtual machine manage memory?

JVM memory management ensures efficient use of application memory by dividing stack areas, including Java heap, method area, program counter, virtual machine stack and local method stack. Two garbage collection algorithms, mark-sweep and copy, are used to release objects that are no longer used and prevent memory leaks.

Java Virtual Machine (JVM) Memory Management

JVM’s memory management is crucial to ensure that the application is executing Have efficient and safe memory usage in the process.

JVM Memory Regions

The JVM divides the stack into several regions, each with a specific purpose.

• Java Heap: Used to store objects, which are created while the program is running. It is the largest pool of allocated objects in the application.
• Method area: Stores information about classes and interfaces loaded into the application.
• Program Counter: Tracks the bytecode instructions being executed by the current thread.
• Virtual machine stack: Storage local variables, parameters and return addresses when calling methods.
• Native method stack (unused): Stores information when calling native methods.

Garbage Collection

The JVM uses a garbage collector to automatically release objects that are no longer used, thereby preventing memory leaks. There are two main garbage collection algorithms:

• Mark-Purge: Mark objects that are no longer used and then clear the memory occupied by these objects.
• Copy: Copy the active (still used) object to a new memory area, and then release the memory in the old area.

Practical case

The following code demonstrates how the JVM allocates and releases objects in the heap:

public class MemoryManagement {

    public static void main(String[] args) {
        // 创建一个新对象
        Object object = new Object();

        // 将对象引用设置为 null 以释放内存
        object = null;

        // 运行垃圾回收器
        System.gc();
    }
}

RunningSystem After .gc(), the JVM will detect that the object is no longer referenced by any reference and release the memory occupied by the object to the heap.

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