Java underlying technology practice: how to implement memory allocation and garbage collection

Java underlying technology practice: how to implement memory allocation and garbage collection, specific code examples are required

Introduction:
In Java programming, memory allocation and garbage collection is a very important topic. Memory allocation refers to how to effectively allocate memory to objects when the program is running, while garbage collection refers to how to reclaim the memory when the objects are no longer used. This article will introduce the underlying memory allocation and garbage collection mechanisms in Java and provide some specific code examples.

1. Memory allocation
In Java, memory allocation is mainly achieved through the automatic memory management of the garbage collector. In the Java Virtual Machine (JVM), there is a heap (Heap) used to store object instances. When a program creates a new object, the JVM allocates memory space for it on the heap. However, in order to improve the efficiency of memory allocation, the JVM uses an algorithm called "Bump the Pointer".

The basic idea of ​​the pointer collision algorithm is that the heap is a continuous memory space, and the JVM records the starting position of the current free memory through a pointer. When you need to allocate memory for a new object, you just increment the pointer to the beginning of the next available memory and mark that memory as allocated. If there is insufficient memory, the JVM will trigger the garbage collection mechanism to recycle memory.

Code example:
The following is a simple Java code example that demonstrates the process of memory allocation:

public class MemoryAllocationExample {
    public static void main(String[] args) {
        // 创建一个新对象，内存将被分配给该对象
        MyClass obj1 = new MyClass();
        
        // 创建另一个新对象，内存将被分配给该对象
        MyClass obj2 = new MyClass();
    }
}

class MyClass {
    // 在此省略类的成员变量和方法...
}

In the above code, two new ## are created respectively #MyClassObjectsobj1 and obj2. When each object is created, the JVM allocates memory space for it according to the pointer collision algorithm.

2. Garbage Collection

When an object is no longer referenced by the program, it can be considered that the object has become garbage. In order to reclaim the memory occupied by these garbage objects, the JVM has a garbage collector (Garbage Collector), which is responsible for scanning the objects in the program, finding those objects that are no longer referenced, and releasing the memory space occupied by them.

The garbage collector in Java usually uses a generational collection algorithm. This algorithm assumes that the life cycle of an object can be divided into several stages, such as the young generation and the old generation. Newly created objects will first be allocated to the young generation, and objects that survive after a certain number of garbage collections will be transferred to the old generation.

Code example:

The following is a simple Java code example that demonstrates the process of garbage collection:

public class GarbageCollectionExample {
    public static void main(String[] args) {
        // 创建一个新的MyClass对象，并将其赋值给变量obj
        MyClass obj = new MyClass();
        
        // 将变量obj置为null，不再引用对象
        obj = null;
        
        // 进行垃圾回收
        System.gc();
    }
}

class MyClass {
    // 在此省略类的成员变量和方法...
    
    @Override
    protected void finalize() throws Throwable {
        // 在垃圾回收前执行清理操作
        // 如释放占用的资源等
    }
}

In the above code, first create a new

MyClass object and assign it to variable obj. Then set obj to null, indicating that the object is no longer referenced. Finally, call the System.gc() method to trigger garbage collection.

Note that the

finalize() method is a special method executed before garbage collection. In this method, you can write cleanup code, such as releasing occupied resources. However, it is not recommended to rely too much on the finalize() method because its execution timing is uncertain.

Conclusion:

This article introduces the memory allocation and garbage collection mechanism in the practice of Java's underlying technology, and provides specific code examples. By learning this knowledge, we can better understand the basic principles of Java memory management and be able to write more efficient and reliable Java programs. At the same time, in actual programming, we should also develop good coding habits to avoid memory leaks and resource waste.

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