Memory management and garbage collection techniques in Java

As a high-level programming language, the quality of Java's memory management and garbage collection technology directly affects the performance and stability of the program. This article will introduce memory structures in Java and how to perform memory management and garbage collection.

1. Java’s memory structure

Java virtual machine memory is divided into three main parts:

1. Heap: All objects allocate memory space in the heap . The heap is the largest piece of memory managed by the Java virtual machine, and its size changes dynamically as the application runs.
2. Stack: Each thread has its own stack, which stores references to basic types and objects. The size of the stack is determined at compile time.
3. Method area: stores class information, static variables, constants, compiled code, etc. The method area also changes dynamically as the application runs.

2. Memory management in Java

The Java language has its own memory management function, and programmers can automatically manage memory through Java's built-in garbage collector. The garbage collector can track the usage of objects. When an object becomes unreachable, the garbage collector will automatically reclaim its memory space.

The following are several common memory management technologies:

1. Memory pool

The memory pool is a kind of memory that is allocated when the program starts. , which is returned to the operating system at the end of the program. The benefit of the memory pool is to reduce frequent memory allocation and destruction operations and improve program performance.

The memory pool in Java is different from the memory pool in C. The memory of Java objects is allocated in the heap, so the memory pool manages the memory in the heap.

2. Weak reference

Weak reference is a reference that does not increase the life cycle of the object. Under normal circumstances, after an object is referenced by a weak reference, as long as there is no strong reference pointing to it, the garbage collector will reclaim the memory space of the object.

3. Soft reference

Soft reference is a reference that can increase the life of an object. When memory is low, the garbage collector reclaims objects referenced by soft references. Compared with weak references, soft reference objects last longer.

3. Garbage collection technology in Java

The garbage collector in Java implements automatic memory recycling, and programmers do not need to manually recycle objects that are no longer used. Here are several common garbage collection techniques:

1. Mark sweep

Mark sweep is one of the original garbage collection algorithms. The algorithm first traverses the entire heap space, marking all objects that are still referenced, and then clearing all unmarked objects. However, the mark and sweep algorithm has the problem of memory fragmentation, resulting in smaller available memory space.

2. Copy algorithm

The copy algorithm is designed to solve the memory fragmentation problem of the mark and clear algorithm. The principle of the copy algorithm is to divide the heap memory into two areas of equal size. When one area runs out of space, the surviving objects are moved to the other area. The advantage of this is that after each memory recycling, the available memory space is continuous.

3. Mark compression algorithm

The mark compression algorithm is an improved version of the mark removal algorithm. The algorithm first marks all objects that are still referenced, and then compresses the surviving objects to one side to form a continuous memory space. The advantage of this is that it solves the memory fragmentation problem of the mark and clear algorithm.

4. Conclusion

In Java development, effective memory management and garbage collection technology are very important. Programmers should be familiar with Java's memory structure and garbage collection technology, and adopt appropriate memory management methods to optimize the performance and stability of applications.

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