How does the garbage collector work in Java memory management?

Java memory management uses the garbage collector to reclaim objects that are no longer referenced and release memory. Common garbage collectors include: Serial GC: single-threaded, suitable for small programs. Parallel GC: multi-threaded, suitable for large programs. Concurrent Mark Sweep GC: runs concurrently. G1 GC: Predictable pause times, efficient memory utilization. Optimizing garbage collection performance can be achieved by reducing object lifetimes, avoiding unnecessary object creation, using weak references, and adjusting garbage collector settings.

Garbage Collector in Java Memory Management: Principles and Practical Cases

Introduction
The garbage collector is an important memory management mechanism in Java, responsible for recycling objects that are no longer referenced and releasing the memory they occupy. Java provides different garbage collectors, each with different algorithms and performance characteristics.

Garbage collection algorithm

• Mark-clear algorithm: Mark all reachable objects, and then clear unmarked objects.
• Mark-organize algorithm: Similar to the mark-sweep algorithm, but will organize the remaining objects into contiguous spaces in memory.
• Copy algorithm: Copy the reachable object to a new memory area, and then release the old memory area.

Common garbage collectors

Java provides the following common garbage collectors:

• Serial GC : Single-threaded garbage collector, suitable for small programs.
• Parallel GC: Multi-threaded garbage collector, suitable for large programs.
• Concurrent Mark Sweep GC: A garbage collector that runs concurrently with the application.
• G1 GC: The latest garbage collector with predictable pause times and efficient memory utilization.

Practical case

In the following code example, we add an object to an ArrayList and then set it to null to make the object inaccessible:

import java.util.ArrayList;

public class GCExample {
    public static void main(String[] args) {
        ArrayList<Integer> list = new ArrayList<>();

        for (int i = 0; i < 100000; i++) {
            list.add(i);
        }

        list = null;  // 使 ArrayList 不可访问
    }
}

When this code runs, the objects in the ArrayList will no longer be referenced and the garbage collector will reclaim them to free up memory.

Optimize garbage collection performance

In order to optimize garbage collection performance, you can perform the following operations:

• Reduce the life cycle of objects.
• Avoid creating unnecessary objects.
• Use weak or soft references to indicate whether an object is still needed.
• Adjust garbage collector settings to meet the needs of your specific application.

Conclusion

By understanding the characteristics of garbage collection algorithms and common garbage collectors, you can optimize the memory management of Java applications and improve application performance and memory efficiency.

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