How does Java anonymous inner class solve memory leak problem?

Anonymous inner classes can cause memory leaks. The problem is that they hold a reference to the outer class, thus preventing the outer class from being garbage collected. Solutions include: 1. Use weak references. When the external class is no longer held by a strong reference, the garbage collector will immediately recycle the weak reference object; 2. Use soft references. The garbage collector will recycle the weak reference object when it needs memory during garbage collection. Only then the soft reference object is recycled. In practice, such as in Android applications, the memory leak problem caused by anonymous inner classes can be solved by using weak references, so that the anonymous inner class can be recycled when the listener is not needed.

Java Anonymous Inner Classes: How to Solve Memory Leak

Introduction

Anonymous Inner classes are unnamed inner classes written directly in the class or method that creates them. While anonymous inner classes can provide code simplicity, they can lead to memory leaks if not managed properly.

Generation of memory leaks

A memory leak occurs when an anonymous inner class holds a reference to its outer class. The outer class prevents garbage collection and the inner class will remain in memory even if it is no longer needed.

Solution

You can solve the memory leak problem in anonymous inner classes by using weak reference or soft reference . These references allow the garbage collector to reclaim the object when necessary, while still allowing access to the object if it has not already been reclaimed.

Use weak references

Weak references are the weakest reference types. When an object is no longer held by any strong reference, the garbage collector immediately reclaims the object holding a weak reference.

public class Example {

    private static class InnerClass {
        // ...
    }

    public static void main(String[] args) {
        // 创建外部类对象
        Example example = new Example();

        // 创建持有外部类引用的匿名内部类
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                // ...
            }
        };

        // 将匿名内部类弱引用
        WeakReference<Runnable> weakRunnable = new WeakReference<>(runnable);

        // ...

        // 显式取消强引用
        runnable = null;

        // 垃圾回收器将回收匿名内部类，因为只有弱引用持有其引用
    }
}

Use soft references

Soft references are stronger than weak references. The garbage collector only reclaims objects holding soft references when it needs memory while performing garbage collection.

public class Example {

    private static class InnerClass {
        // ...
    }

    public static void main(String[] args) {
        // 创建外部类对象
        Example example = new Example();

        // 创建持有外部类引用的匿名内部类
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                // ...
            }
        };

        // 将匿名内部类软引用
        SoftReference<Runnable> softRunnable = new SoftReference<>(runnable);

        // ...

        // 显式取消强引用
        runnable = null;

        // 垃圾回收器可能会在需要内存时回收匿名内部类，但只有当内存不足时才会回收
    }
}

Practical Case

The following is a practical case to solve the memory leak caused by anonymous inner classes in Android applications:

public class MyActivity extends Activity {

    private Button button;
    private View.OnClickListener listener;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_my);

        button = findViewById(R.id.button);

        // 使用弱引用解决内存泄漏
        listener = new WeakReference<>(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                // ...
            }
        }).get();

        button.setOnClickListener(listener);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();

        // 在 Activity 销毁时取消强引用
        listener = null;
    }
}

By using weak references , which prevents memory leaks by ensuring that anonymous inner classes are garbage collected when the listener is not needed.

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