“终结者监护人”如何？在java中工作？ [英] How does a "finalizer guardian" work in java?

问题描述

finalizer guardian[Effective Java，page 30]如何工作？

你用过它们吗？它解决了任何特定的问题吗？

解决方案

它解决了忘记调用 finalize 超类的方法。这种模式通过附加一个额外的实例并重写 finalize 给你的超类。这样，如果超类超出范围，则附加实例也将超出范围，这将触发 finalize 的执行，然后依次调用封闭类的 finalize 。

下面是一个简短的代码片段， p>

  public class Parent {
 
 public static void main（final String [] args）throws Exception {
 doIt（）; 
 System.gc（）; 
 Thread.sleep（5000）; // 5秒睡眠
} 
 
 @SuppressWarnings（unused）
 private final object object guardian = new Object（）{
 @Override protected void finalize（） {
 doFinalize（）; 
} 
}; 
 
 private void doFinalize（）{
 System.out.println（Final class of Parent）; 
 
 
 public static void doIt（）{
 Child c = new Child（）; 
 System.out.println（c）; 
} 
 
} 
 
 class Child extends Parent {
 
 //注意，Child类不会调用super.finalize（），但是
 //父类持有的资源仍然会被清除，这要归功于监护人模式
 @Override protected void finalize（）{
 System.out.println（Finalize of class儿童）; 
} 
 
} 
  

How does a "finalizer guardian" [Effective Java , page 30] work ?

Have you used them? Did it solve any specific problem ?

解决方案

It solves the problem of the sub-class forgetting to call the finalize method of the super-class. This pattern works by attaching an extra instance with overridden finalize to your super-class. This way, if the super-class goes out of scope, the attached instance would also go out of scope, which would trigger the execution of its finalize, which would in turn call the finalize of the enclosing class.

Here is a short snippet that showcases the guardian pattern in action:

public class Parent {

    public static void main(final String[] args) throws Exception {
        doIt();
        System.gc();
        Thread.sleep(5000); //  5 sec sleep
    }

    @SuppressWarnings("unused")
    private final Object guardian = new Object() {
        @Override protected void finalize() {
            doFinalize();
        }
    };

    private void doFinalize() {
        System.out.println("Finalize of class Parent");
    }

    public static void doIt() {
        Child c = new Child();
        System.out.println(c);
    }

}

class Child extends Parent {

    // Note, Child class does not call super.finalize() but the resources held by the
    // parent class will still get cleaned up, thanks to the guardian pattern
    @Override protected void finalize() {
        System.out.println("Finalize of class Child");
    }

}

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