未调用java finalize（）

Question

为什么这里没有调用finalize()。代码编译并运行成功，但没有任何输出

package temp;

public class Temp {

    int i;

    Temp(int j) {
        i = j;
    }

    public void finalize() {
        if (i == 10) {
            System.out.println("Finalize called.");
        }
    }

    public static void main(String[] args) {
        Temp obj = new Temp(10);
        System.gc();
    }

}

Answer 1

碰巧我在读Effective Java

第7项：避免使用终结器

Finalizers are unpredictable, often dangerous, and generally unnecessary. -Effective Java (page 50)

另一个来自pdf

Don’t be seduced by the methods System.gc and System.runFinalization . They may increase the odds of finalizers ge tting executed, but they don’t guaran- tee it. The only methods that claim to guarantee finalization are System.runFi- nalizersOnExit and its evil twin, Runtime.runFinalizersOnExit . These methods are fatally flawed and have been deprecated [ThreadStop].

基于此使用系统。gc只会增加终结器被执行的几率，重要的是，使用它并不能保证它将运行垃圾收集，它只是向jvm建议

另一个

Not only does the language specification provide no guarantee that finalizers will get executed promptly; it provides no guarantee that they’ll get executed at CHAPTER 2 CREATING AND DESTROYING OBJECTS 28 all. It is entirely possible, even likely, that a program terminates without executing finalizers on some objects that are no longer reachable

Answer 2

添加obj = null;使引用为null，然后将调用finalize方法。Thsi再次不是一种保证行为，对我来说，有1-2次我能在5次中说出它

 public static void main(String[] args) {
        Temp obj = new Temp(10);
        obj  = null;
        System.gc();
    }

输出

hi10
Finalize called.

Answer 3

创建对象时，会调用构造函数，但不会调用finalize（）方法，因此需要引用实例obj中的函数，此处为系统。gc（）；没有任何区别或调用了方法finalize（）

Answer 4

您对System.gc();的调用没有任何区别，因为您的Temp实例有一个引用（obj），所以它不符合垃圾收集的条件

即使它符合垃圾收集的条件，调用System.gc();也不一定会立即收集所有没有引用的对象