Question

基本上，我尝试进行测试并坚持关于垃圾收集器的问题：

以下代码段中有多少可用于System.gc（）的对象：

public class WorkGC {
    static class StaticNestedClass  {
        private String name;
        public StaticNestedClass(String name) {
        this.name = name;
        }
    }

    public static void main(String[] args) {
        StaticNestedClass n1 = new StaticNestedClass("n1");
        StaticNestedClass n2 = new StaticNestedClass("n2");
        Collection list = new ArrayList();
        list.add(n1);
        StaticNestedClass[] arr = new StaticNestedClass[2];
        arr[0] = n2;
        n2 = n1;
        clear(arr);
        n1 = null;
        n2 = null;
        System.gc();
       //the rest of the code
    }

    private static void clear(StaticNestedClass[] arr) {
        arr = null;
    }
}

我认为有两个对象可用：

1）arr - 在清除（arr）之后

2）n2 - 在n2 = null之后

我不确定arr - 是一个对象，可能是arr是一系列对象。另外，我不确定StaticNestedClass的实例，它是静态的并且位于PermGen中 - 而不是作为典型对象在Heap中。 GC是否在PermGen以及堆中工作？

Answer 1

我认为：`没有对象为GC做好准备。我认为这将是情景：

public static void main(String[] args) {
        StaticNestedClass n1 = new StaticNestedClass("n1"); //  1st object created 
        StaticNestedClass n2 = new StaticNestedClass("n2");  // 2nd object created 
        Collection list = new ArrayList(); // 3rd object
        list.add(n1); // n1 has a strong reference, so n1 is not ready for GC.
        StaticNestedClass[] arr = new StaticNestedClass[2];// 4th object created
        arr[0] = n2; //n2 has strong reference, so, even n2 is not ready.
        n2 = n1; // both n1 and n2 point to same object as that of n1. but arr[0] still references n2. 
        clear(arr); // you are passing references by value. SO, this has absolutely no effect on GC.
        n1 = null;// Object pointed to by n1 is still being referenced by n2
        n2 = null; //Object pointed to by n1 has a reference in the list.
        System.gc();
       //the rest of the code
    }


    private static void clear(StaticNestedClass[] arr) {
        arr = null;
    }

因此，基本上No Object已准备好用于GC。

System.gc（）的可用对象

1 个答案: