java - SCJP测试题

Question

SCJP 测试题:

 class A{
      A aob;
      public static void main(String args[]){
           A a=new A();
           A b=new A();
           A c=new A();
           a.aob=b;
           b.aob=a;
           c.aob=a.aob;
           A d=new A().aob=new A();
           c=b;
           c.aob=null;
           System.gc();
      } 
  }

问题:c.aob=null执行后，有多少对象符合垃圾回收条件。

我认为是 1，但正确答案是 2。有什么问题吗？

Answer 1

我通过谷歌搜索找到了this thread .

The first object is the one referenced originally by c.

A a= new A();
A b= new A();
A c= new A();
a.aob=b;
b.aob=a;
c.aob=a.aob;
A d= new A().aob=new A();
c=b; //(1)

It becomes eligible at (1).

The other object eligible for GC is at statement

A d=new A().aob=new A();

Here the object created in the text in bold will be eligible for GC. The object in italicized text will be assigned to d.