深入聊聊Java内存泄露问题

import java. io.IOException;
public class GarbageTest {

    public static void main(String[] args) throws IOException {
        try {
            // TODO Auto-generated method stub
            gcTest();
        } catch (IOException e) {
            e.printStackTrace();
        }

        System.out.println("has exited gcTest!");
        System.in.read();
        System.in.read();
        System.out.println("out begin gc!");
        for (int i = 0; i < 100; i++) {
            System.gc();
            System.in.read();
            System.in.read();
        }
    }

    private static void gcTest() throws IOException {
        System.in.read();
        System.in.read();
        Person p1 = new Person();
        System.in.read();
        System.in.read();
        Person p2 = new Person();
        p1.setMate(p2);
        p2.setMate(p1);
        System.out.println("before exit gctest!");
        System.in.read();
        System.in.read();
        System.gc();
        System.out.println("exit gctest!");
    }

    private static class Person {
        byte[] data = new byte[20000000];
        Person mate = null;

        public void setMate(Person other) {
            mate = other;
        }
    }

}

public class Stack {
    private Object[] elements = new Object[10];
    private int size = 0;

    public void push(Object e) {
        ensureCapacity();
        elements[size++] = e;
    }

    public Object pop() {
        if (size == 0) throw new EmptyStackException();
        return elements[--size];
    }

    private void ensureCapacity() {
        if (elements.length == size) {
            Object[] oldElements = elements;
            elements = new Object[2 * elements.length + 1];
            System.arraycopy(oldElements, 0, elements, 0, size);
        }
    }
}

class Bad {
    public static Stack s = new Stack();
    static {
        s.push(new Object());

        s.pop(); //这里有一个对象发生内存泄露

        s.push(new Object());//上面的对象可以被回收了，等于是自愈了
    }
}

public class Stack{  
      private Object[] element=new Object[10];  
      private int size=0;  
        
      public void push(Object ele){  
             ensureCapacity();  
             element[size++]=ele;  
      }  
  
      public Object pop(){  
             if(size==0) throw new EmptyStackException();  
             return element[--size]; //短暂造成内存泄露  
      }  
  
      private void ensureCapacity(){  
             if(element.length==size){  
                     Object[] oldElement=element;  
                     element=new Object[size*2+1];  
                     System.arraycopy(oldElement,0,element,0,size);  
             }  
      }  
}  

public Object pop(){  
       if(element.length==size) throws EmptyStackException();  
       Object o=element[--size];  
       elements[size]=null;  //使得GC有机会回收这个对象  
       return o;  
}