链表实现栈、队列

package repeat_job1;

public class Stack_Queue {
private Object data;
private Stack_Queue next,First,obj2=null,temp=this;
private int flag=0;
public Stack_Queue(){}
public Stack_Queue(Object data){
this.data=data;
}
public void push(Object data)
{
Stack_Queue obj1;
obj1=new Stack_Queue(data);
obj1.next=this.next;
this.next=obj1;
}
public boolean stack_IsEmpty()
{
temp=temp.next;
return temp==null;

}
public Object pop()
{
return temp.data;
}
public void in_Queue(Object data)
{
Stack_Queue obj3;
obj3=new Stack_Queue(data);
if(obj2==null)//obj2.next会出现空指针！
{
obj2=obj3;
First=obj2;
obj2.next=this;
}
obj3.next=this;
obj2.next=obj3;
obj2=obj3;//obj2要紧跟obj3；

}
public boolean queue_IsEmpty()
{
if(flag==1)
{
First=First.next;
return First.next==null;
}
else
{
return First.next==null;
}

}
public Object out_Queue()
{
flag=1;
return First.data;
}

}

import repeat_job1.Stack_Queue;
public class Stack_Queue_Test {
public static void main(String[] args)
{
Stack_Queue obj1=new Stack_Queue();
obj1.push("hello");
obj1.push("world");
obj1.push("张三");
obj1.push(23333);
System.out.println("出栈：");
while(!obj1.stack_IsEmpty())
{
System.out.print(obj1.pop()+" ");
}
System.out.println();
Stack_Queue obj2=new Stack_Queue();
obj2.in_Queue("hello");
obj2.in_Queue("world");
obj2.in_Queue("张三");
obj2.in_Queue(23333);
System.out.println("出队：");
while(!obj2.queue_IsEmpty())
{
System.out.print(obj2.out_Queue()+" ");
}
}

}