package com.hb.ds.stack;

class Node {

public Node previous;
public T value;

public Node(T value, Node previous){
  this.previous = previous;
  this.value = value;
}

public Node(T value){
  this.previous = null;
  this.value = value;
}
}

class Stack {

private int count = 0;

public Node first = null;

/**
* 进栈
* @param o
*/
public void push(T o) {
  first = new Node(o, first); //让Node的next指针指向first这个Node ,然后在让first指向这个新建立的Node (这句很关键，必须理解)
          //这样写好理解一些：Node temp = new Node(o,first);
          //               first = temp;
  count++;
  System.out.println("数据入栈成功 " + o);
}

/**
* 出栈
* @return
*/
public T pop() {
  if (first == null) {
   throw new NullPointerException();
  } else {
   T temp = first.value;
   System.out.println("数据正在出栈成功"+first.value);
   first = first.previous; //关键的一句
   count--;

   System.out.println("数据出栈成功");
   return temp;
  }
}

public void clear(){
  while(count!=0){
   pop();
  }
}
}

public class StackTest {

public static void main(String[] args){
  Stack s = new Stack();
  s.push("23");
  s.push("24");
  s.push("25");
  s.push("26");

  s.pop();

  s.clear();
}
}

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JAVA实现stack2

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