自定义栈

栈，类似一个有底的箱子，当向箱子放东西时，先放进去的会被压在底部，而取出时，则后放进去的会被先取出来

//链表是以节点为单位的，对于单向链表，每个节点中包含一个值和指向下一个对象的引用
public class Node {
     Object value;
        Node next;

        public Node(Object value) {
            this.value = value;
        }

        public Object getValue() {
            return value;
        }

        public void setValue(Object value) {
            this.value = value;
        }

        public Node getNext() {
            return next;
        }

        public void setNext(Node next) {
            this.next = next;
        }
    
}


//自定义链表实现栈结构
public class MyStack {

    Node head = null;
    int size = 0;

    public int getSize() {
        return size;
    }

    //入栈
    public void push(Object value) {
        Node newNode = new Node(value);
        //如果头元素不存在
        if (head == null) {
            head = newNode;
        } else {
            //关联成串
            newNode.setNext(head);
            //改变指向
            head = newNode;
        }
        size++;

    }

    //出栈
    public Object pop() {
        Object value = head.getValue();
        head = head.getNext();
        size--;
        return value;
    }

    //查看栈顶元素
    public Object peek() {
        return head.getValue();
    }    
}

//测试
public class StackTest {

    public static void main(String[] args) {
        MyStack mystack=new MyStack();
        mystack.push(1);
        mystack.push(2);
        mystack.push(3);
        mystack.push(4);
        //pop会改变元素的size，导致执行两次就结束了
//        for (int i = 0; i < mystack.getSize(); i++) {
//            System.out.println(mystack.pop());
//        }
//        

        //结果最后放进去的4，别首先取了出来，结果为4 3 2 1


        while (mystack.getSize()>0) {
            System.out.println(mystack.pop());
        }
    }
}