栈的链式存储结构

package MyJava2;

public class LinkStack {
    private class Node{
        String data;
        Node next;
        public Node(){}
        public Node(String data,Node next){
            this.data=data;
            this.next=next;
        }
    }
    private Node top;
    private int size=0;

    public LinkStack(){//建立空栈
        top=null;
        size=0;
    }
    public LinkStack(String data){//指定元素建栈
        top=new Node(data,null);
        size++;
    }

    public int len(){
        return size;
    }

    public void push(String data){//进栈
        top=new Node(data,top);
        size++;
    }
    public String pop(){//出栈
        Node old=top;
        top=top.next;
        old.next=null;
        size--;
        return old.data;
    }
    public String peek(){//访问栈顶元素但不删除
        return top.data;
    }

    public boolean empty(){//判断是否是空栈
        return size==0;
    }
    public void clear(){//清空链栈
        top=null;
        size=0;
    }

    public String toString(){
        StringBuffer sb=new StringBuffer();
        Node current=top;
        for(;current!=null;current=current.next){
            sb.append(current.data+",");
        }
        return sb.toString();
    }
    public static void main(String[] args){
        LinkStack stack=new LinkStack("A");
        stack.push("B");
        stack.push("C");
        System.out.println(stack.toString());
        System.out.println(stack.pop());
        System.out.println(stack.peek());
        System.out.println(stack.size);
        stack.clear();
        System.out.println(stack.empty());
    }

}

采用单链表保存栈中的元素，只使用一个top记录栈顶元素。