StackLink

public class StackLink {
    public static void main(String[] args){
        StackL<Integer> stack= new StackL<>();
        System.out.println(stack.isempty());
        stack.push(9);
        stack.push(5);
        stack.push(8);
        System.out.println(stack.peek());
        System.out.println(stack.length());
        System.out.println(stack.pop());
    }
}
class StackL<T>{

    //节点
    private class Node{
        T e;
        Node next;
        public Node(){}
        public Node(T e,Node next){
            this.e = e;
            this.next = next;
        }
    }

    private Node top = null; //栈顶元素
    private int size; //当前栈的大小


    //入栈
    public boolean push(T e){
        top = new Node(e,top);
        size++;
        return true;
    }

    //判断是否为空栈
    public boolean isempty(){
        return size == 0;
    }

    //查看元素但不删除
    public T peek(){
        if(isempty()){
            throw new RuntimeException("空栈异常！");
        }else{
            return top.e;
        }
    }

    //出栈
    public T pop(){
        if(isempty()){
            throw new RuntimeException("空栈异常！");
        }else{
            Node value = top;
            top = top.next;
            value.next=null;
            size--;
            return value.e;
        }
    }

    //当前栈的大小
    public int length(){
        return size;
    }

}