堆栈.txt

package ali.interview;

public class ListStack {
	class Node{
		private Object data;
		private Node next;
		
		public Node() {
			this.data = null;
			this.next = null;
		}
		
		public Node(Object data) {
			this.data = data;
			this.next = null;
		}
		
		public Object getData() {
			return data;
		}
		public void setData(Object data) {
			this.data = data;
		}
		public Node getNext() {
			return next;
		}
		public void setNext(Node next) {
			this.next = next;
		}			
	}
	
	private Node top;	
	
	public Node getTop() {
		return top;
	}

	public void setTop(Node top) {
		this.top = top;
	}

	public ListStack() {
		top = new Node();
	}
	
	public boolean isNull() {
		if(top.getNext() == null)
			return true;
		return false;
	}
	
	public void push(Node node) {
		if(this.isNull()) {
			top.setNext(node);
		}else {
			node.setNext(top.getNext());
			top.setNext(node);
		}		
	}
	
	public Object pop() {
		if (this.isNull()) {
			return null;
		}else {
			Node n = top.getNext();
			top.setNext(n.getNext());			
			return n.getData();
		}
	}
	
	public static void main(String[] args) {
		
		ListStack ls = new ListStack();
		System.out.println(ls.isNull());
		ls.push(ls.new Node(5));
		ls.push(ls.new Node('g'));
		ls.push(ls.new Node(7));
		
		System.out.println(ls.pop());
		System.out.println(ls.pop());
		System.out.println(ls.pop());
		System.out.println(ls.pop());
	}

}