2.栈:后进先出(LIFO)
package test.my.chap0302; import java.util.Stack; public class QueueWithTwoStack<E> { private Stack<E> stack1 = new Stack<E>(); private Stack<E> stack2 = new Stack<E>(); public void appendTail(E e){ stack1.push(e); } public EdeleteEle() throws Exception{ if(stack2.size()<=0){ while(!stack1.isEmpty()){ stack2.push(stack1.pop()); } } if(stack2.size()==0){ throw new Exception("Queue is empty!"); } return stack2.pop(); } }