剑指offer 用两个栈实现队列

import java.util.Stack;

/**
* Created by zj on 2017/3/11 0011.
*/
public class Queue<T> {
private Stack<T> stack1 = new Stack<T>();
private Stack<T> stack2 = new Stack<T>();
public void appendTail(T t){
stack1.push(t);
}
public T deleteHead() throws Exception{
if(stack2.isEmpty()){
while(!stack1.isEmpty()){
stack2.push(stack1.pop());
}
}
if(stack2.isEmpty()){
throw new Exception("队列为空，不能删除");
}
return stack2.pop();
}

}