栈和队列

import java.util.Stack;
public class  {
   private Stack<Integer> stackPush;
    private Stack<Integer> stackPop;
 public TwoStackQueue() {
       stackPush = new Stack<Integer>();
        stackPop = new Stack<Integer>();
 }
   
   * 添加队尾元素
   * @param data 添加的数据
    */
  public void add(int data) {
       stackPush.push(data);
   }
   
   * 删除队首的元素
  * @return 为空则返回null
    */
  public int poll() {
       if (stackPop.empty() && stackPush.empty()) { //如果两个栈都为空，则删除失败
           throw new RuntimeException("Queue is empty!");
        } else if (stackPop.empty()) { //如果栈2为空，则将栈1的内容全部弹出后压入
          stackPop.push(stackPush.pop());
     }
       return stackPop.pop();
 }
   
   * 访问队首元素,与上面的poll()方法相同，返回时不删除而已
   * @return
  */
  public int peek(){
        if (stackPop.empty() && stackPush.empty()) { //如果两个栈都为空，则删除失败
           throw new RuntimeException("Queue is empty!");
        } else if (stackPop.empty()) { //如果栈2为空，则将栈1的内容全部弹出后压入，弹出栈顶
         stackPop.push(stackPush.pop());
     }
       return stackPop.peek();
    }
}