栈和队列

public class StackToQueue<T> {

private Stack<T> stack1 = new Stack<T>();
private Stack<T> stack2 = new Stack<T>();

public void appendTail(T element){
    stack1.push(element);
}

public T deleteHead(){
    if(stack2.size() <= 0){
        while(!stack1.empty()){
            T element = stack1.pop();
            stack2.push(element);
        }
    }

    //说明stack1 也没元素了
    if(stack2.isEmpty()){
        throw new RuntimeException("队列为空");
    }

    T head = stack2.pop();
    return head;
}

public static void main(String[] args){
    StackToQueue<Integer> queue = new StackToQueue<Integer>();
    queue.appendTail(1);
    queue.appendTail(2);
    queue.appendTail(3);
    Integer a = queue.deleteHead();
    queue.appendTail(4);
    Integer b = queue.deleteHead();
    System.out.println(b);
}
}

public class StackToQueue<T> {

private Stack<T> stack1 = new Stack<T>();
private Stack<T> stack2 = new Stack<T>();

public void appendTail(T element){
    stack1.push(element);
}

public T deleteHead(){
    if(stack2.size() <= 0){
        while(!stack1.empty()){
            T element = stack1.pop();
            stack2.push(element);
        }
    }

    //说明stack1 也没元素了
    if(stack2.isEmpty()){
        throw new RuntimeException("队列为空");
    }

    T head = stack2.pop();
    return head;
}

public static void main(String[] args){
    StackToQueue<Integer> queue = new StackToQueue<Integer>();
    queue.appendTail(1);
    queue.appendTail(2);
    queue.appendTail(3);
    Integer a = queue.deleteHead();
    queue.appendTail(4);
    Integer b = queue.deleteHead();
    System.out.println(b);
}
}