遞歸函數一：將棧stack的棧底元素返回并移除

public static int getAndRemoveLastElement(Stack<Integer> stack){
    int result =stack.pop();
    if(stack.isEmpty()){
        return result;
    }
    else{
        int last=getAndRemoveLastElement(stack);
        stack.push(result);
        return last;
    }
}

遞歸函數二：逆序一個棧

public static void reverse(Stack<Integer> stack){
    if(stack.isEmpty()){
        return;
    }
    int i=getAndRemoveLastElement(stack);
    reverse(stack);
    stack.push(i);
}