如果陈述，否则我的输入将不被接受

Question

我正在生成一个从1到100的随机数，并将其显示给用户，然后我将有20次机会猜测该随机数。响应应该是“是”或“否”，但是现在当我运行该程序时，它只是从用户那里获取输入并结束执行，因此不会访问if else if循环

代码

public static void main(String args[])
{
    Random rand = new Random();
    int rand_int1 = rand.nextInt(100);
    System.out.println("Random value is = " + rand_int1);

    int n = 20;

    Scanner userinput = new Scanner(System.in);

    System.out.println("is your number is form 0 to 50 ?");
    String ans1 = userinput.nextLine();
    System.out.println("ans : " + ans1);

    if (ans1 == "yes") {
        System.out.println("number is more then 50");
    }
    else if (ans1 == "no") {
        System.out.println("number is less then 50");
    }
}

示例输出

Random value : 23

is your number is more then or equal to 50?
ans : No

稍后，我将添加更多代码，这也将出现在输出中：

is your number is less then or equal to 25?
ans : Yes