Java 当用户选择除1或2之外的其他内容时，如何打印消息

我想要一个if语句，它不会让用户选择其他内容并打印错误消息

while (!done) {

        String str1 = JOptionPane.showInputDialog("1:Student, 2:Graduate");
        if (str1.equals("1")) {
        //code
        } else if (str1.equals("2")) {
           //code`enter code here`
        } else if (str1.isEmpty()) {
            System.err.println("You have to choose between 1 and 2");
        }
}

---

您需要与

if

和

else if

一起使用，如下所示：

String str1 = JOptionPane.showInputDialog("1:Student, 2:Graduate");
                if (str1.equals("1")) {
                  System.out.println("Your chose 1");
        }

                else if (str1.equals("2")) {
                    System.out.println("Your chose 2");
        }

                else if (str1.isEmpty()) {
                    System.err.println("You have to choose between 1 and 2, your input is empty !");
        }

                else {
                    System.err.println("You have to choose between 1 and 2");
                }
            }
        }