Question

您好我正在编写一个用户输入的简单用户名/密码，但是我的代码绕过所有if / if else语句并转到else语句。我不确定我的语法是否不正确或者使用if / else语句是否不正确。或者如果我只是编码错了。请帮忙！

import java.util.Scanner;

public class Passwords
{
    public static void main (String[] args)
    {
        Scanner input = new Scanner(System.in);
        String[] username = {"admin1", "admin2", "admin3", "admin4", "admin5"};
        String[] password = {"pass1", "pass2", "pass3", "pass4", "pass5"};
        System.out.println("Please enter in one of the following usernames : admin1, admin2, admin3, admin4, or admin5");
        String userinput = input.nextLine();
        System.out.println("Please enter in the password corresponding to your username: pass1, pass2, pass3, pass4, or pass5");
        String passinput = input.nextLine();
        if (userinput == username[0] && passinput == password[0])
        {
            System.out.println("Access granted!");
        }
        else if (userinput == username[1] && passinput == password[1])
        {
            System.out.println("Access granted!");
        }
        else if (userinput == username[2] && passinput == password[2])
        {
            System.out.println("Access granted!");
        }
        else if (userinput == username[3] && passinput == password[3])
        {
            System.out.println("Access granted!");
        }
        else if (userinput == username[4] && passinput == password[4])
        {
            System.out.println("Access granted!");
        }
            else 
            {
                System.out.println("Sorry the username or password you entered is incorrect. Please try again");
                System.out.println("Please enter in one of the following usernames : admin1, admin2, admin3, admin4, or admin5");
                String userinput1 = input.next();
                System.out.println("Please enter in the password corresponding to your username: pass1, pass2, pass3, pass4, or pass5");
                String passinput1 = input.next();
                if (userinput1 == username[0] && passinput1 == password[0])
                {
                    System.out.println("Access granted!");
                }
                else if (userinput1 == username[1] && passinput1 == password[1])
                {
                    System.out.println("Access granted!");
                }
                else if (userinput1 == username[2] && passinput1 == password[2])
                {
                    System.out.println("Access granted!");
                }
                else if (userinput1 == username[3] && passinput1 == password[3])
                {
                    System.out.println("Access granted!");
                }   
                else if (userinput1 == username[4] && passinput1 == password[4])
                {
                    System.out.println("Access granted!");
                }
                else 
                {
                    System.out.println("Sorry, your username/password does not match our database. Contact the administrator.");
                }
            }
        }
}

Answer 1

use，userinput.equals(username[0]) //这将比较字符串值

在java ==中将比较对象id＆＃39;如果它们是不同的对象，它将始终为false。

Answer 2

在Java中，正在使用字符串比较string1.equals(string2)。

Answer 3

使用String类的equals（）方法进行比较

userinput == username[0] to userinput.equals(username[0])


== tests for reference equality.

.equals() tests for value equality.

例如：

new String(userinput).equals(username[0]) // --> true 

new String(userinput) == username[0] // --> false 

new String(userinput) == new String(username[0]) // --> false

if / else语句中的JAVA Scanner字符串输入

3 个答案: