在while循环中的三个if-cases中的一个似乎不起作用,而另外两个呢？

Question

我正在尝试用Java编写一个小程序,让用户输入四个字符串(用户名,电子邮件,密码,密码).

该程序应该检查这些字符串是否满足while循环中的某些条件,这要求用户输入上述字符串,直到它们满足这些条件.

该程序编译,前两个if案例似乎工作正常.只有两个密码(password和passcheck)之间的比较似乎是错误的.即使我两次输入相同的字符串,它们也没有通过比较,我不知道为什么会这样.

import java.util.Scanner;

public class Registry {
    public static void main (String [] args){
        Scanner scanner = new Scanner(System.in);

        // Dialogue for the user to fill
        System.out.println("Please enter your username (at least 5 characters)");
        String username = scanner.nextLine();
        System.out.println("Please enter a valid emailadress (an @ is necessary for it to pass.)");
        String email = scanner.nextLine();
        System.out.println("Please enter two matching passwords, so we can make sure that you entered them correctly.");
        String password = scanner.nextLine();
        String passcheck = scanner.nextLine();
        boolean user = false;
        boolean mail = false;
        boolean pass = false;

        // Error messages within a loop in order to make the user enter valid arguments.
        while (user != true && mail != true && pass != true){
            if ((username == "" || username.length() < 5) || (username == " " || username.length() < 5)) {
                System.out.println("Username is empty or does not have enough characters! Please enter another.");
                username = scanner.nextLine();
            }
            else{
                user = true;
            }

            if (email.contains("@") == false){
                System.out.println("Invalid Mailadress. Please enter again.");
                email = scanner.nextLine();
            }

            else{
                mail = true;
            }

            if(password == passcheck){
                pass = true;
            }
            else if {

                System.out.println("Your passwords do not match. Please enter them correctly.");
                password = scanner.nextLine();
                passcheck = scanner.nextLine();
            }
        }

    }
}

Answer 1

if(password.equals(passcheck)){
        pass = true;
    }

与==您比较对象引用而不是值.

此外,你可以简化这个:

if ((username == "" || username.length() < 5) || (username == " " || username.length() < 5)) {

至

if (username.trim().length() < 5) {