Java 变量在案例结束时消失

我有一个问题，因为我不知道如何保存变量。变量newname和newpassword deafult为零。但在案例1中，它们被更改为给定值，但在案例1之后，变量返回到基本值0。我无法登录（在案例2中），因为登录名和密码始终为0。如何在案例1中全局设置此变量

    String newname = null;
    String newpassword = null;


    System.out.println("Hello!");
    System.out.println();
    System.out.println("     ****************************************");
    System.out.println("     *                 MENU                 *");
    System.out.println("     ****************************************");
    System.out.println("     1. Create new account");
    System.out.println("     2. Log in");
    System.out.println("     3. Help");
    System.out.println("     0. End");
    Scanner opcje = new Scanner(System.in);
    int choose = opcje.nextInt();

    switch (choose) {

        case 1:

            System.out.println("You choose create new acount\n Enter the login");
            Scanner nlogin = new Scanner(System.in);
            newname = nlogin.nextLine();

            System.out.println("Please enter the password ");
            Scanner npassword = new Scanner(System.in);
            newpassword = npassword.nextLine();
            System.out.println("the account has been created\n");

        case 2:

            Scanner login = new Scanner(System.in);
            System.out.println("Login:");
            String pass1 = login.nextLine();
            System.out.println("Password:");
            Scanner password = new Scanner(System.in);
            String pass2 = password.nextLine();
            if (pass1 == newname & pass2 == newpassword){
                System.out.println("you are logged in");
            }else{
                System.out.println("incorrect passoword or login");
            }
            break;

        case 3:
            System.out.println("Help is off");
            break;

        case 0:
            System.out.println("ending");
            break;

        default:
            System.out.println("Select the option by pressing 1,2,3 or 0");
            break;
    }
}

---

}这里有很多问题

您缺少一个

中断在第一个案例之后

如果变量只是方法中的局部变量，并且您反复调用该方法，那么在调用之间它们的内容就会被忘记，那么您可能会遇到变量的作用域问题

您正在使用

==

比较字符串，请在此处阅读更多信息=>

正确代码：

public class MainClass {
    String newname = null;
    String newpassword = null;
    //continue your code here
    //call menu() when required
    menu();

}


public void menu()
{
    System.out.println("Hello!");
    System.out.println();
    System.out.println("     ****************************************");
    System.out.println("     *                 MENU                 *");
    System.out.println("     ****************************************");
    System.out.println("     1. Create new account");
    System.out.println("     2. Log in");
    System.out.println("     3. Help");
    System.out.println("     0. End");
    Scanner opcje = new Scanner(System.in);
    int choose = opcje.nextInt();

    switch (choose) 
    {

        case 1:

            System.out.println("You choose create new acount\n Enter the login");
            Scanner nlogin = new Scanner(System.in);
            newname = nlogin.nextLine();

            System.out.println("Please enter the password ");
            Scanner npassword = new Scanner(System.in);
            newpassword = npassword.nextLine();
            System.out.println("the account has been created\n");
            break;

        case 2:

            Scanner login = new Scanner(System.in);
            System.out.println("Login:");
            String pass1 = login.nextLine();
            System.out.println("Password:");
            Scanner password = new Scanner(System.in);
            String pass2 = password.nextLine();
            if (pass1.equals(newname) & pass2.equals(newpassword)){
                System.out.println("you are logged in");
            }else{
                System.out.println("incorrect password or login");
            }
            break;

        case 3:
            System.out.println("Help is off");
            break;

        case 0:
            System.out.println("ending");
            break;

        default:
            System.out.println("Select the option by pressing 1,2,3 or 0");
            break;
    }

}

---

这一行的问题之一是：

   if (pass1 == newname & pass2 == newpassword){
      System.out.println("you are logged in");
     }else{
     System.out.println("incorrect passoword or login");
      }

如果您要调试此代码，您将注意到此

If

语句没有 比较字符串的值。有关更多详细信息，请访问：

请尝试以下代码：

        if(pass1.equals(newname) && pass2.equals(newpassword)) 
        {
            System.out.println("you are logged in");
        }else{
            System.out.println("incorrect passoword or login");
        }

第二个问题：

您需要将switch语句放入

while

循环中：

1.这就是为什么程序不会结束（这样变量）将被保存

---

2.如果用户输入无效，而不是进入默认值，程序也将再次要求用户写入一个数字

尝试更改比较字符串的方式，同时使用java逻辑运算符而不是按位&

static String newname = null;
static String newpassword = null;
public static void main(String[] args) {

    System.out.println("Hello!");
    System.out.println();
    System.out.println("     ****************************************");
    System.out.println("     *                 MENU                 *");
    System.out.println("     ****************************************");
    System.out.println("     1. Create new account");
    System.out.println("     2. Log in");
    System.out.println("     3. Help");
    System.out.println("     0. End");
    Scanner opcje = new Scanner(System.in);
    int choose = opcje.nextInt();

    switch (choose) {

        case 1:

            System.out.println("You choose create new acount\n Enter the login");
            Scanner nlogin = new Scanner(System.in);
            newname = nlogin.nextLine();

            System.out.println("Please enter the password ");
            Scanner npassword = new Scanner(System.in);
            newpassword = npassword.nextLine();
            System.out.println("the account has been created\n");
        case 2:

            Scanner login = new Scanner(System.in);
            System.out.println("Login:");
            String pass1 = login.nextLine();
            System.out.println("Password:");
            Scanner password = new Scanner(System.in);
            String pass2 = password.nextLine();
            //Java uses equals method to compare Strings
            //Java also uses && as the logical operator for "and"
            if (pass1.equals(newname) && pass2.equals(newpassword)) {
                System.out.println("you are logged in");
            } else {
                System.out.println("incorrect password or login");
            }
            break;

        case 3:
            System.out.println("Help is off");
            break;

        case 0:
            System.out.println("ending");
            break;

        default:
            System.out.println("Select the option by pressing 1,2,3 or 0");
            break;
    }
}

---

我不想比较字符串，我想在案例1中全局设置字符串。我认为案例1和案例2之间没有中断。这可能是问题的原因，也可能是因为放断了；在任何情况下，这看起来都像是一个范围问题。这段代码在类中吗？主要的？方法？因为变量是在它里面声明的，所以只要它运行，它们就会一直处于“活动”状态，但一旦它完成，就不会@马辛-这是一个好的开始：@GregArtisi我想他可能错过了

休息有意，因为注册后用户必须登录。这只是我个人的意见！