While循环打印线错误

Question

import java.util.Scanner;

public class US_Defense {
    public static void main(String[] args) {
        System.out.println(" ------------------------------------- ");
        System.out.println("  Welcome to the U.S. Defense Network  ");
        System.out.println(" ------------------------------------- ");
        System.out.println("   Please Input your password below.   ");
        System.out.println(" ------------------------------------- ");  


        String pass = "";
        while(!pass.equals("0286139") ){
            System.out.println(" ------------------------------------- ");
            System.out.println("     Incorrect password. Try again.    ");
            System.out.println(" ------------------------------------- ");

            Scanner input = new Scanner(System.in);
            System.out.print("  >: ");
            pass = input.nextLine();
        }
    }
}

When I click run it says the welcome and enter password part, but then it says incorrect password and the user input prompt. I'm trying to have so the code only says welcome and input password but its not doing that.

Answer 1

A do-while loop is probably the cleanest solution. It's a good idea to flush System.out when you print (if you don't include a new-line there isn't an implicit flush). If you really want a while loop you can use the fact that assignment resolves to the right-hand side like:

Scanner input = new Scanner(System.in);
System.out.print("  >: ");
System.out.flush();
String pass;
while (!(pass = input.nextLine()).equals("0286139")) {
    System.out.println(" ------------------------------------- ");
    System.out.println("     Incorrect password. Try again.    ");
    System.out.println(" ------------------------------------- ");

    System.out.print("  >: ");
    System.out.flush();
}

But, a do-while (as mentioned) would be cleaner, and might look like

Scanner input = new Scanner(System.in);
do {
    System.out.print("  >: ");
    System.out.flush();
    String pass = input.nextLine();
    if (pass.equals("0286139")) {
        break;
    }
    System.out.println(" ------------------------------------- ");
    System.out.println("     Incorrect password. Try again.    ");
    System.out.println(" ------------------------------------- ");
} while (true);