Delayed Assignment

When you have variables declared inside of that loop cannot be seen from the outside. This poses a problem when you are asking someone a question in a loop but want their response to be visible later on in the program.

One strategy for this is to declare any response-holding variables outside the loop.

The problem with this is that Java isn't smart enough to know that you always initialize those variables.

Scanner scanner = new Scanner(System.in);

String input(String message) {
    System.out.print(message);
    return scanner.nextLine();
}

void main() {
    String name;
    while (true) {
        String name = input("What is your name? ");
        if (name.isBlank()) {
            System.out.println("Name cannot be blank!");
            continue;
        }

        break;
    }

    System.out.println("Hello " + name);
}

To get around this you can either give an explicit default value.

import java.util.Scanner;

Scanner scanner = new Scanner(System.in);

String input(String message) {
    System.out.print(message);
    return scanner.nextLine();
}

void main() {
    String name = null;
    while (true) {
        String name = input("What is your name? ");
        if (name.isBlank()) {
            System.out.println("Name cannot be blank!");
            continue;
        }

        break;
    }

    System.out.println("Hello " + name);
}

Or you can use the do version of a while loop. In this context our old friend delayed assignment becomes an option again. This is because Java is smart enough to see that the code in the loop will run at least once.

import java.util.Scanner;

Scanner scanner = new Scanner(System.in);

String input(String message) {
    System.out.print(message);
    return scanner.nextLine();
}

void main() {
    String name;
    do {
        String name = input("What is your name? ");
        if (name.isBlank()) {
            System.out.println("Name cannot be blank!");
            continue;
        }

        break;
    } while (true);

    System.out.println("Hello " + name);
}