Ndtyjky

I'm not sure it is possible, because I haven't found exact answer, but NetBeans not gives error. But if it's possible, why my code doesn't work?

public static void main(String args) {

    Scanner scan = new Scanner(System.in);



    int fiveMatrix = {

        {1, 4, 7, 5, 3}, {3, 7, 9, 10, 1}, {4, -3, 2, -4, 1}, {5, 9, 6, 4, 3}, {1, 2, 3, 4, 5},};



    System.out.print("Which line do you want to write out (0-4)? ");

    int lineNumber = scan.nextInt();

    boolean goodLine = lineNumber < 0 || lineNumber > 4;

    if (goodLine) {

        while (goodLine) {

            System.out.println("Bad index.");

            System.out.print("Which line do you want to write out (0-4)? ");

            lineNumber = scan.nextInt();

        }

    }

}

}

This here:

boolean goodLine = lineNumber < 0 || lineNumber > 4;

is evaluated once, and the result is assigned to that variable.

Later changes to lineNumber = scan.nextInt(); do not change that boolean variable!

The "correct" solution: you have to recompute the boolean property. But ideally not by copying code, but by creating a small helper method:

boolean isGoodLine(int lineNumber) { return lineNumber < 0 || lineNumber > 4; }

And now, instead of having a boolean variable in your other code, you simply invoke that method whenever the lineNumber changes!

You probably want to update the boolean inside the loop, to avoid infinite loop.

boolean badLine = lineNumber < 0 || lineNumber > 4;

while (badLine) {

    System.out.println("Bad index.");

    System.out.print("Which line do you want to write out (0-4)? ");

    lineNumber = scan.nextInt();

    badLine = lineNumber < 0 || lineNumber > 4;

}

I renamed the boolean, since its original name was confusing. I also eliminated the if condition, since it's redundant.

You are missing a line inside while loop

boolean goodLine = lineNumber < 0 || lineNumber > 4;

Consider refactor to a method to avoid duplicate code:

public boolean goodLine(Scanner scan) {

    System.out.print("Which line do you want to write out (0-4)? ");

    int lineNumber = scan.nextInt();

    return lineNumber < 0 || lineNumber > 4;

}

And call it:

while(goodLine());

Consider also call it a badLine because user input is wrong (not 0-4 values)

Simplified code and easy to understand

import java.util.Scanner;



public class Post3 {



    public static void main(String args) {

        Scanner scan = new Scanner(System.in);



        int fiveMatrix = {

            {1, 4, 7, 5, 3}, {3, 7, 9, 10, 1}, {4, -3, 2, -4, 1}, {5, 9, 6, 4, 3}, {1, 2, 3, 4, 5},};



        System.out.println("Which line do you want to write out (0-4)? ");

        int input = -1;

        while(true) {

            System.out.println("input valid number between 0 to 4");

            input = scan.nextInt();

            if(input >= 0 && input <= 4) {

                break;

            }

        }

        System.out.println("input is "+input);

        scan.close();



    }



}