Displaying multiple lines in Joptionpane?

Question

Hi Im new to this forum and also new to java, I need some help for my intro to java homework. Ive done most of the logic. The problem is to write a program that displays all the numbers from 100 to 1000, ten per line, that are divisible by 5 and 6. Numbers are separated by exactly one space. My professor wants it to be done in a Joptionpane window. When I try to do that, only one answer pops up in a window. How do I make my answers appear ten in a line, separated by exactly one space in only one window? My professor wants us to use an escape function to be able to display the lines of answer.

public class FindFactors {
    public static void main(String[] args) {
        String message = "";
        final int NumbersPerLine = 10;    // Display 10 numbers per line
        int count = 0; // Count the number of numbers divisible by 5 and 6

        // Test all numbers from 100 to 1,000

        for (int i = 100; i <= 1000; i++) {
            // Test if number is divisible by 5 and 6
            message = message + " " + i;
            count++;
            if (count == 10) {
                message = message + "\r\n";
                count = 0;
            }
            if (i % 5 == 0 && i % 6 == 0) {
                count++;    // increment count
                // Test if numbers per line is 10
                if (count % NumbersPerLine == 0)
                    JOptionPane.showMessageDialog(null, i);
                else
                    JOptionPane.showMessageDialog(null, (i + " "));
            }
        }
    }
}

Answer 1

Please see the below approach, a slight change to your code and will give the required output.

public class FindFactors {
public static void main(String[] args) {
final int NumbersPerLine = 10;    // Display 10 numbers per line
int count = 0; // Count the number of numbers divisible by 5 and 6
// Test all numbers from 100 to 1,000
String numbersPerLine = "";
for (int i = 100; i <= 1000; i++) {
    // Test if number is divisible by 5 and 6
    if (count == 10) {           
        count = 0;
    }
    if (i % 5 == 0 && i % 6 == 0) {
        numbersPerLine =numbersPerLine+" "+i;
        count++;    // increment count
        // Test if numbers per line is 10

        if (count % NumbersPerLine == 0) 
            numbersPerLine =numbersPerLine+"\n";
    }
}
JOptionPane.showMessageDialog(null, numbersPerLine);
}
}

Answer 2

A JOptionPane has the ability to show images, text or any other components, for this particular case you may want to create your own JPanel which adds every line of numbers into a JLabel and then adds that JLabel to it.

import javax.swing.BoxLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class MultiLineOptionPane {
    private JPanel pane;

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new MultiLineOptionPane()::createAndShowGui);
    }

    public void createAndShowGui() {
        pane = new JPanel();
        pane.setLayout(new BoxLayout(pane, BoxLayout.PAGE_AXIS));

        StringBuilder sb = new StringBuilder(); //This object will be used to concatenate in the next for loop
        for (int i = 0; i < 500; i++) { //Sample for loop
            if ((i) % 10 == 0) { //Every 10 numbers we restart the StringBuilder
                pane.add(new JLabel(sb.toString())); //We add a new JLabel to the JPanel with the contents of the StringBuilder
                sb.delete(0, sb.length()); //We restart the StringBuilder
            } else {
                sb.append(i); //We append the current number to the StringBuilder
                sb.append(" "); //We append a space after the number
            }
        }
        pane.add(new JLabel(sb.toString())); //We add the last line of numbers in the StringBuilder to the pane

        JOptionPane.showMessageDialog(new JFrame(), pane, "Numbers", JOptionPane.PLAIN_MESSAGE); //We display the message
    }
}

The output for the above program looks like (cropped or it would be too tall):