Add JButton array to a JPanel (buttons not visible)

Question

I'm trying to create a simple calculator with Java. For that purpose I created an array of JButton and added them to the JPanel.

The issue: the buttons are not visible.

I also added a single JLabel and a single JButton for testing, and they show up correctly.

The code:

package test;

import java.awt.BorderLayout;
import javax.swing.*;

public class Test {

    JLabel testLabel = new JLabel("Test label", SwingConstants.CENTER);
    JButton testButton = new JButton("Test button");

    JButton buttons[];

    Test() {

        JFrame frame = new JFrame("Calculator");

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JPanel panel = new JPanel();  

        for (int i = 0; i > 15; i++) {

            buttons[i] = new JButton(Integer.toString(i));
            panel.add(buttons[i], BorderLayout.CENTER);

        }

        panel.add(testButton, BorderLayout.CENTER);
        panel.add(testLabel, BorderLayout.CENTER);

        frame.setSize(500, 500);

        frame.add(panel, BorderLayout.CENTER);

        frame.setVisible(true);
    }


    public static void main(String[] args) {

        Test cTest = new Test();

    }

}

What am I doing wrong?

Note that the default layout manager of a JPanel is FlowLayout , not BorderLayout . — Arnaud
– Arnaud, Commented Jul 16, 2018 at 9:54
Note2: if the layout manager of the panel was set to BorderLayout, you still would only see the last component since all are being added with BorderLayout.CENTER — user85421
– user85421, Commented Jul 16, 2018 at 10:05

am9417 · Accepted Answer · 2018-07-16 10:05:32Z

2

The problem is that the condition in your for loop is invalid. Replace the > with <: The statement 0 > 15 is never is never evaluated to true which is why your loop never starts iterating:

for(int i = 0; i < 15; i++)

Also you must create the array with new keyword before you assign items to it. Otherwise you will get a NullPointerException:

buttons = new JButton[15];

edited Jul 16, 2018 at 10:05

answered Jul 16, 2018 at 9:55

am9417

1,04613 silver badges21 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Dimitrije Milenkovic · Accepted Answer · 2018-07-16 10:00:25Z

2

First, I think that your for loop should like like this

for (int i = 0; i < 15; i++)

And after that, in you have to initialize your buttons reference

JButton buttons[] = new JButton[15];

answered Jul 16, 2018 at 10:00

Dimitrije Milenkovic

536 bronze badges

Comments

M'aiq the Coder · Accepted Answer · 2018-07-16 10:36:57Z

0

Usually when you use a for loop you have to initialise your objects for every single loop. If you have a TextView for example, you'll have to do:

TextHeaders[i] = new TextView([activity_name].this);

For your problem,

buttons[i] = new JButton (this);

answered Jul 16, 2018 at 10:36

M'aiq the Coder

82210 silver badges19 bronze badges

Collectives™ on Stack Overflow

Add JButton array to a JPanel (buttons not visible)

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related