Last label of labels array is positioning wrong

Question

I'm trying to create a binary clock in Java using swing. I encountered a problem on very beginning, where last element of label array is always appearing on the 0 x axis position and in the middle of y axis.

I don't want to use any layout menager since i want few circle images on my Panel.

Here's my code so far:

import javax.swing.*;

@SuppressWarnings("serial")
public class MainFrame extends JFrame {

public MainFrame()
{
    setLayout(null);
    JFrame frame = new JFrame("Binary Clock");
    frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
    frame.setVisible(true);
    frame.setSize(600,400);
    frame.setResizable(false);

    JLabel label[] = new JLabel[5];
    for(int i = 0; i < 5; i++)
    {
        label[i] = new JLabel();
        label[i].setLocation(i * 10, i * 10);
        label[i].setSize(30, 10);
        label[i].setText("TEST");
        frame.add(label[i]);
    }       
}

public static void main(String[] args)
{
    new MainFrame();
}
}

i found similar question here:

setLocation of Label

but there is no answer how to do it without layout manager.

I Tried resizing and stuff, but only setText() can do any difference, nothing besides that works.

Thank you!

Answer 1

Pshemo's answer provides the answer as to why you're getting the odd behavior with the last label added, but I've marked up the code with a couple enhancements as well.

1. Remove the extends JFrame, this is rarely a good idea and you already saw why using an instance of a JFrame within a class that is a JFrame can cause...

2. Set the layout of the frame instance to null (rather than that of this) that you have originally. Note: Use of a layout manager is the preferred method to creating Swing UI's, and is generally discouraged to set this to null

3. You don't need the array of labels (unless you plan on using them later), you can just use the loop to add what you want.

4. Make the frame visible last

Then you have:

import javax.swing.*;

@SuppressWarnings("serial")
public class MainFrame {

    public MainFrame()
    {
        JFrame frame = new JFrame("Binary Clock");
        frame.setLayout(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(600,400);
        frame.setResizable(false);

        for(int i = 0; i < 5; i++)
        {
            JLabel label = new JLabel();
            label.setLocation(i * 10, i * 10);
            label.setSize(30, 10);
            label.setText("TEST");
            frame.add(label);
        }

        frame.setVisible(true);
    }

    public static void main(String[] args)
    {
        new MainFrame();
    }
}

Answer 2

I am not Swing specialist so I don't know what consequences will give you null layout manager but from what I remember it is nothing good so consider using proper layout manager instead of null.
Anyway it seems that your problem is caused by fact that you set your null layout in currently initialized by constructor this instance, rather than instance from form regerence.

So instead of

setLayout(null);// represents this.setLayout(..), not frame.setLayout(..)
JFrame frame = new JFrame("Binary Clock");

use

JFrame frame = new JFrame("Binary Clock");
frame.setLayout(null);

I am also not sure why your class extends JFrame. Your code doesn't actually look like it needs any of inherited features from JFrame.

Answer 3

I don't want to use any layout menager since i want few circle images on my Panel.

Swing was designed at the core to use layout managers, it how it's update process works and how it deals with the difference in rendering pipelines across multiple platforms. Sure, you can try and do without it, but in the end, you'd simply reinvent the wheel as you try and compensate for all the little niggly issues that are created while trying to do without it.

The following simply uses a GridBagLayout, which provides me with the ability to supply gridx/y positions to the components (and other nice things)

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.RenderingHints;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JSeparator;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class BinaryClock {

    public static void main(String[] args) {
        new BinaryClock();
    }

    public BinaryClock() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
            setLayout(new GridBagLayout());

            GridBagConstraints gbc = new GridBagConstraints();
            // Hour column
            gbc.gridx = 0;
            addColumn(2, gbc);
            gbc.gridx = 1;
            addColumn(4, gbc);
            // Minute column
            gbc.gridx = 3;
            addColumn(3, gbc);
            gbc.gridx = 4;
            addColumn(4, gbc);
            // Minute column
            gbc.gridx = 6;
            addColumn(3, gbc);
            gbc.gridx = 7;
            addColumn(4, gbc);

            gbc.gridx = 2;
            gbc.gridy = 0;
            gbc.fill = GridBagConstraints.VERTICAL;
            gbc.gridheight = GridBagConstraints.REMAINDER;
            add(new JSeparator(JSeparator.VERTICAL), gbc);

            gbc.gridx = 5;
            add(new JSeparator(JSeparator.VERTICAL), gbc);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        protected void addColumn(int count, GridBagConstraints gbc) {
            for (int index = 0; index < count; index++) {
                gbc.gridy = 3 - index;
                add(new Dot(), gbc);
            }
        }

    }

    public class Dot extends JPanel {

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(100, 100);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.setRenderingHint(RenderingHints.KEY_ALPHA_INTERPOLATION, RenderingHints.VALUE_ALPHA_INTERPOLATION_QUALITY);
            g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
            g2d.setRenderingHint(RenderingHints.KEY_COLOR_RENDERING, RenderingHints.VALUE_COLOR_RENDER_QUALITY);
            g2d.setRenderingHint(RenderingHints.KEY_DITHERING, RenderingHints.VALUE_DITHER_ENABLE);
            g2d.setRenderingHint(RenderingHints.KEY_FRACTIONALMETRICS, RenderingHints.VALUE_FRACTIONALMETRICS_ON);
            g2d.setRenderingHint(RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BILINEAR);
            g2d.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
            g2d.setRenderingHint(RenderingHints.KEY_STROKE_CONTROL, RenderingHints.VALUE_STROKE_PURE);
            g2d.setColor(Color.DARK_GRAY);
            g2d.fillOval(0, 0, getWidth() - 1, getHeight() - 1);
            g2d.dispose();
        }

    }

}

This now frees you up to worry about how to make the clock update without need to continuously try and fix issues in the layout