Java Swing

Hello

I'm an Apprentice in 2nd year and I've just learned about Swing.
Currently my task is to experiment and try to make something.
First I made a rapid prototype.

Here is the Code to the Prototype:

package src; import java.awt.BorderLayout; import java.awt.Dimension; import java.awt.FlowLayout; import javax.swing.BoxLayout; import javax.swing.JButton; import javax.swing.JCheckBox; import javax.swing.JComboBox; import javax.swing.JFrame; import javax.swing.JPanel; import javax.swing.JScrollPane; import javax.swing.JTextArea; import javax.swing.JTextField; public class Main { public static void main(String[] args) { JFrame frame = new JFrame("Aufgab 5.5 - Design"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setLayout(new BorderLayout(10,10)); JPanel topPanel = new JPanel(); topPanel.setLayout(new FlowLayout(FlowLayout.LEFT)); String[] pets = { "bird", "dog", "cat"}; JComboBox<String> petComboBox = new JComboBox<String>(pets); topPanel.add(petComboBox); frame.add(topPanel, BorderLayout.NORTH); JTextArea textArea = new JTextArea("TextArea"); JScrollPane scrollPane = new JScrollPane(textArea); scrollPane.setPreferredSize(new Dimension(250,60)); frame.add(scrollPane, BorderLayout.CENTER); JPanel eastPanel = new JPanel(); eastPanel.setLayout(new BoxLayout(eastPanel, BoxLayout.Y_AXIS)); JCheckBox checkBox1 = new JCheckBox("Check I"); JCheckBox checkBox2 = new JCheckBox("Check II"); JCheckBox checkBox3 = new JCheckBox("Check III"); JCheckBox checkBox4 = new JCheckBox("Check IV"); eastPanel.add(checkBox1); eastPanel.add(checkBox2); eastPanel.add(checkBox3); eastPanel.add(checkBox4); frame.add(eastPanel, BorderLayout.EAST); JPanel southPanel = new JPanel(); southPanel.setLayout(new FlowLayout(FlowLayout.LEFT)); JTextField textField = new JTextField("TextField"); JButton button1 = new JButton("Button 1"); JButton button2 = new JButton("Button 2"); southPanel.add(textField); southPanel.add(button1); southPanel.add(button2); frame.add(southPanel, BorderLayout.SOUTH); frame.pack(); frame.setVisible(true); } }

This is what the prototype looked like and then i tried to do a second version of it and trying to refactor and use best practices.

Here is the updated version:

Main.java
package src; import javax.swing.SwingUtilities; public class Main { public static void main(String[] args) { SwingUtilities.invokeLater(() -> { MainWindow mwd = new MainWindow("Aufgabe 5.5 - Erweitert"); mwd.setVisible(true); }); } }

MainWindow.java
package src; import java.awt.BorderLayout; import javax.swing.JFrame; public class MainWindow extends JFrame { private static final TopPanel topPanel = new TopPanel(); private static final CenterPanel centerPanel = new CenterPanel(); private static final EastPanel eastPanel = new EastPanel(); private static final SouthPanel southPanel = new SouthPanel(); public MainWindow(String frameTitle) { super(frameTitle); setDefaultCloseOperation(EXIT_ON_CLOSE); setLayout(new BorderLayout(10,10)); add(topPanel, BorderLayout.NORTH); add(centerPanel, BorderLayout.CENTER); add(eastPanel, BorderLayout.EAST); add(southPanel, BorderLayout.SOUTH); pack(); setLocationRelativeTo(null); } }

CenterPanel.java
package src; import java.awt.Dimension; import javax.swing.JPanel; import javax.swing.JScrollPane; import javax.swing.JTextArea; public class CenterPanel extends JPanel { private static final JTextArea jTextArea = new JTextArea("TextArea"); private static final JScrollPane jScrollPane = new JScrollPane(jTextArea); public CenterPanel() { jScrollPane.setPreferredSize(new Dimension(250,90)); add(jScrollPane); } }

EastPanel.java
package src; import java.awt.List; import javax.swing.BoxLayout; import javax.swing.JCheckBox; import javax.swing.JPanel; public class EastPanel extends JPanel { private static final JCheckBox c1 = new JCheckBox("Check I"); private static final JCheckBox c2 = new JCheckBox("Check II"); private static final JCheckBox c3 = new JCheckBox("Check III"); private static final JCheckBox c4 = new JCheckBox("Check IV"); private static final JCheckBox[] checkboxes = {c1,c2,c3,c4}; public EastPanel() { setLayout(new BoxLayout(this, BoxLayout.Y_AXIS)); for (JCheckBox checkbox : checkboxes) { add(checkbox); } } }

SouthPanel.java
package src; import java.awt.FlowLayout; import javax.swing.JButton; import javax.swing.JPanel; import javax.swing.JTextField; public class SouthPanel extends JPanel{ private static final JTextField jTextfield = new JTextField("TextField"); private static final JButton jbutton1 = new JButton("Button 1"); private static final JButton jbutton2 = new JButton("Button 2"); public SouthPanel() { setLayout(new FlowLayout(FlowLayout.LEFT)); add(jTextfield); add(jbutton1); add(jbutton2); } }

TopPanel.java
package src; import java.awt.FlowLayout; import javax.swing.JComboBox; import javax.swing.JPanel; public class TopPanel extends JPanel { private static final String[] pets = { "Bird", "Dog", "Cat", "Hedgehog" }; private static final JComboBox<String> petComboBox = new JComboBox<String>(pets); public TopPanel() { setLayout(new FlowLayout(FlowLayout.LEFT)); add(petComboBox); } }

I used static on the components since my job was to make a single page with some stuff on it since it wouldn't change and i don't need to add something.

What can I do better or what should i change?

Kind Regards
Vijiyarathan Rithush

hi Vijiyarathan,

two remarks that I want to make:

1) never make a variable static unless absolutely necessary! Even if you intend to never change them.
2) in your MainWindow you have the fields topPanel, et cetera. Nothing wrong with that, but do you need these references? If not, then you might as well do (in the constructor)
add(new TopPanel(), BorderLayout.PAGE_START);
I prefer PAGE_START over NORTH, because NORTH is absolute, while PAGE_START takes the Locale into consideration: if a locale has a page going from bottom to top. then PAGE_START will put the panel at the bottom. But that is just a minor detail.

Thanks for the info!

I've talked with my teacher and he said I shouldn't let the classes inherit. He said something about composition over inheritance too, so i tried to implement it.
I'll try your tips as well.

This is the current state of my code:

Main.java
package src; import javax.swing.SwingUtilities; public class Main { public static void main(String[] args) { SwingUtilities.invokeLater(() -> { MainWindow mwd = new MainWindow("Aufgabe 5.5 - Erweitert"); mwd.setVisible(true); }); } }

MainWindow.java
package src; import java.awt.BorderLayout; import javax.swing.JFrame; public class MainWindow { private final JFrame frame; private final TopPanel topPanel; private final CenterPanel centerPanel; private final EastPanel eastPanel; private final SouthPanel southPanel; public MainWindow(String frameTitle) { frame = new JFrame(frameTitle); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setLayout(new BorderLayout(10,10)); topPanel = new TopPanel(); centerPanel = new CenterPanel(); eastPanel = new EastPanel(); southPanel = new SouthPanel(); frame.add(topPanel.getComponent(), BorderLayout.NORTH); frame.add(centerPanel.getComponent(), BorderLayout.CENTER); frame.add(eastPanel.getComponent(), BorderLayout.EAST); frame.add(southPanel.getComponent(), BorderLayout.SOUTH); frame.pack(); frame.setLocationRelativeTo(null); } public JFrame getComponent() { return frame; } public void setVisible(boolean visible) { frame.setVisible(visible); } }

TopPanel.java
package src; import java.awt.FlowLayout; import javax.swing.JComboBox; import javax.swing.JPanel; public class TopPanel { private final JPanel panel; private final String[] pets = { "Bird", "Dog", "Cat", "Hedgehog" }; private final JComboBox<String> petComboBox = new JComboBox<String>(pets); public TopPanel() { panel = new JPanel(); panel.setLayout(new FlowLayout(FlowLayout.LEFT)); panel.add(petComboBox); } public JPanel getComponent() { return panel; } }

SouthPanel.java
package src; import java.awt.FlowLayout; import javax.swing.JButton; import javax.swing.JPanel; import javax.swing.JTextField; public class SouthPanel { private final JPanel panel; private final JTextField jTextfield = new JTextField("TextField"); private final JButton jbutton1 = new JButton("Button 1"); private final JButton jbutton2 = new JButton("Button 2"); public SouthPanel() { panel = new JPanel(); panel.setLayout(new FlowLayout(FlowLayout.LEFT)); panel.add(jTextfield); panel.add(jbutton1); panel.add(jbutton2); } public JPanel getComponent() { return panel; } }

CenterPanel.java
package src; import java.awt.Dimension; import javax.swing.JPanel; import javax.swing.JScrollPane; import javax.swing.JTextArea; public class CenterPanel { private final JPanel panel; private final JTextArea textArea; private final JScrollPane jScrollPane; public CenterPanel() { panel = new JPanel(); textArea = new JTextArea(); jScrollPane = new JScrollPane(textArea); jScrollPane.setPreferredSize(new Dimension(250,95)); panel.add(jScrollPane); } public JPanel getComponent() { return panel; } }

EastPanel.java
package src; import javax.swing.BoxLayout; import javax.swing.JCheckBox; import javax.swing.JPanel; public class EastPanel { private final JPanel panel; private final JCheckBox c1 = new JCheckBox("Check I"); private final JCheckBox c2 = new JCheckBox("Check II"); private final JCheckBox c3 = new JCheckBox("Check III"); private final JCheckBox c4 = new JCheckBox("Check IV"); private final JCheckBox[] checkboxes = {c1,c2,c3,c4}; public EastPanel() { panel = new JPanel(); panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS)); for (JCheckBox checkbox : checkboxes) { panel.add(checkbox); } } public JPanel getComponent() { return panel; } }

Let me know if there is anything else i should know or learn!

I am pleased to see you aren't using extends any more. Your application usually ISN'T‑A‑JFrame, but it HAS‑A‑JFrame. It may be a good idea to change your fields to be local variables in the constructor or (maybe better) a setUpGUI() method. That will give you access to them, as Piet mentioned.

I shall move you to our forum where we usually discuss GUIs.

What do you mean by using the setupGUI method. I'm asking myself what it means.

What my teacher also mentioned is that i had a getComponent() in the MainWindow.java class, which enabled me to execute ALL the other methods there is, but I only need the getComponent() method.

You are doing the layout in the constructor. That is fine, and I always do that. Some people prefer to do the layout in a separate method, usually called setUpGUI. And when you use a dedicated GUI-builder, well these also work with a separate setUpGUI-method. Whether to use this or not, that is a personal preference.

Your code looks much better now! You call your method 'getComponent', I would prefer 'getPanel' instead, is more clear, and 'getFrame' for the main class. I would even go one step further. For instance in your EastPanel-class, I would make the constructor private, so that you cannot create directly an instance. Instead, I would have the method 'getPanel' as follows:
public static JPanel getPanel() {    var temp = new EastPanel();    return temp.panel; }
and then in MainPanel:
eastPanel = EastPanel.getPanel();
But this is what I would prefer. You could do exactly the same for your MainWindow, so in Main:
SwingUtilities.invokeLater( () -> MainWindow.getFrame().setVisible(true));

Thanks for the info!

I'm wondering why you can do this:

public static JPanel getPanel() {    var temp = new EastPanel();    return temp.panel; }

How can I come up with this since I never knew that you can do that.

I will provide my updated code. Please look if i can do something better coding wise...

Main.java
package src; import javax.swing.SwingUtilities; public class Main { public static void main(String[] args) { SwingUtilities.invokeLater(() -> MainWindow.setVisible(true)); } }

MainWindow.java
package src; import java.awt.BorderLayout; import javax.swing.JFrame; import javax.swing.JPanel; public class MainWindow { private final JFrame frame; private final JPanel topPanel; private final JPanel centerPanel; private final JPanel eastPanel; private final JPanel southPanel; private MainWindow() { frame = new JFrame("Aufgabe 5.5"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setLayout(new BorderLayout(10,10)); topPanel = TopPanel.getPanel(); centerPanel = CenterPanel.getPanel(); eastPanel = EastPanel.getPanel(); southPanel = SouthPanel.getPanel(); frame.add(topPanel, BorderLayout.PAGE_START); frame.add(centerPanel, BorderLayout.CENTER); frame.add(eastPanel, BorderLayout.EAST); frame.add(southPanel, BorderLayout.SOUTH); frame.pack(); frame.setLocationRelativeTo(null); } private static JFrame getFrame() { var temp = new MainWindow(); return temp.frame; } public static void setVisible(boolean visible) { MainWindow.getFrame().setVisible(true); } }

TopPanel.java
package src; import java.awt.Color; import java.awt.FlowLayout; import javax.swing.JComboBox; import javax.swing.JPanel; public class TopPanel { private final JPanel panel; private final String[] pets = { "Bird", "Dog", "Cat", "Hedgehog" }; private final JComboBox<String> petComboBox = new JComboBox<String>(pets); private TopPanel() { panel = new JPanel(); panel.setLayout(new FlowLayout(FlowLayout.LEFT)); panel.add(petComboBox); panel.setBackground(Color.RED); } public static JPanel getPanel() { var temp = new TopPanel(); return temp.panel; } }

SouthPanel.java
package src; import java.awt.Color; import java.awt.FlowLayout; import javax.swing.JButton; import javax.swing.JPanel; import javax.swing.JTextField; public class SouthPanel { private final JPanel panel; private final JTextField jTextfield = new JTextField("TextField"); private final JButton jbutton1 = new JButton("Button 1"); private final JButton jbutton2 = new JButton("Button 2"); private SouthPanel() { panel = new JPanel(); panel.setLayout(new FlowLayout(FlowLayout.LEFT)); panel.add(jTextfield); panel.add(jbutton1); panel.add(jbutton2); panel.setBackground(Color.BLUE); } public static JPanel getPanel() { var temp = new SouthPanel(); return temp.panel; } }

EastPanel.java
package src; import java.awt.Color; import javax.swing.BoxLayout; import javax.swing.JCheckBox; import javax.swing.JPanel; public class EastPanel { private final JPanel panel; private final JCheckBox c1 = new JCheckBox("Check I"); private final JCheckBox c2 = new JCheckBox("Check II"); private final JCheckBox c3 = new JCheckBox("Check III"); private final JCheckBox c4 = new JCheckBox("Check IV"); private final JCheckBox[] checkboxes = {c1,c2,c3,c4}; private EastPanel() { panel = new JPanel(); panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS)); for (JCheckBox checkbox : checkboxes) { panel.add(checkbox); } panel.setBackground(Color.GREEN); } public static JPanel getPanel() { EastPanel temp = new EastPanel(); return temp.panel; } }

CenterPanel.java
package src; import java.awt.Color; import javax.swing.JPanel; import javax.swing.JScrollPane; import javax.swing.JTextArea; public class CenterPanel { private final JPanel panel; private final JTextArea textArea; private final JScrollPane jScrollPane; public CenterPanel() { panel = new JPanel(); textArea = new JTextArea(); jScrollPane = new JScrollPane(textArea); panel.add(jScrollPane); panel.setBackground(Color.YELLOW); } public static JPanel getPanel() { var temp = new CenterPanel(); return temp.panel; } }

The main thing i want to know is how I personally can come up with these solutions you came up with.

May I also like get a code review. I wanna know what i did good and what i could improve on.

Thanks in advance!

Piet Souris wrote:hi Vijiyarathan,

two remarks that I want to make:

1) never make a variable static unless absolutely necessary! Even if you intend to never change them.
2) in your MainWindow you have the fields topPanel, et cetera. Nothing wrong with that, but do you need these references? If not, then you might as well do (in the constructor)
add(new TopPanel(), BorderLayout.PAGE_START);
I prefer PAGE_START over NORTH, because NORTH is absolute, while PAGE_START takes the Locale into consideration: if a locale has a page going from bottom to top. then PAGE_START will put the panel at the bottom. But that is just a minor detail.

I don't know of any locales where displays run from bottom to top, but left-to-right/right-to-left is a thing. But I wouldn't recommend EAST or WEST for that.

Of course, old-time European traditionalists all know that the proper location of map direction is with Jerusalem at the centre, and East may be at the top.

You're welcome!

Your code looks very fine to me! I would change one thing, though. Lets look at the CenterPanel class. You have three private final fields. That is fine, but if you look at the code, you see that you only need a reference for the panel, since we return that in the 'getPanel' method. We do not need a reference for the other two fields, so we can create them in the constructor. So we would get:
public class CenterPanel {    private final JPanel panel;    private CenterPanel()    {        panel = new JPanel();        var textArea = new JTextArea();        var jScrollPane = new JScrollPane(textArea);        panel.add(jScrollPane);        panel.setBackground(Color.YELLOW);    }        public static JPanel getPanel()    {        var temp = new CenterPanel();        return temp.panel;    } }

Vijiyarathan wrote:
The main thing i want to know is how I personally can come up with these solutions you came up with.

Experience and personal preferences. I like to use static factory-methods to create instances, and so I use that the last couple of years whenever that is handy. But nothing wrong with the new ...  construction! Use that if that is what you prefer.

If I want to learn things like these. Where can i read or watch something about this?

I am usually dubious about things found online; YouiTube is full of pretty poor tutorials. Baeldung is an exception; his site is good. It is probably worth your while getting a copy of Effective Java by Jshia Bloch [Sun Microsystems Press/Addison‑Wesley/Pearson]. Get the 3rd edition if possible, which came out about 2017. You will find a discussion of the advantages of factory methods in §1.
I think I might not use a factory method for that panel; all you are doing is adding components to it. I think you can do that as simply without that method. This goes to show there are usually several different ways to program your app. You could however consider a method like getPanelWithScrollPane() which will create the thing for you complete with scroll pane. You could pass the component to put inside the scroll pane as an argument by changing the parameters to such a method.