Swing/AWT ¶

Swing and AWT are libraries bundled with Java to create graphical interfaces. Swing was introduced as a replacement for AWT, but it didn't completely replace AWT.

☠️ Modern developers prefer to use JavaFX, which heavily cuts down the quantity of code, and the time invested for the same output.

These are the two base packages:

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

👉 Swing classes usually start with J followed by their AWT name.

A component is a graphical entity such as a Button.

All Swing components are extending JComponent while AWT components are extending Component.

JComponent aComponent = new JButton();

Child components

aComponent.add(anotherOne);
aComponent.remove(anotherOne);
aComponent.removeAll();

Drawing

aComponent.repaint();        // redraw if modified
aComponent.revalidate();     // force redraw

aComponent.setVisible(true); // show

Style

aComponent.setFont(new Font("name", Font.PLAIN, 20));
aComponent.setOpaque(true); // mark as having a background
aComponent.setBackground(Color.RED); // background color if opaque
aComponent.setForeground(Color.WHITE); // text color

Size

// DO NOT USE setSize, it's ignored by most layouts
aComponent.setPreferredSize(new Dimension(50,50));
// MAY BE IGNORED by the layout
aComponent.setSize(new Dimension(50,50));
aComponent.setMinimumSize(new Dimension(50,50));
aComponent.setMaximumSize(new Dimension(50,50));

JFrame - window ¶

You'll usually create a frame, and add a component inside. Then, you'll make it visible.

JFrame f = new JFrame("title");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); // when "x" pressed
f.setSize(500,500); // size
f.setLocation(0,0); // location in the screen
f.add(component);   // add ONE component, usually a JPanel
f.setVisible(true); // show, false by default

JLabel - a text ¶

JLabel label = new JLabel("text");
label.setHorizontalAlignment(JLabel.CENTER);
label.setText("xxxx");
String text = label.getText();

JButton - a button ¶

JButton b = new JButton("test");
b.addActionListener( /* refer to listeners */ );

Input fields ¶

• JTextArea: a text input zone
• JTextField: a text input field
• JPassword: a password input field
• JCheckBox: a checkbox input field
• JRadioButton: a radio button
• JList: a select list

JPanel - group elements ¶

We usually put components in a JPanel, allowing us to perform an action (move, show/hide) on the whole group.

JPanel p = new JPanel();
p.add(xxx);               // add "xxx" to the group

👉 See also: JScrollPane for a scrollable panel.

Layout Managers determine how child components are displayed. They are commonly used with JPanel 🖼️.

// some constructors can take a layout manager too
aComponent.setLayout(LayoutManager);

By default, the layout manager is a FlowLayout.

FlowLayout ¶

In the FlowLayout, each component takes its preferred size. Elements could be aligned to the left, to the right, or to the center (default).

aComponent.setLayout(new FlowLayout(FlowLayout.LEFT));

BorderLayout ¶

The BorderLayout divides the container into 5 areas. The center takes up the remaining space. North and South expand as much as possible horizontally. East and West expand as much as possible vertically.

aComponent.setLayout(new BorderLayout());
aComponent.add(component1, BorderLayout.NORTH);
aComponent.add(component2, BorderLayout.SOUTH);
aComponent.add(component3, BorderLayout.CENTER); // default
aComponent.add(component4, BorderLayout.EAST);
aComponent.add(component5, BorderLayout.WEST);

GridBagLayout ¶

GridBagLayout is the most versatile layout. Before adding a component, you'll define the constraint on it (position...).

aComponent.setLayout(new GridBagLayout());

GridBagConstraints c = new GridBagConstraints();
c.gridx = 0; c.gridy = 0;                  // position
c.gridwidth = 1; c.gridheight = 1;         // colspan/rowspan
c.weightx = 0; c.weighty = 0;              // expand priority
c.anchor = GridBagConstraints.LINE_START;  // alignement
c.fill = GridBagConstraints.HORIZONTAL;    // expand behavior
c.insets = new Inset(top, left, bottom, right);  // padding

aComponent.add(someComponent, c);

GridLayout ¶

In a GridLayout, all rows/columns have the same width/height.

aComponent.setLayout(new GridLayout(rowCount, colCount));

CardLayout ¶

In a CardLayout, we can swap the content displayed with another view.

CardLayout cardLayout = new CardLayout();
aComponent.setLayout(cardLayout);
aComponent.add("key", view);        // adding a view
cardLayout.show(aComponent, "key"); // select a view
cardLayout.first(aComponent);       // show the first view
cardLayout.next(aComponent);        // show the next view
cardLayout.previous(aComponent);    // show the previous view

Listeners allow us to react when the user interacts with the view, such as by clicking on a button.

aComponent.addMouseListener(/* a listener here */);
aComponent.removeMouseListener(/* a listener here */);
aButton.addActionListener(/* a listener here */);
aJFrame.addWindowListener(/* a listener here */);
// see also: MouseMotionListener, MouseWheelListener...

Mouse listener ¶

You can also use MouseAdapter (abstract class) implementing MouseListener, MouseWheelListener, and MouseMotionListener.

public class MyMouseListener implements MouseListener {
    @Override // click
    public void mouseClicked(MouseEvent e){}
    @Override // hover (entering)
    public void mouseEntered(MouseEvent e){}
    @Override // hover (exiting)
    public void mouseExited(MouseEvent e){}
    @Override
    public void mousePressed(MouseEvent e){}
    @Override
    public void mouseReleased(MouseEvent e){}
}

Action listener ¶

This listener is called when a button is pressed.

// public class MyActionListener implements ActionListener
// public void actionPerformed(ActionEvent e)
aButton.addActionListener(e -> {
    // get the button (if needed)
    Object source = e.getSource();
    JButton button = (JButton) source;
    // get the text of the button (if needed)
    String text = e.getActionCommand();
    // ...
});

Window listener ¶

You can also use WindowAdapter (abstract class) implementing WindowListener, WindowStateListener, and WindowFocusListener

public class MyWindowListener implements WindowListener {
    @Override // never called?
    public void windowClosed(WindowEvent e){}
    @Override // before closing
    public void windowClosing(WindowEvent e){}
    @Override
    public void windowActivated(WindowEvent e){}
    @Override
    public void windowDeactivated(WindowEvent e){}
    @Override
    public void windowIconified(WindowEvent e){}
    @Override
    public void windowDeiconified(WindowEvent e){}
    @Override // never called?
    public void windowOpened(WindowEvent e){}
}

You can draw your own component by extending JComponent and overriding paintComponent.

import javax.swing.JComponent;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Font;
import java.awt.RenderingHints;

public class Demo extends JComponent {

    @Override
    protected void paintComponent(Graphics g) {
        // make a copy just in case
        Graphics2D copy = (Graphics2D) g.create();

        // do not draw a background if not opaque
        if (isOpaque()) {
            copy.setColor(getBackground());
            copy.fillRect(0, 0, getWidth(), getHeight());
        }

        // ...
    }
}

Some parts of code you might use:

// drawing options
RenderingHints rh = new RenderingHints(
    RenderingHints.KEY_ANTIALIASING,
    RenderingHints.VALUE_ANTIALIAS_OFF);
copy.setRenderingHints(rh);

// color, font, ...
copy.setColor(Color.RED);
copy.setFont(new Font("name", Font.PLAIN, 20));

// forms
copy.drawLine(int x1, int y1, int x2, int y2);
copy.drawPolygon( int[] xPoints, int[] yPoints, int nPoints);
copy.drawRect(int x, int y, int width, int height);
// ...

// images
// (Toolkit.getDefaultToolkit().getImage(path) ???)
copy.drawImage(Image img, int x, int y, ImageObserver observer)

• Event thread
• SwingUtilities.invokeLater(Runnable);
• JOptionPane, JFileChooser