Continues Covering Basic Java Swing components

Continues Covering Basic Java Swing components

Swing components are basic building blocks of an application. Swing toolkit has a wide range of various components. Buttons, check boxes, sliders, list boxes etc. Everything a programmer needs for his job. In this section of the tutorial, we will describe several useful components.

JList Component

JList is a component that displays a list of objects. It allows the user to select one or more items.

package zetcode;

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.GraphicsEnvironment;

import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.SwingUtilities;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.ListSelectionListener;


public class ListExample extends JFrame {

    private JLabel label;
    private JList list;


    public ListExample() {

        initUI();
    }

    public final void initUI() {

        JPanel panel = new JPanel();
        panel.setLayout(new BorderLayout());
        panel.setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));

        GraphicsEnvironment ge =
            GraphicsEnvironment.getLocalGraphicsEnvironment();

        String[] fonts = ge.getAvailableFontFamilyNames();

        list = new JList(fonts);
        list.addListSelectionListener(new ListSelectionListener() {
            public void valueChanged(ListSelectionEvent e) {
                if (!e.getValueIsAdjusting()) {
                    String name = (String) list.getSelectedValue();
                    Font font = new Font(name, Font.PLAIN, 12);
                    label.setFont(font);
                }
            }
        });

        JScrollPane pane = new JScrollPane();
        pane.getViewport().add(list);
        pane.setPreferredSize(new Dimension(250, 200));
        panel.add(pane);

        label = new JLabel("Aguirre, der Zorn Gottes");
        label.setFont(new Font("Serif", Font.PLAIN, 12));
        add(label, BorderLayout.SOUTH);


        add(panel);

        pack();
        setTitle("JList");
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
    }

    public static void main(String[] args) {
        
        SwingUtilities.invokeLater(new Runnable() {

            public void run() {
                ListExample ex = new ListExample();
                ex.setVisible(true);
            }
        });
    }
}

In our example, we will display a JList and a JLabel components. The list component contains a list of all available font family names on our system. If we select an item from the list, the label will be displayed in a font, we have chosen.

GraphicsEnvironment ge = 
    GraphicsEnvironment.getLocalGraphicsEnvironment();

String[] fonts = ge.getAvailableFontFamilyNames();

Here we obtain all possible font family names on our system.

list = new JList(fonts);

We create a JList component.

public void valueChanged(ListSelectionEvent e) {
    if (!e.getValueIsAdjusting()) {

Events in list selection are grouped. We receive events for both selecting and deselecting. To filter only the selecting events, we use the getValueIsAdjusting() method.

String name = (String) list.getSelectedValue();
Font font = new Font(name, Font.PLAIN, 12);
label.setFont(font);

We get the selected item and set a new font for the label.

JScrollPane pane = new JScrollPane();
pane.getViewport().add(list);

JLabel component is not scrollable by default. We put the list into the JScrollPane to make it scrollable.

Figure: JList

JTextArea component

A JTextArea is a multi-line text area that displays plain text. It is lightweight component for working with text. The component does not handle scrolling. For this task, we use JScrollPane component.

package zetcode;

import java.awt.BorderLayout;
import java.awt.Dimension;

import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;

public class TextAreaExample extends JFrame {

    public TextAreaExample() {
        initUI();
    }

    public final void initUI() {

        JPanel panel = new JPanel();
        panel.setLayout(new BorderLayout());
        panel.setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));

        JScrollPane pane = new JScrollPane();
        JTextArea area = new JTextArea();

        area.setLineWrap(true);
        area.setWrapStyleWord(true);
        area.setBorder(BorderFactory.createEmptyBorder(8, 8, 8, 8));

        pane.getViewport().add(area);
        panel.add(pane);

        add(panel);

        setTitle("JTextArea");
        setSize(new Dimension(350, 300));
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
    }

    public static void main(String[] args) {

        SwingUtilities.invokeLater(new Runnable() {

            public void run() {
                TextAreaExample ex = new TextAreaExample();
                ex.setVisible(true);
            }
        });
    }
}

The example shows a simple JTextArea component.

JTextArea area = new JTextArea(); 

This is the constructor of the JTextArea component.

area.setLineWrap(true);

Make the lines wrapped, if they are too long to fit the width.

area.setWrapStyleWord(true);

Here we specify, how is line going to be wrapped. In our case, lines will be wrapped at word boundaries, whitespaces.

area.setBorder(BorderFactory.createEmptyBorder(8, 8, 8, 8));

We put some border around the text in the component.

pane.getViewport().add(area);

To make the text scrollable, we put the JTextArea component into the JScrollPane component.

Figure: JTextAra

JTextPane component

JTextPane component is a more advanced component for working with text. The component can do some complex formatting operations over the text. It can display also HTML documents.

package zetcode;

import java.awt.BorderLayout;
import java.awt.Dimension;

import java.io.IOException;

import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextPane;
import javax.swing.SwingUtilities;


public class TextPaneExample extends JFrame {

    public TextPaneExample() {

        initUI();
    }

    public final void initUI() {

        JPanel panel = new JPanel();
        panel.setLayout(new BorderLayout());
        panel.setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));

        JScrollPane pane = new JScrollPane();
        JTextPane textpane = new JTextPane();

        textpane.setContentType("text/html");
        textpane.setEditable(false);

        String cd = System.getProperty("user.dir") + "/";

        try {
            textpane.setPage("File:///" + cd + "test.html");
        } catch (IOException e) {
            System.out.println("Exception: " + e);
        }

        textpane.setBorder(BorderFactory.createEmptyBorder(8, 8, 8, 8));

        pane.getViewport().add(textpane);
        panel.add(pane);

        add(panel);

        setTitle("JTextPane");
        setSize(new Dimension(380, 320));
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
    }

    public static void main(String[] args) {

        SwingUtilities.invokeLater(new Runnable() {

            public void run() {
                TextPaneExample ex = new TextPaneExample();
                ex.setVisible(true);
            }
        });
    }
}

This is the HTML code, that we are loading into the JTextPane component. The component does not handle scrolling.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>A simple html document</title>
</head>
<body>

<h2>A simple html document</h2>


<p>
<b>JTextPane</b> can display html documents. 
</p>

<br>

<pre>
 JScrollPane pane = new JScrollPane();
 JTextPane textpane = new JTextPane(); 

 textpane.setContentType("text/html");
 textpane.setEditable(false);
</pre>

<br>
<small>The Java Swing tutorial, 2010</small>

</body>

</html>

In our example we show a JTextPane component and load a html document. Example shows formatting capabilities of the component.

JTextPane textpane = new JTextPane(); 

textpane.setContentType("text/html");
textpane.setEditable(false);

We create a JTextPane component, set the content of the component to be a HTML document and disable editing.

String cd = System.getProperty("user.dir") + "/";

Here we determine the current working directory of the user. The HTML document is located there.

try {
    textpane.setPage("File:///" + cd + "test.html");
} catch (IOException e) {
    System.out.println("Exception: " + e);
}

We load a HTML document into the pane.

Figure: JTextPane

In this chapter, we have continued covering basic Swing components.