SWING COMPONENTS

 The Swing components offer rich functionality and enable high-level customisation. The following components are described in this section.

• JLabel
• JTextField
• JButton
•  JToggleButton
• JCheckBox
• JRadioButton
• JTabbedPane
• JScrollPane
• JList
• JComboBox
• JTree
• JTable

JLabel

 JLabel is Swing’s easiest-to-use component.

JLabel can be used to display text and/or an icon.

 JLabel defines several constructors. Here are three of them: 

•  JLabel(Icon icon) 
•  JLabel(String str) 
•  JLabel(String str, Icon icon, int align)

 The align argument specifies the horizontal alignment of the text and/or icon within the label. It must be one of the following values: LEFT, RIGHT, CENTER, LEADING, or TRAILING.

The easiest way to obtain an icon is to use the ImageIcon class. An object of type ImageIcon can be passed as an argument to the Icon parameter of JLabel’s constructor.

Methods in JLabel

 The icon and text associated with the label can be obtained by the following methods: 

 Icon getIcon( ) 

 String getText( )

The icon and text associated with a label can be set by these methods: 

 void setIcon(Icon icon)

 void setText(String str)

Program using JLabel

import java.awt.*;

import javax.swing.*;

public class MyFrame extends JFrame

{

JLabel l;

MyFrame()

{

setSize(500, 300);

setTitle("My Application");

setLayout(new FlowLayout());

l = new JLabel("This is a label!");

add(l);

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

public static void main(String[] args)

{

MyFrame mf = new MyFrame();

}

}

JTextField

 JTextField is the simplest and most widely used Swing text component. JTextField allows you to edit one line of text. It is derived from JTextComponent. Three of JTextField’s constructors are shown here: 

•  JTextField(int cols)
•  JTextField(String str, int cols) 
•  JTextField(String str) 

 Here, str is the string to be initially presented, and cols is the number of columns in the text field. 

If no string is specified, the text field is initially empty.

Events handled in JTextField

ActionEvent - when the user presses the Enter key

 CaretEvent - each time the cursor changes position

Methods in JTextField

setText() - to display text

getText() - to retrieve text from the text field

Program using JTextField

 import java.awt.*;

import javax.swing.*;

public class MyFrame extends JFrame

{

JTextField jtf;

MyFrame()

{

setSize(500, 300);

setTitle("My Application");

setLayout(new FlowLayout());

jtf = new JTextField(20);

add(jtf);

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

public static void main(String[] args)

{

MyFrame mf = new MyFrame();

}

}

Swing Buttons

Swing defines four types of buttons: JButton, JToggleButton, JCheckBox, and JRadioButton.

A button generates an action event when it is pressed. 

JButton

The JButton class provides the functionality of a push button. Three of its constructors are shown here: 

•  JButton(Icon icon)
•  JButton(String str) 
•  JButton(String str, Icon icon) 

 When the button is pressed, an ActionEvent is generated.

getActionCommand()  - used to identify the button pressed when two or more buttons are present.

Program using JButton

import java.awt.*;

import javax.swing.*;

public class MyFrame extends JFrame

{

JButton b;

MyFrame()

{

setSize(500, 300);

setTitle("My Application");

setLayout(new FlowLayout());

b = new JButton("Click Me");

add(b);

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

public static void main(String[] args)

{

MyFrame mf = new MyFrame();

}

}

JToggleButton

 A toggle button looks just like a push button, but it acts differently because it has two states: pushed and released. JToggleButton defines several constructors. The most commonly used one is:

 JToggleButton(String str)

JToggleButton generates an action event each time it is pressed. 

JToggleButton also generates an item event. 

•  When a JToggleButton is pressed, it is selected. When it is popped out, it is deselected.
• To handle ItemEvent, the ItemListener interface is implemented. This interface provides itemStateChanged() method. Inside itemStateChanged( ), 

getItem( ) - method can be used to identify the item selected.

isSelected() - used to check whether an item is selected or not.

Program using JToggleButton

import java.awt.*;

import javax.swing.*;

public class MyFrame extends JFrame

{

JToggleButton b;

MyFrame()

{

setSize(500, 300);

setTitle("My Application");

setLayout(new FlowLayout());

b = new JToggleButton("Click Me");

add(b);

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

public static void main(String[] args)

{

MyFrame mf = new MyFrame();

}

}

 Check Boxes

The JCheckBox class provides the functionality of a check box. JCheckBox defines several constructors. The one used here is

• JCheckBox(String str) 

When the user selects or deselects a check box, an ItemEvent is generated.

A call to isSelected( ) determines if the box was selected or cleared. The getText( ) method gets the text for that check box.

Program using JCheckBox

import java.awt.*;

import javax.swing.*;

public class MyFrame extends JFrame

{

JCheckBox c1;

JCheckBox c2;

JCheckBox c3;

MyFrame()

{

setSize(500, 300);

setTitle("My Application");

setLayout(new FlowLayout());

c1 = new JCheckBox("C");

c2 = new JCheckBox("C++");

c3 = new JCheckBox("Java");

add(c1);

add(c2);

add(c3);

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

public static void main(String[] args)

{

MyFrame mf = new MyFrame();

}

}

Radio Buttons

 Radio buttons are a group of mutually exclusive buttons, where only one button can be selected at any time. They are supported by the JRadioButton class, which extends JToggleButton. JRadioButton provides several constructors.

 JRadioButton(String str)

 In order for their mutually exclusive nature to be activated, radio buttons must be configured into a group. Only one of the buttons in the group can be selected at any time. A button group is created by the ButtonGroup class.   Elements are then added to the button group via the following method: 

 void add(AbstractButton ab)

Methods

getActionCommand() - returns the label of the radio button

isSelected() - used to check whether a radio button is selected

getSource() - used to identify the radio button pressed

Program using JRadioButton

import java.awt.*;

import javax.swing.*;

public class MyFrame extends JFrame

{

JRadioButton r1;

JRadioButton r2;

ButtonGroup bg;

MyFrame()

{

setSize(500, 300);

setTitle("My Application");

setLayout(new FlowLayout());

r1 = new JRadioButton("Male");

r2 = new JRadioButton("Female");

add(r1);

add(r2);

bg = new ButtonGroup();

bg.add(r1);

bg.add(r2);

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

public static void main(String[] args)

{

MyFrame mf = new MyFrame();

}

}

 JTabbedPane

Tabbed panes are very common in the modern GUI.  It manages a set of components by linking them with tabs. Selecting a tab causes the component associated with that tab to come to the forefront. JTabbedPane defines three constructors. 

JTabbedPane()

JTabbedPane(int tabPlacement)

After creating a TabbedPane object, tabs are added using the following method:

 void addTab(String name, Component comp)

  The general procedure to use a tabbed pane is outlined here: 

1.  Create an instance of JTabbedPane. 
2.  Add each tab by calling addTab( ). 
3.  Add the tabbed pane to the content pane

Program Using JTabbedPane

import java.awt.*;

import javax.swing.*;
public class MyFrame extends JFrame
{
JCheckBox c1;
JCheckBox c2;
JCheckBox c3;
JRadioButton r1;
JRadioButton r2;
ButtonGroup bg;
JLabel l;
JTextField jtf;
JPanel langs;
JPanel gender;
JPanel name;
JTabbedPane jtp;
MyFrame()
{
setSize(500, 300);
setTitle("My Application");
setLayout(new FlowLayout());
c1 = new JCheckBox("C");
c2 = new JCheckBox("C++");
c3 = new JCheckBox("Java");
langs = new JPanel();
langs.add(c1);
langs.add(c2);
langs.add(c3);
r1 = new JRadioButton("Male");
r2 = new JRadioButton("Female");
bg = new ButtonGroup();
bg.add(r1);
bg.add(r2);
gender = new JPanel();
gender.add(r1);
gender.add(r2);
l = new JLabel("Enter Name: ");
jtf = new JTextField(20);
name = new JPanel();
name.add(l);
name.add(jtf);
jtp = new JTabbedPane();
jtp.addTab("Languages", langs);
jtp.addTab("Gender", gender);
jtp.addTab("Name", name);
add(jtp);
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public static void main(String[] args)
{
MyFrame mf = new MyFrame();
}
}

 JScrollPane

 JScrollPane is a lightweight container that automatically handles the scrolling of another component. The component being scrolled can be either an individual component or a group of components.  In either case, if the object being scrolled is larger than the viewable area, horizontal and/or vertical scroll bars are automatically provided.

The viewable area of a scroll pane is called the viewport. It is a window in which the component being scrolled is displayed. The scroll bars scroll the component through the viewport.  A JScrollPane will dynamically add or remove a scroll bar as needed.  JScrollPane defines several constructors. The simplest one is hown here: 

 JScrollPane(Component comp)

 Here are the steps to follow to use a scroll pane: 

1.  Create the component to be scrolled. 
2.  Create an instance of JScrollPane, passing to it the object to scroll. 
3.  Add the scroll pane to the content pane

Program using JScrollPane

 import javax.swing.*;

public class JScrollPaneExample
{
    public static void main(String[] args)
    {
        // Create a JFrame
        JFrame frame = new JFrame("JScrollPane Example");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(400, 300);
 
        // Create a JTextArea
        JTextArea textArea = new JTextArea(10, 30);
        textArea.setText("This is a sample text.
                          \nYou can add more lines to see the scroll effect.
                          \nKeep typing to test scrolling!");
 
        // Wrap the JTextArea inside a JScrollPane
        JScrollPane scrollPane = new JScrollPane(textArea);
 
        // Add the JScrollPane to the frame
        frame.add(scrollPane);
         // Make the frame visible
        frame.setVisible(true);
    }
}

 JList

 In Swing, the basic list class is called JList. It supports the selection of one or more items from a list..

 JList provides several constructors. The one used here is 

•  JList(E[ ] items)

 JList is based on two models. The first is ListModel. This interface defines how access to the list data is achieved. The second model is the ListSelectionModel interface, which defines methods that determine what list item or items are selected.

 A JList generates a ListSelectionEvent when the user makes or changes a selection.  It is handled by implementing ListSelectionListener. This listener specifies only one method, called valueChanged( ), 

By default, a JList allows the user to select multiple ranges of items within the list. The method

void setSelectionMode(int mode)

is used to change the selection mode. It must be one of these values defined by ListSelectionModel: SINGLE_SELECTION 

 SINGLE_INTERVAL_SELECTION 

 MULTIPLE_INTERVAL_SELECTION

Methods to get the selected items

 int getSelectedIndex( ) 

 Indexing begins at zero. So, if the first item is selected, this method will return 0. If no item is selected, –1 is returned.

 getSelectedValue( ) 

 It returns a reference to the first selected value. If no value has been selected, it returns null.

Program using JList

import java.awt.*;

import javax.swing.*;
public class MyFrame extends JFrame
{
JList<String> jl;
JScrollPane jsp;
MyFrame()
{
setSize(500, 300);
setTitle("My Application");
setLayout(new FlowLayout());
String[] branches = {"CSE", "ECE", "EEE", "IT", "MECH", "CIV"};
jl = new JList<String>(branches);
jsp = new JScrollPane(jl);
jsp.setPreferredSize(new Dimension(120, 80));
add(jsp);
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public static void main(String[] args)
{
MyFrame mf = new MyFrame();
}
}

 JComboBox

A combo box (a combination of a text field and a drop-down list) 

A combo box displays one entry, but it will also display a drop-down list that allows a user to select a different entry. 

 The JComboBox constructor used by the example is shown here: 

 JComboBox(E[ ] items)

 Items can be dynamically added to the list of choices via the addItem( ) method, shown here: 

 void addItem(E obj)

JComboBox generates an 

action event when the user selects an item from the list. 

item event  - when the state of selection changes, which occurs when an item is selected or deselected.

getSelectedItem( ) -  to obtain the item selected in the list 

Program using JComboBox

import java.awt.*;

import javax.swing.*;

public class MyFrame extends JFrame

{

JComboBox<String> jc;

MyFrame()

{

setSize(500, 300);

setTitle("My Application");

setLayout(new FlowLayout());

String[] branches = {"CSE", "ECE", "EEE", "IT", "MECH", "CIV"};

jc = new JComboBox<String>(branches);

add(jc);

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

public static void main(String[] args)

{

MyFrame mf = new MyFrame();

}

}

Trees

 A tree is a component that presents a hierarchical view of data. Trees are implemented in Swing by the JTree class. A sampling of its constructors is shown here:

•  JTree(Object[ ] obj) 
•  JTree(Vector v) 
•  JTree(TreeNode tn)

Although JTree is packaged in javax.swing, its support classes and interfaces are packaged in javax.swing.tree.

 JTree relies on two models: TreeModel and TreeSelectionModel.

Events generated

TreeExpansionEvent events occur when a node is expanded or collapsed. 

TreeSelectionEvent is generated when the user selects or deselects a node within the tree.

TreeModelEvent is fired when the data or structure of the tree changes. 

The listeners for these events are TreeExpansionListener, TreeSelectionListener, and TreeModelListener, respectively. The tree event classes and listener interfaces are packaged in javax.swing.event.

 Here are the steps to follow to use a tree:

1.  Create an instance of JTree. 
2.  Create a JScrollPane and specify the tree as the object to be scrolled.
3.  Add the scroll pane to the content pane. 

Program using JTree

import javax.swing.*;

import javax.swing.tree.DefaultMutableTreeNode;

public class SimpleJTreeExample {

    public static void main(String[] args) {

        // Create the root node

        DefaultMutableTreeNode root = new DefaultMutableTreeNode("Root");

        // Add child nodes

        DefaultMutableTreeNode child1 = new DefaultMutableTreeNode("Child 1");

        DefaultMutableTreeNode child2 = new DefaultMutableTreeNode("Child 2");

        root.add(child1);

        root.add(child2);

        // Add sub-child nodes

        child1.add(new DefaultMutableTreeNode("Sub-child 1.1"));

        child1.add(new DefaultMutableTreeNode("Sub-child 1.2"));

        child2.add(new DefaultMutableTreeNode("Sub-child 2.1"));

        // Create the JTree

        JTree tree = new JTree(root);

        // Add the tree to a scroll pane

        JScrollPane treeView = new JScrollPane(tree);

        // Create a JFrame to display the tree

        JFrame frame = new JFrame("Simple JTree Example");

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        frame.add(treeView);

        frame.setSize(300, 300);

        frame.setVisible(true);

    }

}

 JTable

 JTable is a component that displays rows and columns of data. It is also possible to select a row, column, or cell within the table, and to change the data within a cell.  JTable has many classes and interfaces associated with it. These are packaged in javax.swing.table. 

 JTable supplies several constructors. The one used here is 

•  JTable(Object[ ][ ] data, Object[ ] colHeads). 

 Here, data is a two-dimensional array of the information to be presented, and colHeads is a one-dimensional array with the column headings.

 JTable relies on three models.

TableModel - defines those things related to displaying data in a two-dimensional format

TableColumnModel -  defines a table in terms of columns

ListSelectionModel - determines how items are selected in the table

 A JTable can generate several different events.

ListSelectionEvent is generated when the user selects something in the table

TableModelEvent is fired when that table’s data changes in some way

 Here are the steps required to set up a simple JTable that can be used to display data: 

 Create an instance of JTable. 

 Create a JScrollPane object, specifying the table as the object to scroll. 

 Add the scroll pane to the content pane.

Program using JTable

import java.awt.*;

import javax.swing.*;

public class MyFrame extends JFrame

{

JTable jt;

JScrollPane jsp;

MyFrame()

{

setSize(500, 300);

setTitle("My Application");

setLayout(new FlowLayout());

String[] colHeads = {"Student", "JP", "FLAT", "CO"};

String[][] data = { {"Ramesh", "77", "80", "75"},

{"Suresh", "89", "86", "83"},

{"Mahesh", "74", "80", "75"},

{"Dinesh", "78", "80", "75"},

{"Gireesh", "89", "86", "83"},

{"Paramesh", "77", "84", "72"} };

jt = new JTable(data, colHeads);

jsp = new JScrollPane(jt);

jsp.setPreferredSize(new Dimension(450, 100));

add(jsp);

setVisible(true);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

}

public static void main(String[] args)

{

MyFrame mf = new MyFrame();

}

}