Java Swing: JComponent, JLayeredPane & JDEsktopPane

Java JComponent

The JComponent class is the base class of all Swing components except top-level containers. Swing components whose names begin with "J" are descendants of the JComponent class. For example, JButton, JScrollPane, JPanel, JTable etc. But, JFrame and JDialog don't inherit JComponent class because they are the child of top-level containers.

The JComponent class extends the Container class which itself extends Component. The Container class has support for adding components to the container.

Fields

Modifier and Type	Field	Description
protected AccessibleContext	accessibleContext	The AccessibleContext associated with this JComponent.
protectedEventListenerList	listenerList	A list of event listeners for this component.
static String	TOOL_TIP_TEXT_KEY	The comment to display when the cursor is over the component, also known as a "value tip", "flyover help", or "flyover label"
protected ComponentUI	ui	The look and feel delegate for this component.
static int	UNDEFINED_CONDITION	It is a constant used by some of the APIs to mean that no condition is defined.
static int	WHEN_ANCESTOR_OF_FOCUSED_COMPONENT	It is a constant used for registerKeyboardAction that means that the command should be invoked when the receiving component is an ancestor of the focused component or is itself the focused component.
static int	WHEN_FOCUSED	It is a constant used for registerKeyboardAction that means that the command should be invoked when the component has the focus.
static int	WHEN_IN_FOCUSED_WINDOW	Constant used for registerKeyboardAction that means that the command should be invoked when the receiving component is in the window that has the focus or is itself the focused component.

Constructor

Constructor	Description
JComponent()	Default JComponent constructor.

Useful Methods

Modifier and Type	Method	Description
void	setActionMap(ActionMap am)	It sets the ActionMap to am.
void	setBackground(Color bg)	It sets the background color of this component.
void	setFont(Font font)	It sets the font for this component.
void	setMaximumSize(Dimension maximumSize)	It sets the maximum size of this component to a constant value.
void	setMinimumSize(Dimension minimumSize)	It sets the minimum size of this component to a constant value.
protected void	setUI(ComponentUI newUI)	It sets the look and feel delegate for this component.
void	setVisible(boolean aFlag)	It makes the component visible or invisible.
void	setForeground(Color fg)	It sets the foreground color of this component.
String	getToolTipText(MouseEvent event)	It returns the string to be used as the tooltip for event.
Container	getTopLevelAncestor()	It returns the top-level ancestor of this component (either the containing Window or Applet), or null if this component has not been added to any container.
TransferHandler	getTransferHandler()	It gets the transferHandler property.

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Java JComponent Example

1. import java.awt.Color;  
2. import java.awt.Graphics;  
3. import javax.swing.JComponent;  
4. import javax.swing.JFrame;  
5. class MyJComponent extends JComponent {  
6.       public void paint(Graphics g) {  
7.         g.setColor(Color.green);  
8.         g.fillRect(30, 30, 100, 100);  
9.       }  
10. }  
11. public class JComponentExample {  
12.       public static void main(String[] arguments) {  
13.         MyJComponent com = new MyJComponent();  
14.         // create a basic JFrame  
15.         JFrame.setDefaultLookAndFeelDecorated(true);  
16.         JFrame frame = new JFrame("JComponent Example");  
17.         frame.setSize(300,200);  
18.         frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
19.         // add the JComponent to main frame  
20.         frame.add(com);  
21.         frame.setVisible(true);  
22.       }  
23. }  

Output:

Java JLayeredPane

The JLayeredPane class is used to add depth to swing container. It is used to provide a third dimension for positioning component and divide the depth-range into several different layers.

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JLayeredPane class declaration

1. public class JLayeredPane extends JComponent implements Accessible  

Commonly used Constructors:

Constructor	Description
JLayeredPane	It is used to create a new JLayeredPane

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Commonly used Methods:

Method	Description
int getIndexOf(Component c)	It is used to return the index of the specified Component.
int getLayer(Component c)	It is used to return the layer attribute for the specified Component.
int getPosition(Component c)	It is used to return the relative position of the component within its layer.

Java JLayeredPane Example

1. import javax.swing.*;  
2. import java.awt.*;  
3. public class LayeredPaneExample extends JFrame {  
4.   public LayeredPaneExample() {  
5.     super("LayeredPane Example");  
6.     setSize(200, 200);  
7.     JLayeredPane pane = getLayeredPane();  
8.     //creating buttons  
9.     JButton top = new JButton();  
10.     top.setBackground(Color.white);  
11.     top.setBounds(20, 20, 50, 50);  
12.     JButton middle = new JButton();  
13.     middle.setBackground(Color.red);  
14.     middle.setBounds(40, 40, 50, 50);  
15.     JButton bottom = new JButton();  
16.     bottom.setBackground(Color.cyan);  
17.     bottom.setBounds(60, 60, 50, 50);  
18.     //adding buttons on pane  
19.     pane.add(bottom, new Integer(1));  
20.     pane.add(middle, new Integer(2));  
21.     pane.add(top, new Integer(3));  
22.   }  
23.   public static void main(String[] args) {  
24.       LayeredPaneExample panel = new  LayeredPaneExample();  
25.       panel.setVisible(true);  
26.   }  
27. }  

Output:

Java JLayeredPane Example

1. import javax.swing.*;  
2. import java.awt.*;  
3. public class LayeredPaneExample extends JFrame {  
4.   public LayeredPaneExample() {  
5.     super("LayeredPane Example");  
6.     setSize(200, 200);  
7.     JLayeredPane pane = getLayeredPane();  
8.     //creating buttons  
9.     JButton top = new JButton();  
10.     top.setBackground(Color.white);  
11.     top.setBounds(20, 20, 50, 50);  
12.     JButton middle = new JButton();  
13.     middle.setBackground(Color.red);  
14.     middle.setBounds(40, 40, 50, 50);  
15.     JButton bottom = new JButton();  
16.     bottom.setBackground(Color.cyan);  
17.     bottom.setBounds(60, 60, 50, 50);  
18.     //adding buttons on pane  
19.     pane.add(bottom, new Integer(1));  
20.     pane.add(middle, new Integer(2));  
21.     pane.add(top, new Integer(3));  
22.   }  
23.   public static void main(String[] args) {  
24.       LayeredPaneExample panel = new  LayeredPaneExample();  
25.       panel.setVisible(true);  
26.   }  
27. }  

Output:

Java JDesktopPane

The JDesktopPane class, can be used to create "multi-document" applications. A multi-document application can have many windows included in it. We do it by making the contentPane in the main window as an instance of the JDesktopPane class or a subclass. Internal windows add instances of JInternalFrame to the JdesktopPane instance. The internal windows are the instances of JInternalFrame or its subclasses.

Fields

Modifier and Type	Field	Description
static int	LIVE_DRAG_MODE	It indicates that the entire contents of the item being dragged should appear inside the desktop pane.
static int	OUTLINE_DRAG_MODE	It indicates that an outline only of the item being dragged should appear inside the desktop pane.

Constructor

Constructor	Description
JDesktopPane()	Creates a new JDesktopPane.

Java JDesktopPane Example

1. import java.awt.BorderLayout;  
2. import java.awt.Container;  
3. import javax.swing.JDesktopPane;  
4. import javax.swing.JFrame;  
5. import javax.swing.JInternalFrame;  
6. import javax.swing.JLabel;  
7. public class JDPaneDemo extends JFrame  
8. {  
9.   public JDPaneDemo()   
10.   {  
11.     CustomDesktopPane desktopPane = new CustomDesktopPane();  
12.     Container contentPane = getContentPane();  
13.     contentPane.add(desktopPane, BorderLayout.CENTER);  
14.     desktopPane.display(desktopPane);  
15.   
16.     setTitle("JDesktopPane Example");  
17.     setSize(300,350);  
18.     setVisible(true);  
19.   }  
20.   public static void  main(String args[])  
21.   {  
22.     new JDPaneDemo();  
23.   }  
24. }  
25. class CustomDesktopPane extends JDesktopPane  
26. {  
27.   int numFrames = 3,  x = 30, y = 30;  
28.   public void display(CustomDesktopPane dp)   
29.   {  
30.     for(int  i = 0; i < numFrames ; ++i )   
31.     {  
32.       JInternalFrame jframe = new JInternalFrame("Internal Frame " + i ,  true, true, true, true);  
33.   
34.       jframe.setBounds(x, y, 250, 85);  
35.      Container c1 = jframe.getContentPane( ) ;  
36.      c1.add(new JLabel("I love my country"));  
37.      dp.add( jframe );  
38.      jframe.setVisible(true);         
39.      y += 85;  
40.     }  
41.   }  
42. }  

Output:

Anurag Rana Educator CSE/IT