15.2. Buttons

[Page 452 ( continued )]

13.14. (Optional) Case Study: The ImageViewer Class

Displaying an image is a common task in Java programming. This case study develops a reusable component named ImageViewer that displays an image on a panel. The class contains the properties image , stretched , xCoordinate , and yCoordinate , with associated accessor and mutator methods , as shown in Figure 13.24.

Figure 13.24. The ImageViewer class displays an image on a panel.

(This item is displayed on page 453 in the print version)

You can use images in Swing components like JLabel and JButton , but these images are not stretchable. The image in an ImageViewer can be stretched.

Let us write a test program in Listing 13.14 that displays six images using the ImageViewer class. Figure 13.25 shows a sample run of the program.

Figure 13.25. Six images are displayed in six ImageViewer components.

(This item is displayed on page 453 in the print version)

---

[Page 453]

Listing 13.14. SixFlags.java

 1   import   javax.swing.*; 2   import   java.awt.*; 3 4   public class   SixFlags   extends   JFrame { 5   public   SixFlags() { 6 Image image1 =   new   ImageIcon(   "image/us.gif"   ).getImage(); 7 Image image2 =   new   ImageIcon(   "image/ca.gif"   ).getImage(); 8 Image image3 =   new   ImageIcon(   "image/india.gif"   ).getImage(); 9 Image image4 =   new   ImageIcon(   "image/uk.gif"   ).getImage(); 10 Image image5 =   new   ImageIcon(   "image/china.gif"   ).getImage(); 11 Image image6 =   new   ImageIcon(   "image/norway.gif"   ).getImage(); 12 13 setLayout(   new   GridLayout(   2   ,     ,   5   ,   5   )); 14 add(   new   ImageViewer(image1)); 15 add(   new   ImageViewer(image2)); 16 add(   new   ImageViewer(image3)); 17 add(   new   ImageViewer(image4)); 18 add(   new   ImageViewer(image5)); 19 add(   new   ImageViewer(image6)); 20 } 21 22   public static void   main(String[] args) { 23 SixFlags frame =   new   SixFlags(); 24 frame.setTitle(   "SixFlags"   ); 25 frame.setLocationRelativeTo(   null   );  // Center the frame  26 frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 27 frame.setSize(   400   ,   320   ); 28 frame.setVisible(   true   ); 29 } 30 } 

---

[Page 454]

The ImageViewer class is implemented in Listing 13.15. ( Note: You may skip the implementation. ) The accessor and mutator methods for the properties image , stretched , xCoordinate , and yCoordinate are easy to implement. The paintComponent method (lines 26 “35) displays the image on the panel. Line 29 ensures that the image is not null before displaying it. Line 30 checks whether the image is stretched or not.

Listing 13.15. ImageViewer.java

(This item is displayed on pages 454 - 455 in the print version)

 1   import   java.awt.*; 2   import   javax.swing.*; 3 4    public class   ImageViewer   extends   JPanel  { 5  /** Hold value of property image. */  6   private   java.awt.Image image; 7 8  /** Hold value of property stretched. */  9   private boolean   stretched =   true   ; 10 11  /** Hold value of property xCoordinate. */  12   private int   xCoordinate; 13 14  /** Hold value of property yCoordinate. */  15   private int   yCoordinate; 16 17  /** Construct an empty image viewer */  18   public   ImageViewer() { 19 } 20 21  /** Construct an image viewer for a specified Image object */  22   public   ImageViewer(Image image) { 23   this   .image = image; 24 } 25 26    protected void   paintComponent(Graphics g)  { 27   super   .paintComponent(g); 28 29    if   (image !=   null   )  30   if   (  isStretched()  ) 31 g.drawImage(image, xCoordinate, yCoordinate, 32 getSize().width, getSize().height,   this   ); 33   else   34 g.drawImage(image, xCoordinate, yCoordinate,   this   ); 35 } 36 37  /** Return value of property image */  38   public   java.awt.Image getImage() { 39   return   image; 40 } 41 42  /** Set a new value for property image */  43   public void   setImage(java.awt.Image image) { 44   this   .image = image; 45 repaint(); 46 } 47 48  /** Return value of property stretched */  49   public boolean   isStretched() { 50   return   stretched; 51 } 52 

---

[Page 455]

 53  /** Set a new value for property stretched */  54   public void   setStretched(   boolean   stretched) { 55   this   .stretched = stretched; 56 repaint(); 57 } 58 59  /** Return value of property xCoordinate */  60   public int   getXCoordinate() { 61   return   xCoordinate; 62 } 63 64  /** Set a new value for property xCoordinate */  65   public void   setXCoordinate(   int   xCoordinate) { 66   this   .xCoordinate = xCoordinate; 67 repaint(); 68 } 69 70  /** Return value of property yCoordinate */  71   public int   getYCoordinate() { 72   return   yCoordinate; 73 } 74 75  /** Set a new value for property yCoordinate */  76   public void   setYCoordinate(   int   yCoordinate) { 77   this   .yCoordinate = yCoordinate; 78 repaint(); 79 } 80 }