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Screenshot Core Java 2: Volume I - Fundamentals

Table of Contents
 7.  Graphics Programming


Colors

The setPaint method of the Graphics2D class lets you select a color that is used for all subsequent drawing operations on the graphics context or component. To draw in multiple colors, you select a color, draw, then select another color, and draw again. You define colors with the Color class. The java.awt.Color class offers predefined constants for the 13 standard colors listed in Table 7-1.

Table 7-1. Standard colors

BLACK

GREEN

RED

BLUE

LIGHT_GRAY

WHITE

CYAN

MAGENTA

YELLOW

DARK_GRAY

ORANGE

 

GRAY

PINK

 
For example,
g2.setPaint(Color.RED);
g2.drawString("Warning!", 100, 100);


Java graphics notes_icon.gif

Before SDK 1.4, color constant names were lowercase such as Color.red. This is odd since the standard coding convention is to write constants in uppercase. Starting with SDK 1.4, you can write the standard color names in uppercase or, for backward compatibility, in lowercase. We use the uppercase constants in our programs. If you use an older version of the SDK, you need to change the color names to lowercase.

You can specify a custom color by creating a Color object by its red, green, and blue components. Using a scale of 0–255 (that is, one byte) for the redness, blueness, and greenness, call the Color constructor like this:
Color(int redness, int greenness, int blueness)


Here is an example of setting a custom color:

g.setPaint(new Color(0, 128, 128)); // a dull blue-green g.drawString("Welcome!", 75, 125);


Java graphics notes_icon.gif

In addition to solid colors, you can select more complex "paint" settings, such as varying hues or images. See the Advanced AWT chapter in Volume 2 for more details. If you use a Graphics object instead of a Graphics2D object, you need to use the setColor method to set colors.

To set the background color, you use the setBackground method of the Component class, an ancestor of JPanel. In fact, you should set the background before displaying the frame for the first time.
MyPanel p = new MyPanel();
p.setBackground(Color.WHITE);
contentPane.add(p);


There is also a setForeground method. It specifies the default color that is used for drawing on the component.

Java graphics exclamatory_icon.gif

The brighter() and darker() methods of the Color class produce, as their names suggest, either brighter or darker versions of the current color. Using the brighter method is also a good way to highlight an item. Actually, brighter() is just a little bit brighter. To make a color really stand out, apply it three times: c.brighter().brighter().brighter().

Java gives you predefined names for many more colors in its SystemColor class. The constants in this class encapsulate the colors used for various elements of the user's system. For example,
frame.setBackground(SystemColor.window)


sets the background color of the frame to the default used by all windows on the user's desktop. (The background is filled in whenever the window is repainted.) Using the colors in the SystemColor class is particularly useful when you want to draw user interface elements so that the colors match those already found on the user's desktop. Table 7-2 lists the system color names and their meanings.

java.awt.Color 1.0

Java graphics api_icon.gif
  • Color(int r, int g, int b)

    creates a color object.

    Parameters:

    r

    The red value (0–255)

     

    g

    The green value (0–255)

     

    b

    The blue value (0–255)

java.awt.Graphics 1.0

Java graphics api_icon.gif
  • void setColor(Color c)

    changes the current color. All subsequent graphics operations will use the new color.

    Parameters:

    c

    The new color

java.awt.Graphics2D 1.2

Java graphics api_icon.gif
  • void setPaint(Paint p)

    Sets the paint attribute of this graphics context. The Color class implements the Paint interface. Therefore, you can use this method to set the paint attribute to a solid color.

java.awt.Component 1.0

Java graphics api_icon.gif
  • void setBackground(Color c)

    sets the background color.

    Parameters:

    c

    The new background color

  • void setForeground(Color c)

    sets the foreground color.

    Parameters:

    c

    The new foreground color

Filling Shapes

You can fill the interiors of closed shapes (such as rectangles or ellipses) with a color (or, more generally, the current paint setting). Simply call fill instead of draw:

Rectangle2D rect = . . .;
g2.setPaint(Color.RED);
g2.fill(rect); // fills rect with red color


Table 7-2. System colors

desktop

Background color of desktop

activeCaption

Background color for captions

activeCaptionText

Text color for captions

activeCaptionBorder

Border color for caption text

inactiveCaption

Background color for inactive captions

inactiveCaptionText

Text color for inactive captions

inactiveCaptionBorder

Border color for inactive captions

window

Background for windows

windowBorder

Color of window border frame

windowText

Text color inside windows

menu

Background for menus

menuText

Text color for menus

text

Background color for text

textText

Text color for text

textInactiveText

Text color for inactive controls

textHighlight

Background color for highlighted text

textHighlightText

Text color for highlighted text

control

Background color for controls

controlText

Text color for controls

controlLtHighlight

Light highlight color for controls

controlHighlight

Highlight color for controls

controlShadow

Shadow color for controls

controlDkShadow

Dark shadow color for controls

scrollbar

Background color for scrollbars

info

Background color for spot-help text

infoText

Text color for spot-help text

The program in Example 7-5 fills a rectangle in red, then an ellipse with the same boundary in a dull green (see Screenshot-12).
Example 7-5 FillTest.java
 1. import java.awt.*;
 2. import java.awt.geom.*;
 3. import javax.swing.*;
 4.
 5. public class FillTest
 6. {
 7. public static void main(String[] args)
 8. {
 9. FillFrame frame = new FillFrame();
10. frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
11. frame.show();
12. }
13. }
14.
15. /**
16. A frame that contains a panel with drawings
17. */
18. class FillFrame extends JFrame
19. {
20. public FillFrame()
21. {
22. setTitle("FillTest");
23. setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
24.
25. // add panel to frame
26.
27. FillPanel panel = new FillPanel();
28. Container contentPane = getContentPane();
29. contentPane.add(panel);
30. }
31.
32. public static final int DEFAULT_WIDTH = 400;
33. public static final int DEFAULT_HEIGHT = 400;
34. }
35.
36. /**
37. A panel that displays filled rectangles and ellipses
38. */
39. class FillPanel extends JPanel
40. {
41. public void paintComponent(Graphics g)
42. {
43. super.paintComponent(g);
44. Graphics2D g2 = (Graphics2D)g;
45.
46. // draw a rectangle
47.
48. double leftX = 100;
49. double topY = 100;
50. double width = 200;
51. double height = 150;
52.
53. Rectangle2D rect = new Rectangle2D.Double(leftX, topY,
54. width, height);
55. g2.setPaint(Color.RED);
56. g2.fill(rect);
57.
58. // draw the enclosed ellipse
59.
60. Ellipse2D ellipse = new Ellipse2D.Double();
61. ellipse.setFrame(rect);
62. g2.setPaint(new Color(0, 128, 128)); // a dull blue-green
63. g2.fill(ellipse);
64. }
65. }


Screenshot-12. Filled rectangles and ellipses

Java graphics 07fig12.gif


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