Friday, May 27, 2011

Using Colors

Now that we know how to create various 2D shapes, the next step would be to use colors in our UI components. Not everything looks fine in black and white. Colors bring some radiance and class to the look and feel of a UI component. In this chapter, we are going to learn how to do just that.

So, lets get started!!!

Using Colors:

The setPaint method of the Graphics2D class lets you select a color that will be used for all subsequent drawing operations on the graphics context. For example:

g2.setPaint(Color.RED);
g2.drawString("Caution!", 100, 100);

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

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

To draw in multiple colors, you select a color, draw or fill, then select another color, and draw or fill again.

You define colors with the Color class. The java.awt.Color class offers predefined constants for the following 13 standard colors:

BLACK, BLUE, CYAN, DARK_GRAY, GRAY, GREEN, LIGHT_GRAY, MAGENTA, ORANGE, PINK, RED, WHITE, YELLOW

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 and then invoke the Color constructor like below:

Color(int redness, int greenness, int blueness)

Example:
g2.setPaint(new Color(0, 128, 128));
g2.drawString("Welcome!", 75, 125);

To set the background color, you use the setBackground method of the Component class, an ancestor of JComponent.

MyComponent p = new MyComponent();
p.setBackground(Color.MAGENTA);

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

Trivia:
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,
p.setBackground(SystemColor.window)

sets the background color of the component to the default used by all windows on the user’s desktop.

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.

Let us now take a look at all the possible color options available in the System Color class and their usage.
Name Usage/Purpose
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

Prev: Creating a 2D Shape

Next: Using Special Fonts for Text

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