Chapter 3 Fonts and Colors

 

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(((red & 0xFF) << 16 ) | ((green & 0xFF) << 8) | ((blue & 0xFF) << 0))

For example, consider a screen that uses four colors: one each for the foreground, the background, inactive components, and highlighted text. In the system properties file, you allow users to select colors by setting the following properties:

One particular user set two:

myPackage.myClass.foreground=0xff00ff        #magenta
myPackage.myClass.background=0xe0e0e0        #light gray

These lines tell the program to use magenta as the foreground color and light gray for the background. The program will use its default colors for inactive components and highlighted text.

public static Color getColor (String name)

The getColor() method gets the color specified by the system property name. If name is not a valid system property, getColor() returns null. If the property value does not convert to an integer, getColor() returns null.

For the properties listed above, if you call getColor() with name set to the property myPackage.myClass.foreground, it returns a magenta Color object. If called with name set to myPackage.myClass.inactive, getColor() returns null.

public static Color getColor (String name, Color defaultColor)

The getColor() method gets the color specified by the system property name. This version of the getColor() method returns defaultColor if name is not a valid system property or the property's value does not convert to an integer.

For the previous example, if getColor() is called with name set to myPackage.myClass.inactive, the getColor() method returns the value of defaultColor. This allows you to provide defaults for properties the user doesn't wish to set explicitly.

public static Color getColor (String name, int defaultColor)

This getColor() method gets the color specified by the system property name. This version of the getColor() method returns defaultColor if name is not a valid system property or the property's value does not convert to an integer. The default color is specified as an integer in which bits 16-23 represent the red component, 8-15 represent the green component, and 0-7 represent the blue component. Bits 24-31 are ignored. If the property value does not convert to an integer, defaultColor is returned.

public static Color decode (String name)

The decode() method provides an explicit means to decipher color property settings, regardless of where the setting comes from. (The getColor() method can decipher settings but only if they're in the system properties file.) In particular, you can use decode() to look up color settings in a resource file. The format of name is the same as that used by getColor(). If the contents of name do not translate to a 24-bit integer, the NumberFormatException run-time exception is thrown. To perform the equivalent of getColor(`myPackage.myClass.foreground`), without using system properties, see the following example. For a more extensive example using resource files, see Appendix A.

// Java 1.1 only
InputStream is = instance.getClass().getResourceAsStream("propfile");
Properties p = new Properties();
try {
    p.load (is);
    Color c = Color.decode(p.getProperty("myPackage.myClass.foreground"));
} catch (IOException e) {
    System.out.println ("error loading props...");
}

So far, the methods we have seen work with a color's red, green, and blue components. There are many other ways to represent colors. This group of methods allows you to work in terms of the HSB (hue, saturation, brightness) model. Hue represents the base color to work with: working through the colors of the rainbow, red is represented by numbers immediately above 0; magenta is represented by numbers below 1; white is 0; and black is 1. Saturation represents the color's purity, ranging from completely unsaturated (either white or black depending upon brightness) to totally saturated ( just the base color present). Brightness is the desired level of luminance, ranging from black (0) to the maximum amount determined by the saturation level.

public static float[] RGBtoHSB (int red, int green, int blue, float[] hsbvalues)

The RGBtoHSB() method allows you to convert a specific red, green, blue value to the hue, saturation, and brightness equivalent. RGBtoHSB() returns the results in two different ways: the parameter hsbvalues and the method's return value. The values of these are the same. If you do not want to pass an hsbvalues array parameter, pass null. In both the parameter and the return value, the three components are placed in the array as follows:

hsbvalues[0]	contains hue
hsbvalues[1]	contains saturation
hsbvalues[2]	contains brightness

public static Color getHSBColor (float hue, float saturation, float brightness)

The getHSBColor() method creates a Color object by using hue, saturation, and brightness instead of red, green, and blue values.

public static int HSBtoRGB (float hue, float saturation, float brightness)

The HSBtoRGB() method converts a specific hue, saturation, and brightness to a Color and returns the red, green, and blue values as an integer. As with the constructor, bits 16-23 represent the red component, 8-15 represent the green component, and 0-7 represent the blue component. Bits 24-31 are ignored.

public int hashCode ()

The hashCode() method returns a hash code for the color. The hash code is used whenever a color is used as a key in a Hashtable.

public boolean equals (Object o)

The equals() method overrides the equals() method of the Object to define equality for Color objects. Two Color objects are equivalent if their red, green, and blue values are equal.

public String toString ()

The toString() method of Color returns a string showing the color's red, green, and blue settings. For example System.out.println (Color.orange) would result in the following:

java.awt.Color[r=255,g=200,b=0]

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FontMetrics		SystemColor

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