The Java Lesson 29: The Color and Font classes

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Java Lesson 29 by Jon Huhtala: The Color and Font classes

The Color class

• Is part of the java.awt package

• Is an extension of the Object class

Object
	Color

• Encapsulates a particular color by mixing specified levels of red, green, and blue (RGB) light

• Is used extensively in graphical programming. The Color class makes it easy to specify the background and foreground (text) colors of components and set the pen color to be used in drawing lines and shapes.

• Contains predefined Color objects for 13 commonly used colors:

black

blue

cyan

darkGray

gray

green

lightGray

magenta

orange

pink

red

white

yellow

To reference one of these predefined objects you need only code an expression such as Color.yellow.

NOTE: Beginning with Java 2 version 1.4, the Color class has been expanded to contain capitalized versions of the above object references (Color.YELLOW, Color.PINK, etc.). Avoid the capitalized references if using older versions of Java.

• Provides several overloaded constructors for creating a custom color in a variety of ways. For example, to create a custom Color object that is brown one could code

Color brown = new Color(255, 128, 0);

where the parameters specify the level of red, green, and blue as integers in the range of 0 to 255.

• Has several useful methods. Commonly used methods are:

Method	Usage
getRed()	Returns the level of red in the range of 0 - 255
getBlue()	Returns the level of blue in the range of 0 - 255
getGreen()	Returns the level of green in the range of 0 - 255

Example:

import java.awt.*;
import java.awt.event.*;

public class App extends Frame implements WindowListener, ActionListener {

Button blot, more, less;
int greenLevel = 160;

public static void main(String[] args) {
App myWindow = new App("Green Blot");
myWindow.setSize(200,150);
myWindow.setVisible(true);
}

public App(String title) {
super(title);
setLayout(new BorderLayout());
addWindowListener(this);

blot = new Button("Green level is " + greenLevel);
blot.setForeground(Color.white);
blot.setBackground(new Color(0,greenLevel,0));
add(blot, BorderLayout.NORTH);

Panel moreOrLess = new Panel();
moreOrLess.setLayout(new GridLayout(1,2));
more = new Button("More Green");
more.setBackground(Color.black);
more.setForeground(Color.green);
more.addActionListener(this);
moreOrLess.add(more);
less = new Button("Less Green");
less.setBackground(Color.black);
less.setForeground(new Color(0,160,0));
less.addActionListener(this);
moreOrLess.add(less);
add(moreOrLess);
}

public void actionPerformed(ActionEvent e) {
if (e.getSource().equals(more)) {
if (greenLevel < 255) {
greenLevel += 5;
}
}
else {
if (greenLevel > 0) {
greenLevel -= 5;
}
}
blot.setBackground(new Color(0,greenLevel,0));
blot.setLabel("Green level is " + blot.getBackground().getGreen());
}

public void windowClosing(WindowEvent e) {
dispose();
System.exit(0);
}

public void windowOpened(WindowEvent e) {}
public void windowActivated(WindowEvent e) {}
public void windowIconified(WindowEvent e) {}
public void windowDeiconified(WindowEvent e) {}
public void windowDeactivated(WindowEvent e) {}
public void windowClosed(WindowEvent e) {}
}

Notes:

1. The sample declares three Button object references. blot is used to display the current level of green, more is used to increase the level of green, and less is used to decrease the level of green. The integer variable greenLevel will maintain the current level of green (from 0 to 255) and is initialized to 160.

2. In the constructor, blot is instantiated with a white text color and the initial level of green for its background color. It is placed in the NORTH of the frame's BorderLayout. A Panel object is then constructed having a GridLayout to hold the more and less buttons. The buttons are instantiated (with foreground color, background color, and registered action listener) and added to the panel which is then added to the application frame.

3. The actionPerformed() method determines which button (more or less) was clicked and adjusts the background color of blot either up or down accordingly. The label of blot is also changed to display the current level of green in its background color.

The Font class

• Is part of the java.awt package

• Is an extension of the Object class

Object
	Font

• Encapsulates a font for displaying text in a particular style and size

• Provides a constructor for creating a customized font. For example, to create a custom Font object for displaying text in 24 point italicized Serif one could code

Font myFont = new Font("Serif", Font.ITALIC, 24);

where the parameters specify the font name, font style, and point size.

• Can use any font available on the system. For compatibility, however, only "Serif", "SansSerif", and "Monospaced" are recommended. These are roughly equivalent to the "Times Roman", "Arial", and "Courier" fonts of Windows.

• Has public fields for specifying the font style. These can be referenced by coding

Font.BOLD

Font.ITALIC

Font.PLAIN

To combine styles, code an expression such as Font.BOLD + Font.ITALIC

• Provides for characters of any size specified as an integer point size

• Has many methods but few are needed to satisfy standard programming requirements. For more detail, consult the help facility of your IDE or the Java API documentation.

Example:

import java.awt.*;
import java.awt.event.*;

public class App extends Frame implements WindowListener {

Button b;

public static void main(String[] args) {
App myWindow = new App("Font sample");
myWindow.setSize(250,100);
myWindow.setVisible(true);
}

public App(String title) {
super(title);
addWindowListener(this);
b = new Button("Click me");
b.setBackground(Color.red);
b.setForeground(Color.white);
b.setFont(new Font("Monospaced", Font.PLAIN, 12));
add(b);
b.addActionListener(
new ActionListener() {
public void actionPerformed(ActionEvent e) {
b.setFont(new Font("SansSerif", Font.BOLD + Font.ITALIC, 4);
b.setLabel("Ouch!!");
}
}
);
}

public void windowClosing(WindowEvent e) {
dispose();
System.exit(0);
}

public void windowOpened(WindowEvent e) {}
public void windowActivated(WindowEvent e) {}
public void windowIconified(WindowEvent e) {}
public void windowDeiconified(WindowEvent e) {}
public void windowDeactivated(WindowEvent e) {}
public void windowClosed(WindowEvent e) {}
}

Notes:

1. The sample declares a single Button object reference (b).

2. In the constructor, b is instantiated with a red background color, a white text color, and a "Monospaced", plain, 10 point font. It is added to the CENTER of the frame's BorderLayout (both by default) and its ActionListener is both registered and defined using an anonymous inner interface. When using this technique, the interface isn't implemented in the class header. When the user clicks the button, its font is changed to 48 point, bold, italicized, "SansSerif" and its label is modified. A slight delay may be noticed as these operations are time consuming in Java.

Lab exercise for Ferris students

E-mail your answers to this assignment no later than the due date listed in the class schedule.

Review questions

1. Assuming that all unseen code is correct and that the container has a foreground color of blue, what will result from attempting to compile and execute the following code with a Java 2 version 1.2 compiler? The line numbers are for reference purposes only.

1 2 3

Button blue = new Button("Am I blue?"); blue.setBackground(Color.BLUE); add(blue);

1. Compilation will fail at line 2

2. Compilation will fail at line 3

3. Compilation will succeed but a runtime error will occur

4. Compilation will succeed. A button with the text "Am I blue?" and having white letters on a blue background will be added to the container.

5. Compilation will succeed but the button's text will not be visible.

2. If somePanel is a container, code a single statement to set its text color to a custom shade having maximum levels of red and blue, but no green.

3. Which of the following will set a component's text to display in yellow, 18 point, bold, serif if using Java 2 version 1.2?

1. setForeground(Color.YELLOW));
   setFont(new Font("Serif", Font.BOLD, 1);

2. setForeground(Color.YELLOW));
   setFont(new Font("Serif", Font.bold, 1);

3. setForeground(Color.yellow));
   setFont(new Font("Serif", Font.BOLD, 1);

4. setForeground(Color.yellow));
   setFont(new Font("Serif", Font.bold, 1);

5. setForeground(Color.yellow));
   setFont(new Font("Serif", BOLD, 1);

4. What background color will result from the following?

setBackground(Color.gray.blue);

1. The statement will not compile

2. Compilation succeeds but a runtime error will occur

3. A mix of gray and blue

4. gray

5. blue

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