Simple Applet Display Methods

Simple Applet Display Methods

As we’ve mentioned, applets are displayed in a window, and AWT-based applets use the AWT to perform input and output. Although we will examine the methods, procedures, and techniques related to the AWT in subsequent chapters, a few are described here, because we will use them to write sample applets. (Remember, Swing-based applets are described later in this book.)

As described in Chapter 13, to output a string to an applet, use drawString( ), which is a member of the Graphics class. Typically, it is called from within either update( ) or paint( ). It has the following general form:

void drawString(String message, int x, int y)

Here, message is the string to be output beginning at x,y. In a Java window, the upper-left corner is location 0,0. The drawString( ) method will not recognize newline characters. If you want to start a line of text on another line, you must do so manually, specifying the precise X,Y location where you want the line to begin. (As you will see in later chapters, there are techniques that make this process easy.)

To set the background color of an applet’s window, use setBackground( ). To set the foreground color (the color in which text is shown, for example), use setForeground( ). These methods are defined by Component, and they have the following general forms:

void setBackground(Color newColor) void setForeground(Color newColor)

Here, newColor specifies the new color. The class Color defines the constants shown here that can be used to specify colors:

Color.black

Color.blue

Color.cyan

Color.darkGray

Color.gray

Color.green

Color.lightGray

Color.magenta

Color.orange

Color.pink

Color.red

Color.white

Color.yellow

Uppercase versions of the constants are also defined.

The following example sets the background color to green and the text color to red:

setBackground(Color.green);

setForeground(Color.red);

A good place to set the foreground and background colors is in the init( ) method. Of course, you can change these colors as often as necessary during the execution of your applet.

You can obtain the current settings for the background and foreground colors by calling getBackground( ) and getForeground( ), respectively. They are also defined by Component and are shown here:

Color getBackground( ) Color getForeground( )

Here is a very simple applet that sets the background color to cyan, the foreground color to red, and displays a message that illustrates the order in which the init( ), start( ), and paint( ) methods are called when an applet starts up:

/*    A simple applet that sets the foreground and background colors and outputs a string. */

import java.awt.*; import java.applet.*; /*

<applet code="Sample" width=300 height=50> </applet>

*/

public class Sample extends Applet{ String msg;

    set the foreground and background colors. public void init() {

setBackground(Color.cyan);

setForeground(Color.red); msg = "Inside init( ) --";

}

    //Initialize the string to be displayed.

    public void start() {

msg += " Inside start( ) --";

}

    //Display msg in applet window.

public void paint(Graphics g) { msg += " Inside paint( )."; g.drawString(msg, 10, 30);

}

}

Sample output is shown here:

The methods stop( ) and destroy( ) are not overridden, because they are not needed by this simple applet.