FirstAppletpublic class FirstApplet extends Applet implements ActionListener| FirstApplet is a simple applet that changes color when you click on a
Draw button. |
| Fields Summary |
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| boolean | requested |
| Methods Summary |
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| public void | actionPerformed(java.awt.event.ActionEvent e)actionPerformed is called when a "high level" action happens
(like the user pushing a Button!) in one of the components for
which we are registered as an actionListener. In this applet,
we just toggle the state of the "requested" flag, to draw or
not to draw.
// Invert or "toggle" the state of the draw request.
requested = !requested;
repaint(); // Then ask AWT to repaint us.
| | public void | init()init() is an Applet method called by the browser to initialize.
In this program, we use it to initialize the "requested" flag
to false, create a Draw button and add it to the Applet, and
hang an ActionListener (which is also this Applet itself) onto
the Button.
requested = false;
Button b;
b = new Button("Draw");
add(b); // connect Button into Applet
b.addActionListener(this); // connect Actions back to Applet
| | public void | paint(java.awt.Graphics g)paint() is an AWT Component method, called when the
component needs to be painted. We look at the draw flag and,
if we've turned it on in actionPerformed, we draw some colored
boxes in the Applet's window.
/* If the drawn button has been pressed, draw something */
if (requested) {
int w = getSize().width, h=getSize().height;
g.setColor(Color.yellow);
g.fillRect(0, 0, w/2, h);
g.setColor(Color.green);
g.fillRect(w/2, 0, w, h);
g.setColor(Color.black);
g.drawString("Welcome to Java", 50, 50);
}
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