Making a button

Thursday Mar 1st 2001
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Making a button is quite simple: you just call the Button constructor with the label you want on the button. (You can also use the default constructor if you want a button with no label, but this is not very useful.) Usually you’ll want to create a handle for the button so you can refer to it later.

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Making a button is quite simple: you just call the Button constructor with the label you want on the button. (You can also use the default constructor if you want a button with no label, but this is not very useful.) Usually you’ll want to create a handle for the button so you can refer to it later.

The Button is a component, like its own little window, that will automatically get repainted as part of an update. This means that you don’t explicitly paint a button or any other kind of control; you simply place them on the form and let them automatically take care of painting themselves. So to place a button on a form you override init( ) instead of overriding paint( ):

//: Button1.java
// Putting buttons on an applet
import java.awt.*;
import java.applet.*;
 
public class Button1 extends Applet {
  Button 
    b1 = new Button("Button 1"), 
    b2 = new Button("Button 2");
  public void init() {
    add(b1);
    add(b2);
  }
} ///:~ 

It’s not enough to create the Button (or any other control). You must also call the Applet add( ) method to cause the button to be placed on the applet’s form. This seems a lot simpler than it is, because the call to add( ) actually decides, implicitly, where to place the control on the form. Controlling the layout of a form is examined shortly.

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