The first two lines of the HelloWorld applet import two classes:
JApplet
andGraphics
.import javax.swing.JApplet; import java.awt.Graphics; public class HelloWorld extends JApplet { public void paint(Graphics g) { g.drawRect(0, 0, getSize().width - 1, getSize().height - 1); g.drawString("Hello world!", 5, 15); } }If you removed the first two lines, the applet could still compile and run, but only if you changed the rest of the code like this:
public class HelloWorld extends javax.swing.JApplet { public void paint(java.awt.Graphics g) { g.drawString("Hello world!", 5, 15); } }As you can see, importing the
JApplet
andGraphics
classes lets the program refer to them later without any prefixes. Thejavax.swing.
andjava.awt.
prefixes tell the compiler which packages it should search for theJApplet
andGraphics
classes.Both the
javax.swing
andjava.awt
packages are part of the core Java API always included in the Java environment.The
javax.swing
package contains classes for building Java graphical user interfaces (GUIs), including applets.The
java.awt
package contains the most frequently used classes in the Abstract Window Toolkit (AWT).Besides importing individual classes, you can also import entire packages. Here's an example:
import javax.swing.*; import java.awt.*; public class HelloWorld extends JApplet { public void paint(Graphics g) { g.drawRect(0, 0, getSize().width - 1, getSize().height - 1); g.drawString("Hello world!", 5, 15); } }In the Java language, every class is in a package. If the source code for a class doesn't have a package statement at the top, declaring the package the class is in, then the class is in the default package. Almost all of the example classes in this tutorial are in the default package. See Creating and Using Packages for information on using the
package
statement.