The Java TM Tutorial

| Start of Tutorial > Start of Trail > Start of Lesson | Search

Trail: Getting Started
Lesson: The "Hello World" Applet

## Importing Classes and Packages

> The first two lines of the following listing import two classes used in the applet: `Applet` and `Graphics`.

> >     import java.applet.Applet;
> >     import java.awt.Graphics;

> >     public class HelloWorld extends Applet {
> >         public void paint(Graphics g) {
> >             g.drawString("Hello world!", 50, 25);
> >         }
> >     }

> 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 java.applet.Applet {
> >         public void paint(java.awt.Graphics g) {
> >             g.drawString("Hello world!", 50, 25);
> >         }
> >     }

> As you can see, importing the `Applet` and `Graphics` classes lets the program refer to them later without any prefixes. The `java.applet.` and `java.awt.` prefixes tell the compiler which packages it should search for the `Applet` and `Graphics` classes. Both the `java.applet` and `java.awt` packages are part of the core Java API -- API that every Java program can count on being in the Java environment. The `java.applet` package contains classes that are essential to Java applets. The `java.awt` package contains the most frequently used classes in the Abstract Window Toolkit (AWT), which provides the Java graphical user interface (GUI).

> You might have noticed that the "Hello World" application example from the previous lesson uses the `System` class without any prefix, and yet does not import the `System` class. The reason is that the `System` class is part of the `java.lang` package, and everything in the `java.lang` package is automatically imported into every Java program.

> Besides importing individual classes, you can also import entire packages. Here's an example:

> >     import java.applet.*;
> >     import java.awt.*;

> >     public class HelloWorld extends Applet {
> >         public void paint(Graphics g) {
> >             g.drawString("Hello world!", 50, 25);
> >         }
> >     }

> 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.

> Within a package, all classes can refer to each other without prefixes. For example, the `java.awt Component` class refers to the `java.awt Graphics` class without any prefixes, without importing the `Graphics` class.

| Start of Tutorial > Start of Trail > Start of Lesson | Search