Java Programming
Classes, objects, and methods
- Only a small number of operations are defined in Java. Many of the methods and identifiers needed to run a Java program are provided as a collection of libraries.
- A package is a collection of related classes and that every package has a name.
- The term class is broadly used. It is used to create Java programs (either application or applet), it is used to group a set of related operations, and it is used to allow users to create their own data types.
- Each of these operations is implemented using the Java mechanism of methods.
- A method is a set of instructions designed to accomplish a specific task.
- To make use of the existing classes, methods, and identifiers, you must specify the packages that contain the appropriate information using the reserved word import.
Common Java packages
| Package name | Description |
|---|---|
| java.lang | Provides classes fundamental to Java, including classes that work with primitive data types, strings, and math functions. |
| java.text | Provides classes to handle text, dates, and numbers. |
| java.util | Provides various utility classes including those for working with collections. |
| java.io | Provides classes to read data from files and to write data to files. |
| java.sql | Provides classes to read data from databases and to write data to databases. |
| java.applet | An older package that provides classes to create an applet. |
| java.awt | An older package called the Abstract Window Toolkit (AWT) that provides classes to create graphical user interfaces. |
| java.awt.event | A package that provides classes necessary to handle events. |
| javax.swing | A newer package called Swing that provides classes to create graphical user interfaces and applets. |