Basic Java Objects

The Java language has its objects organized in the following packages:

java.lang

Package that contains essential Java classes, including numerics, strings, objects, compiler, runtime, security, and threads. This is the only package that is automatically imported into every Java program.

java.io

Package that provides classes to manage input and output streams to read data from and write data to files, strings, and other sources.

java.awt

Package that provides an integrated set of classes to manage user interface components such as windows, dialog boxes, buttons, checkboxes, lists, menus, scrollbars, and text fields. (AWT = Abstract Window Toolkit)

java.util

Package that contains miscellaneous utility classes, including generic data structures, bit sets, time, date, string manipulation, random number generation, system properties, notification, and enumeration of data structures.

java.net

Package that provides classes for network support, including URLs, TCP sockets, UDP sockets, IP addresses, and a  binary-to-text converter.

java.awt.image

Package that provides classes for managing image data, including color models, cropping, color filtering, setting pixel   values, and grabbing snapshots.

java.awt.peer

Package that connects AWT components to their platform-specific implementations (such as Motif widgets or Microsoft Windows controls).

java.applet

Package that enables the creation of applets through the Applet class. It also provides several interfaces that connect an applet to its document and to resources for playing audio.

 Before you can use any of the classes in these packages, you need to import the object, or objects, using the import statement. For example:

import java.awt.Graphics;
import java.awt.Button;
import java.applet.*;

will import the Graphics and Button classes from the java.awt package, and all classes in the java.applet packages. You can also create your own packages, but we will not do that for a while. For now, we will be concerned with some of the basic classes we need to understand to create reasonably nice Java programs. One of the basic classes to create standalone Java programs is the Frame class. A Frame is the basic Java version of a Window, complete with close boxes, resizable, and menu bar, if desired. Most standalone programs have at least one frame object. Here is the definition of the Frame class with some of its methods:

public class java.awt.Frame extends java.awt.Window
                            implements java.awt.MenuContainer
{   // Constructors
    public Frame();
    public Frame(String  title);
    // Selected Methods
    public void dispose();
    public MenuBar getMenuBar();
    public String getTitle();
    public void setMenuBar(MenuBar  mb);
    public void setTitle(String  title);
}