Java Programming ... From the Grounds Up Part 4

Java Programming ... From the Grounds Up
Part 4

by Mark C. Reynolds

Packaging up your code

Advanced Java Classes

The collection of Java classes is structured as a tree, in which each node has exactly one parent. Since Java classes can only inherit from one class at a time, it is said to support a single-class inheritance hierarchy.

FIGURE 2
Important components of the Java hierarchy.

 java.lang Boolean Character Integer Long  Float  Double String Class  Math Number Object  Process System Thread java.awt Button Canvas  Checkbox Choice Color Dimension Event FileDialog Font Graphics Image  Insets Label List  Menu MenuBar MenuItem Panel Point Polygon  Rectangle Scrollbar TextArea TextField Window java.io DataInput  DataInputStream InputStream DataOutput  DataOutputStream OutputStream File  FileInputStream FileOutputStream FilenameFilter FilterInputStream FilterOutputStream PrintStream  RandomAccessFile StreamTokenizer java.net ContentHandler InetAddress  ServerSocket URL  URLConnection URLStreamHandler java.applet Applet AudioClip java.util BitSet Date Dictionary Enumeration Hashtable Properties Random Stack  StringTokenizer Vector 

The top of the Java class hierarchy is organized into a set of related classes, called packages. The main Java packages are java.lang, java.net, java.io, java.awt, java.util, and java.applet. The java.lang package implements the basic components of the Java language, including string manipulation, mathematical functions, and conversion operations such as the simple string-to-integer one seen in Primes.java. The java.net package contains the network access functions, including those associated with opening a URL and getting its contents. The java.io package handles all kinds of input and output, implementing various forms of streaming (much like stdin and stdout in C or cin and cout in C++). Graphics are handled by java.awt. "AWT" is said to stand for "Another Window Toolkit" or "Advanced Window Toolkit," depending on who you ask. The AWT implements standard graphic components such as menus, panels, buttons, and checkboxes. The AWT also implements a number of sophisticated image manipulation functions within the java.awt.image subpackage. If you have ever programmed Windows or Macintosh graphics, used X or a higher level toolkit such as Tk, then AWT will seem very familiar. The java.util package has additional utility functions for string, vector and stack manipulation, hashing, date conversion, and a number of other goodies. Finally, java.applet is a very special package that actually creates a subclass of Applet whenever a new applet is produced.