WebReference.com - Part 4 of chapter 5 from Beginning Java 2 SDK 1.4 Edition, Wrox Press Ltd (4/8)

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Beginning Java 2 SDK 1.4 Edition

Standard Packages

All of the standard classes that are provided with Java are stored in standard packages. There is a substantial (more than 130 in SDK1.4) and growing list of standard packages but some of the ones you may hear about quite frequently are:

java.lang	Contains classes that are fundamental to Java (e.g. the Math class) and all of these are available in your programs automatically. You do not need an import statement to include them.
java.io	Contains classes supporting stream input/output operations.
java.nio	Contains classes supporting new input/output operations in JDK1.4--especially with files.
java.nio.channels	Contains more classes supporting new input/output operations in JDK1.4--the ones that actually read and write files.
java.awt	Contains classes that support Java's Graphical User Interface (GUI). While you can use these classes for GUI programming, it is almost always easier and better to use the alternative Swing classes.
javax.swing	Provides classes supporting the 'Swing' GUI components. These are not only more flexible and easier to use than the java.awt equivalents, but they are also implemented largely in Java with minimal dependency on native code.
javax.swing.border	Classes to support generating borders around Swing components.
javax.swing.event	Classes supporting event handling for Swing components.
java.awt.event	Contains classes that support event handling.
java.awt.geom	Contains classes for drawing and operating with 2D geometric entities.
java.awt.image	Contains classes to support image processing.
java.applet	This contains classes that enable you to write applets--programs that are embedded in a web page.
java.util	This contains classes that support a range of standard operations for managing collections of data, accessing date and time information, and analyzing strings.

The standard packages and the classes they contain cover an enormous amount of ground, so even in a book of this size it is impossible to cover them all exhaustively. There are now many more classes in the standard packages with JDK1.4 than there are pages in this book. However, we will be applying some classes from all of the packages in the table above, plus one or two others besides, in later chapters of the book.

Standard Classes Encapsulating the Basic Data Types

You saw in the previous chapter that we have classes available that allow you to define objects that encapsulate each of the basic data types in Java. These classes are:

Boolean	Character	Byte
Short	Integer	Long
Float	Double

These are all contained in the package java.lang along with quite a few other classes such as the String and StringBuffer classes that we saw in Chapter 4, and the Math class. Each of these classes encapsulates the corresponding basic type, and includes methods for manipulating and interrogating objects of the class, as well as a number of static methods that provide utility functions for the underlying basic types. Each of the classes corresponding to a numeric type provides a static toString() method to convert to a String object, as we saw in the last chapter. There is also a non-static toString() method in all of these classes that returns a String representation of a class object.

The classes encapsulating the numeric basic types each contain the static final constants MAX_VALUE and MIN_VALUE that define the maximum and minimum values that can be represented. The floating-point classes also define the constants POSITIVE_INFINITY, NEGATIVE_INFINITY, and NaN (stands for Not a Number as it is the result of 0/0), so you can use these in comparisons. Alternatively, you can test floating point values with the static methods isInfinite() and isNaN()--you pass your variable as an argument, and the methods return true for an infinite value or the NaN value respectively. Remember that an infinite value can arise without necessarily dividing by zero. Any computation that results in an exponent that is too large to be represented will produce either POSITIVE_INFINITY or NEGATIVE_INFINITY.

Conversely there are methods to convert from a String to a basic type. For example, the static parseInt() member of the class Integer accepts a String representation of an integer as an argument, and returns the equivalent value as type int. An alternative version of this method accepts a second argument of type int that specifies the radix to be used. If the String object cannot be parsed for any reason, if it contains invalid characters for instance, the method will throw an exception of type NumberFormatException. All the standard classes define methods to parse strings--parseShort(), parseByte(), and parseLong().

There are many other operations supported by these classes so it is well worth browsing the JDK documentation for them.

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Created: July 29, 2002
Revised: July 29, 2002

URL: https://webreference.com/programming/java/beginning/chap5/4/4.html