Java™ Application Development on Linux - Dator

62Chapter 3An Experienced Programmer’s Introduction to JavaTable 3.2 (Continued)Return typeMethodDescriptionStringsubstring(int first, int last)Returns a string starting at position firstand up to, but not including, characterposition last. If last is greater than thelength of the String, or last is less thanfirst, it throws an IndexOutOfBoundsexception.3.2.2.3 Other Classes: Reading JavadocJava comes with a huge collection of existing classes for you to use. The simplestones are just wrappers for the primitive classes. There is an int primitive datatype, but Java provides an Integer class, so that you can have an integer as anobject. Similarly, there are classes for Long, Float, Boolean, and so on. Suchclasses aren’t nearly as interesting as the myriad other classes that come withJava. These others provide objects for doing I/O, networking, 2D and 3Dgraphics, graphical user interfaces (GUIs), and distributed computing. Javaprovides ready-to-use classes for strings, math functions, and for special kindsof data structures like trees and sets and hash tables. There are classes to helpyou with the manipulation of HTML, XML, and SQL, as well as classes forsound, music, and video. All these objects can be yours to use and enjoy if youjust learn the magic of reading Javadoc—online documentation for Java classes.The documentation for all these classes is viewed with a Web browser. (In afollowing chapter we’ll describe how you can make Javadoc documents for theclasses that you write, too.)The online version of the API documentation can be found athttp://java.sun.com/j2se/1.4.2/docs/api/for Java 1.4.2. (Similarly, put 1.5.1 or whatever version you want at theappropriate place in the URL.) When displayed, it shows a three-frame page,as seen in Figure 3.1, except that we’ve overlaid the image with three labels:A, B, and C.The upper left frame of the Javadoc display, the area labeled with A in ourfigure, lists all the packages that are part of Java 2 Standard Edition (J2SE).While there are many other packages of classes available for Java, these classesare the standard ones available without any other class libraries, with no