Module 1, Part 8
API Packages
Java comes with over 300 predefined packages, called API (Application Programmer Interface)
packages. Some of the classes in the packages, like class String(in package
java.lang) are essentially built in to the language.
Others provide classes and methods for reading and writing files, dealing
with URLs (addresses of pages on the world wide web, for example), and
constructing GUIs (Graphical User Interfaces). As you use Java more and
more, you will get familiar with the API that comes with Java and rely
on it more and more.
We will only cover a few of them in this part. Here are the
API specs
for Java 1.6 if you wish to learn more.
Contents
1. Using API Specs on the Web
Web Lecture
Reading:
Lecture Notes
Gries/Gries, Appendix II.1, p. 493–496.
Comments:
We browse the API specs on the web, showing you what they look like and how to find what you want.
2. Wrapper Class Integer
Web Lecture
Reading:
Lecture Notes
(Lecture Slides)
Gries/Gries, Sec. 5.5.1, pp. 172–174.
Comments:
Primitive type int has a corresponding wrapper class, Integer.
Each instance of Integer"wraps", or contains, an int value. Class
Integer(1) allows us to treat an int value as an object and
(2) provides a place to put constants and functions that deal with int values.
3. Wrapper Classes for Other Primitive Types
Reading:
Lecture Notes
Comments:
Each primitive type has a corresponding wrapper class. The html page of lecture notes is
only a summary. For details, look at the API specs on the web or the ProgramLive CD, page 5-1.
4. Autoboxing
Web Lecture
Reading:
Lecture Notes
(Sample Code)
Comments:
Autoboxing, which was introduced to Java in version 5, provides
for automatic conversion between each primitive type and its wrapper
class. Autoboxing is not discussed in the current edition of Gries/Gries.
5. Class ArrayList
Web Lecture
Reading:
Lecture Notes
(Lecture Slides)
Gries/Gries, Sec. 5.3, pp. 184–189, covers an older class
Vector, instead of ArrayList. The
concepts are the same, but the methods will be slightly different
Comments:
An instance contains a list of objects, and one can add elements
to the list, delete them, and retrieve them.
6. Constraining ArrayLists
Web Lecture
Reading:
Lecture Notes
(Lecture Slides)
Gries/Gries, Sec. 5.3, pp. 184–189, covers an older class
Vector, instead of ArrayList. The
concepts are the same, but the methods will be slightly different
Comments:
This brief web lecture shows how to constrain elements of a list to
have a certain class, thus reducing the chance of making errors
by adding the wrong objects to the list.
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