Collection and Utility Classes

The java.util package contains a number of useful classes that support important functionality as part of the Java API. These classes provide basic utilities that you frequently end up either writing yourself or purchasing from a third party when you are working in other languages. The creators of Java tried to capture the best concepts from several programming languages, and the results of this are clearly seen in the collection and utility classes. This aspect of Java was in particular influenced by Smalltalk, which is a pure object-oriented language highly regarded for its abundance of utility classes.

This chapter walks you through the majority of the java.util classes with examples and guidelines on their uses. Those classes that are not covered here relate to threads, event handling, and internationalization and are covered in later chapters where their purposes can be more clearly demonstrated.

The java.util package focuses mostly on collection objects ”that is, objects that contain or hold other objects. In addition to the collections, the package also adds support for property files, dates, bit manipulation, random number generation, and a carryover from Smalltalk called observables.

Note

Smalltalk was the first object-oriented language to become popular. It was developed in the '70s at Xerox's Palo Alto Research Center and demonstrates many of the strengths of OOP. Everything in Smalltalk is an object, and all operations are performed by passing messages between objects. The language is highly integrated with its development environment, which has served as a model for both operating systems and development tools that have followed.