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The package java.util, as its name implies, provides a number of useful classes.

(Note: It should not be considered a "utility" package separate from the rest of the language. It is part and parcel of the library, and Java depends heavily on several of the classes in this package.)

The Old Collections Classes

HashTable and Properties

HashTable implements a hashtable or associative array. It allows abritrary objects to be stored and retrieved by arbitrary keys.

Properties, a subclass of HashTable, is used to store the Java system properties list.

Vector

Implements an array of objects that grows as needed when objects are added.

Stack

Implements a LIFO stack on which objects may be pushed and from which they may be popped.

Enumeration

Interface which provides a simple and consistent way to loop through all the elements contained within some kind of object or data structure.

The Collections Framework

Many interfaces and classes used to implement the powerful Java collections framework.  We discussed these classes in some detail, earlier.

Date, Calendar, and TimeZone

The Date class represents a date and time, using a millisecond representation.

The Calendar class manipulates dates using years, months, days, hours, minutes, etc.

The TimeZone class is used in conjunction with dates.

ResourceBundle, ListResourceBundle, PropertyResourceBundle

Represent a "bundle" of localized resources that are read in by an internationalized Java program at run-time.

BitSet

Implements an arbitrary-size array of bits.

Random

Generates and returns pseudo-random numbers in a variety of forms.

StringTokenizer

Parses a string into tokens.

Observer and Observable

Provide infrastructure for implementing the object-oriented model-view paradigm in Java.

This page was last modified on 02 October, 2007