Java in a Nutshell, 5th Edition

Name

Package java.util

Synopsis

The java.util package defines a number of useful classes, primarily collections classes that are useful for working with groups of objects. This package should not be considered merely a utility package that is separate from the rest of the language; it is an integral and frequently used part of the Java platform.

The most important classes in java.util are the collections classes. Prior to Java 1.2, these were Vector, a growable list of objects, and Hashtable, a mapping between arbitrary key and value objects. Java 1.2 adds an entire collections framework consisting of the Collection, Map, Set, List, SortedMap, and SortedSet interfaces and the classes that implement them. Other important classes and interfaces of the collections framework are Comparator, Collections, Arrays, Iterator, and ListIterator. Java 1.4 extends the Collections framework with the addition of new Map and Set implementations, and a new RandomAccess marker interface used by List implementations. Java 5.0 adds a Queue collection interface and implementations. It also adds EnumSet and EnumMap which efficiently implement the Set and Map interfaces for use with enumerated types. Most importantly, Java 5.0 modifies all collection interfaces and classes to be generic types, which enable type-safe collections such as List<String>. BitSet is a related class that is not actually part of the Collections framework (and is not even a set). It provides a very compact representation of ...