java.util : The Collections Framework

Chapter 18

java.util Part 1: The Collections  Framework

This chapter begins our examination of java.util. This important package contains a large assortment of classes and interfaces that support a broad range of functionality. For example, java.util has classes that generate pseudorandom numbers, manage date and time, observe events, manipulate sets of bits, tokenize strings, and handle formatted data. The java.util package also contains one of Java’s most powerful subsystems: the Collections Framework. The Collections Framework is a sophisticated hierarchy of interfaces and classes that provide state-of-the-art technology for managing groups of objects. It merits close attention by all programmers.

Because java.util contains a wide array of functionality, it is quite large. Here is a list of its top-level classes:

AbstractCollection

AbstractList

AbstractMap

AbstractQueue

AbstractSequentialList

AbstractSet

ArrayDeque

ArrayList

Arrays

Base64 (Added by JDK 8.)

BitSet

Calendar

FormattableFlags

Formatter

GregorianCalendar

HashMap

HashSet

Hashtable

IdentityHashMap

IntSummaryStatistics (Added by JDK 8.)

LinkedHashMap

LinkedHashSet

LinkedList

ListResourceBundle

Properties

PropertyPermission

PropertyResourceBundle

Random

ResourceBundle

Scanner

ServiceLoader

SimpleTimeZone

Spliterators (Added by JDK 8.)

SplitableRandom (Added by JDK 8.)

Stack

StringJoiner (Added by JDK 8.)

Collections

Currency

Date

Dictionary

DoubleSummaryStatistics

(Added by JDK 8.)

EnumMap

EnumSet

EventListenerProxy

EventObject

Locale

LongSummaryStatistics (Added by JDK 8.)

Objects

Observable

Optional (Added by JDK 8.)

OptionalDouble (Added by JDK 8.)

OptionalInt (Added by JDK 8.)

OptionalLong (Added by JDK 8.)

PriorityQueue

StringTokenizer

Timer

TimerTask

TimeZone

TreeMap

TreeSet

UUID

Vector

WeakHashMap

The interfaces defined by java.util are shown next:

Collection

Comparator

Deque

Enumeration

EventListener

Formattable

Iterator

List

ListIterator

Map

Map.Entry

NavigableMap

NavigableSet

Observer

PrimitiveIterator (Added by JDK 8.)

PrimitiveIterator.OfDouble (Added by JDK 8.)

PrimitiveIterator.OfInt (Added by JDK 8.)

PrimitiveIterator.OfLong (Added by JDK 8.)

Queue

RandomAccess

Set

SortedMap

SortedSet

Spliterator (Added by JDK 8.)

Spliterator.OfDouble (Added by JDK 8.)

Spliterator.OfInt (Added by JDK 8.)

Spliterator.OfLong (Added by JDK 8.)

Spliterator.OfPrimitive (Added by JDK 8.)

Because of its size, the description of java.util is broken into two chapters. This chapter examines those members of java.util that are part of the Collections Framework. Chapter 18 discusses its other classes and interfaces.