Package java.util | Java In A Nutshell, 5th Edition

Package java.util

Java 1.0

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 an arbitrary- size array or list of boolean values or bits. Its API was substantially enhanced in Java 1.4.

The other classes of the package are also quite useful. Date , Calendar , and TimeZone work with dates and times. Currency represents a national currency. Locale represents the language and related text formatting conventions of a country, region, or culture. ResourceBundle and its subclasses represent a bundle of localized resources that are read in by an internationalized program at runtime. Random generates and returns pseudorandom numbers in a variety of forms. StringTokenizer is a simple parser that breaks a string into tokens. In Java 1.3 and later, Timer and TimerTask provide a powerful API for scheduling code to be run by a background thread, once or repetitively, at a specified time in the future. In Java 5.0, the Formatter class enables poweful formatted text output in the style of the C programming language's printf( ) function. The Java 5.0 Scanner class is a text tokenizer or scanner that can also parse numbers and match tokens based on regular expressions.

Interfaces

 public interface  Collection  <E> extends Iterable<E>; public interface  Comparator  <T>; public interface  Enumeration  <E>; public interface  EventListener  ; public interface  Formattable  ; public interface  Iterator  <E>; public interface  List  <E> extends Collection<E>; public interface  ListIterator  <E> extends Iterator<E>; public interface  Map  <K, V>; public interface  Map.Entry  <K, V>; public interface  Observer  ; public interface  Queue  <E> extends Collection<E>; public interface  RandomAccess  ; public interface  Set  <E> extends Collection<E>; public interface  SortedMap  <K, V> extends Map<K, V>; public interface  SortedSet  <E> extends Set<E>;

Enumerated Types

 public enum  Formatter.BigDecimalLayoutForm  ;

Collections

 public abstract class  AbstractCollection  <E> implements Collection<E>;    public abstract class  AbstractList  <E> extends AbstractCollection<E>          implements List<E>;       public abstract class  AbstractSequentialList  <E> extends AbstractList<E>;          public class  LinkedList  <E> extends AbstractSequentialList<E>                       implements List<E>, Queue<E>, Cloneable, Serializable;       public class  ArrayList  <E> extends AbstractList<E> implements List<E>,          RandomAccess, Cloneable, Serializable;       public class  Vector  <E> extends AbstractList<E> implements List<E>,          RandomAccess, Cloneable, Serializable;          public class  Stack  <E> extends Vector<E>;    public abstract class  AbstractQueue  <E> extends AbstractCollection<E>          implements Queue<E>;       public class  PriorityQueue  <E> extends AbstractQueue<E>          implements Serializable;    public abstract class  AbstractSet  <E> extends AbstractCollection<E>          implements Set<E>;       public abstract class  EnumSet  <E extends Enum<E>> extends AbstractSet<E>          implements Cloneable, Serializable;       public class  HashSet  <E> extends AbstractSet<E> implements Set<E>,          Cloneable, Serializable;          public class  LinkedHashSet  <E> extends HashSet<E> implements Set<E>,          Cloneable, Serializable;       public class  TreeSet  <E> extends AbstractSet<E> implements SortedSet<E>,          Cloneable, Serializable; public abstract class  AbstractMap  <K, V> implements Map<K, V>;    public class  EnumMap  <K extends Enum<K>, V> extends AbstractMap<K, V>          implements Serializable, Cloneable;    public class  HashMap  <K, V> extends AbstractMap<K, V> implements Map<K, V>,          Cloneable, Serializable;       public class  LinkedHashMap  <K, V> extends HashMap<K, V>          implements Map<K, V>;    public class  IdentityHashMap  <K, V> extends AbstractMap<K, V>          implements Map<K, V>, Serializable, Cloneable;    public class  TreeMap  <K, V> extends AbstractMap<K, V>          implements SortedMap<K, V>, Cloneable, Serializable;    public class  WeakHashMap  <K, V> extends AbstractMap<K, V> implements Map<K, V>; public class  Hashtable  <K, V> extends Dictionary<K, V> implements Map<K, V>,          Cloneable, Serializable;    public class  Properties  extends Hashtable<Object, Object>;

Events

 public class  EventObject  implements Serializable;

Other Classes

 public class  Arrays  ; public class  BitSet  implements Cloneable, Serializable; public abstract class  Calendar  implements Serializable, Cloneable, Comparable<Calendar>;    public class  GregorianCalendar  extends Calendar; public class  Collections  ; public final class  Currency  implements Serializable; public class  Date  implements Serializable, Cloneable, Comparable<Date>; public abstract class  Dictionary  <K, V>; public abstract class  EventListenerProxy  implements EventListener; public class  FormattableFlags  ; public final class  Formatter  implements java.io.Closeable, java.io.Flushable; public final class  Locale  implements Cloneable, Serializable; public class  Observable  ; public final class  PropertyPermission  extends java.security.BasicPermission; public class  Random  implements Serializable; public abstract class  ResourceBundle  ;    public abstract class  ListResourceBundle  extends ResourceBundle;    public class  PropertyResourceBundle  extends ResourceBundle; public final class  Scanner  implements Iterator<String>; public class  StringTokenizer  implements Enumeration<Object>; public class  Timer  ; public abstract class  TimerTask  implements Runnable; public abstract class  TimeZone  implements Cloneable, Serializable;    public class  SimpleTimeZone  extends TimeZone; public final class  UUID  implements Serializable, Comparable<UUID>;

Exceptions

 public class  ConcurrentModificationException  extends RuntimeException; public class  EmptyStackException  extends RuntimeException; public class  FormatterClosedException  extends IllegalStateException; public class  IllegalFormatException  extends IllegalArgumentException;    public class  DuplicateFormatFlagsException  extends IllegalFormatException;    public class  FormatFlagsConversionMismatchException  extends IllegalFormatException;    public class  IllegalFormatCodePointException  extends IllegalFormatException;    public class  IllegalFormatConversionException  extends IllegalFormatException;    public class  IllegalFormatFlagsException  extends IllegalFormatException;    public class  IllegalFormatPrecisionException  extends IllegalFormatException;    public class  IllegalFormatWidthException  extends IllegalFormatException;    public class  MissingFormatArgumentException  extends IllegalFormatException;    public class  MissingFormatWidthException  extends IllegalFormatException;    public class  UnknownFormatConversionException  extends IllegalFormatException;    public class  UnknownFormatFlagsException  extends IllegalFormatException; public class  InvalidPropertiesFormatException  extends java.io.IOException; public class  MissingResourceException  extends RuntimeException; public class  NoSuchElementException  extends RuntimeException;    public class  InputMismatchException  extends NoSuchElementException; public class  TooManyListenersException  extends Exception;