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Chapter 17 |  |
17. The java.util Package
Contents:
Calendar
Date
Dictionary
EmptyStackException
Enumeration
EventListener
EventObject
GregorianCalendar
Hashtable
ListResourceBundle
Locale
MissingResourceException
NoSuchElementException
Observable
Observer
Properties
PropertyResourceBundle
Random
ResourceBundle
SimpleTimeZone
Stack
StringTokenizer
TimeZone
TooManyListenersException
Vector
The package java.util contains a number of useful classes and interfaces. Although the name of the package might imply that these are utility classes, they are really more important than that. In fact, Java depends directly on several of the classes in this package, and many programs will find these classes indispensable. The classes and interfaces in java.util include:
- The Hashtable class for implementing hashtables,
or associative arrays.
- The Vector class, which supports
variable-length arrays.
- The Enumeration interface for iterating through
a collection of elements.
- The StringTokenizer class for
parsing strings into distinct tokens separated by
delimiter characters.
- The EventObject class and the
EventListener interface, which form the basis of the
new AWT event model in Java 1.1.
- The Locale class in Java 1.1, which represents
a particular locale for internationalization purposes.
- The Calendar and TimeZone
classes in Java. These classes interpret
the value of a Date
object in the context of a particular calendar system.
- The ResourceBundle class and its subclasses,
ListResourceBundle and
PropertyResourceBundle, which represent
sets of localized data in Java 1.1.
Figure 17.1 shows the class hierarchy for the java.util package.
![[Graphic: Figure 17-1]](./figs/jfc_1701.gif)
BitSet
Name
BitSetSynopsis
- Class Name:
-
java.util.BitSet
- Superclass:
-
java.lang.Object
- Immediate Subclasses:
-
None
- Interfaces Implemented:
-
java.lang.Cloneable, java.io.Serializable
- Availability:
-
JDK 1.0 or later
Description
The BitSet class implements a set of bits. The set grows in size as needed. Each element of a BitSet has a boolean value. When a BitSet object is created, all of the bits are set to false by default. The bits in a BitSet are indexed by nonnegative integers, starting at 0. The size of a BitSet is the number of bits that it currently contains. The BitSet class provides methods to set, clear, and retrieve the values of the individual bits in a BitSet. There are also methods to perform logical AND, OR, and XOR operations.
Class Summary
public final class java.util.BitSet extends java.lang.Object
implements java.lang.Cloneable, java.io.Serializable {
// Constructors
public BitSet();
public BitSet(int nbits);
// Instance Methods
public void and(BitSet set);
public void clear(int bit);
public Object clone();
public boolean equals(Object obj);
public boolean get(int bit);
public int hashCode();
public void or(BitSet set);
public void set(int bit);
public int size();
public String toString();
public void xor(BitSet set);
}
Constructors
BitSet
public BitSet()
- Description
-
This constructor creates a BitSet with a default size of 64 bits. All of the bits in the BitSet are initially set to false.
public BitSet(int nbits)
- Parameters
-
- nbits
-
The initial number of bits.
- nbits
- Description
-
This constructor creates a BitSet with a size of nbits. All of the bits in the BitSet are initially set to false.
Instance Methods
and
public void and(BitSet set)
- Parameters
-
- set
-
The BitSet to AND with this BitSet.
- set
- Description
-
This method computes the logical AND of this BitSet and the specified BitSet and stores the result in this BitSet. In other words, for each bit in this BitSet, the value is set to only true if the bit is already true in this BitSet and the corresponding bit in set is true.
If the size of set is greater than the size of this BitSet, the extra bits in set are ignored. If the size of set is less than the size of this BitSet, the extra bits in this BitSet are set to false.
clear
public void clear(int bit)
- Parameters
-
- bit
-
The index of the bit to clear.
- bit
- Description
-
This method sets the bit at the given index to false. If bit is greater than or equal to the number of bits in the BitSet, the size of the BitSet is increased so that it contains bit values. All of the additional bits are set to false.
clone
public Object clone()
- Returns
-
A copy of this BitSet.
- Overrides
-
Object.clone()
- Description
-
This method creates a copy of this BitSet and returns it. In other words, the returned BitSet has the same size as this BitSet, and it has the same bits set to true.
equals
public boolean equals(Object obj)
- Parameters
-
- obj
-
The object to be compared with this object.
- obj
- Returns
-
true if the objects are equal; false if they are not.
- Overrides
-
Object.equals()
- Description
-
This method returns true if obj is an instance of BitSet and it contains the same bit values as the object this method is associated with. In other words, this method compares each bit of this BitSet with the corresponding bit of obj. If any bits do not match, the method returns false. If the size of this BitSet is different than obj, the extra bits in either this BitSet or in obj must be false for this method to return true.
get
public boolean get(int bit)
- Parameters
-
- bit
-
The index of the bit to retrieve.
- bit
- Returns
-
The boolean value of the bit at the given index.
- Description
-
This method returns the value of the given bit. If bit is greater than or equal to the number of bits in the BitSet, the method returns false.
hashCode
public int hashCode()
- Returns
-
The hashcode for this BitSet.
- Overrides
-
Object.hashCode()
- Description
-
This method returns a hashcode for this object.
or
public void or(BitSet set)
- Parameters
-
- set
-
The BitSet to OR with this BitSet.
- set
- Description
-
This method computes the logical OR of this BitSet and the specified BitSet, and stores the result in this BitSet. In other words, for each bit in this BitSet, the value is set to true if the bit is already true in this BitSet or the corresponding bit in set is true.
If the size of set is greater than the size of this BitSet, this BitSet is first increased in size to accommodate the additional bits. All of the additional bits are initially set to false.
set
public void set(int bit)
- Parameters
-
- bit
-
The index of the bit to set.
- bit
- Description
-
This method sets the bit at the given index to true. If bit is greater than or equal to the number of bits in the BitSet, the size of the BitSet is increased so that it contains bit values. All of the additional bits except the last one are set to false.
size
public int size()
- Returns
-
The size of this BitSet.
- Description
-
This method returns the size of this BitSet, which is the number of bits currently in the set.
toString
public String toString()
- Returns
-
A string representation of this BitSet.
- Overrides
-
Object.toString()
- Description
-
This method returns a string representation of this BitSet. The string lists the indexes of all the bits in the BitSet that are true.
xor
public void xor(BitSet set)
- Parameters
-
- set
-
The BitSet to XOR with this BitSet.
- set
- Description
-
This method computes the logical XOR (exclusive OR) of this BitSet and the specified BitSet and stores the result in this BitSet. In other words, for each bit in this BitSet, the value is set to true only if the bit is already true in this BitSet, and the corresponding bit in set is false, or if the bit is false in this BitSet and the corresponding bit in set is true.
If the size of set is greater than the size of this BitSet, this BitSet is first increased in size to accommodate the additional bits. All of the additional bits are initially set to false.
Inherited Methods
|
Method |
Inherited From |
Method |
Inherited From |
|---|---|---|---|
|
finalize() |
Object |
getClass() |
Object |
|
notify() |
Object |
notifyAll() |
Object |
|
wait() |
Object |
wait(long) |
Object |
|
wait(long, int) |
Object |
See Also
Cloneable, Serializable
|
 |
|
| Vector |  |
Calendar |
