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org.apache.derby.iapi.util
Class JBitSet  

java.lang.Object
  org.apache.derby.iapi.util.JBitSet

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public final class JBitSet

extends java.lang.Object

JBitSet is a wrapper class for BitSet. It is a fixed length implementation which can be extended via the grow() method. It provides additional methods to manipulate BitSets. NOTE: JBitSet was driven by the (current and perceived) needs of the optimizer, but placed in the util package since it is not specific to query trees.. NOTE: java.util.BitSet is final, so we must provide a wrapper class which includes a BitSet member in order to extend the functionality. We want to make it look like JBitSet extends BitSet, so we need to provide wrapper methods for all of BitSet's methods.

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Field Summary
private  java.util.BitSet	bitSet
private  int	size

 

Constructor Summary
private	JBitSet(java.util.BitSet bitSet, int size)           Construct a JBitSet with the specified bitSet.
	JBitSet(int size)           Construct a JBitSet of the specified size.

 

Method Summary
void	and(JBitSet set)
void	clear(int bitIndex)
void	clearAll()           Clear all of the bits in this JBitSet
java.lang.Object	clone()           This method may be called to create a new copy of the Object.
boolean	contains(JBitSet jBitSet)           Test to see if one JBitSet contains another one of the same size.
boolean	equals(java.lang.Object obj)           Determine whether this Object is semantically equal to another Object.
boolean	get(int bitIndex)
int	getFirstSetBit()           Get the first set bit (starting at index 0) from a JBitSet.
void	grow(int newSize)           Grow an existing JBitSet to the specified size.
int	hashCode()           Get a value that represents this Object, as uniquely as possible within the confines of an int.
boolean	hasSingleBitSet()           See of a JBitSet has exactly 1 bit set.
void	or(JBitSet set)
void	set(int bitIndex)
void	setTo(JBitSet sourceBitSet)           Set the BitSet to have the exact same bits set as the parameter's BitSet.
int	size()           Return the size of bitSet
java.lang.String	toString()           Convert this Object to a human-readable String.
void	xor(JBitSet set)

 

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

 

Field Detail

bitSet

private final java.util.BitSet bitSet

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size

private int size

Constructor Detail

JBitSet

public JBitSet(int size)

Construct a JBitSet of the specified size.

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JBitSet

private JBitSet(java.util.BitSet bitSet,
                int size)

Construct a JBitSet with the specified bitSet.

Method Detail

setTo

public void setTo(JBitSet sourceBitSet)

Set the BitSet to have the exact same bits set as the parameter's BitSet.

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contains

public boolean contains(JBitSet jBitSet)

Test to see if one JBitSet contains another one of the same size.

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hasSingleBitSet

public boolean hasSingleBitSet()

See of a JBitSet has exactly 1 bit set.

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getFirstSetBit

public int getFirstSetBit()

Get the first set bit (starting at index 0) from a JBitSet.

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grow

public void grow(int newSize)

Grow an existing JBitSet to the specified size.

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clearAll

public void clearAll()

Clear all of the bits in this JBitSet

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toString

public java.lang.String toString()

Description copied from class: java.lang.Object

Convert this Object to a human-readable String. There are no limits placed on how long this String should be or what it should contain. We suggest you make it as intuitive as possible to be able to place it into System.out.println() 55 and such.

It is typical, but not required, to ensure that this method never completes abruptly with a java.lang.RuntimeException.

This method will be called when performing string concatenation with this object. If the result is null, string concatenation will instead use "null".

The default implementation returns getClass().getName() + "@" + Integer.toHexString(hashCode()).

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equals

public boolean equals(java.lang.Object obj)

Description copied from class: java.lang.Object

Determine whether this Object is semantically equal to another Object.

There are some fairly strict requirements on this method which subclasses must follow:

• It must be transitive. If a.equals(b) and b.equals(c), then a.equals(c) must be true as well.
• It must be symmetric. a.equals(b) and b.equals(a) must have the same value.
• It must be reflexive. a.equals(a) must always be true.
• It must be consistent. Whichever value a.equals(b) returns on the first invocation must be the value returned on all later invocations.
• a.equals(null) must be false.
• It must be consistent with hashCode(). That is, a.equals(b) must imply a.hashCode() == b.hashCode(). The reverse is not true; two objects that are not equal may have the same hashcode, but that has the potential to harm hashing performance.

This is typically overridden to throw a java.lang.ClassCastException if the argument is not comparable to the class performing the comparison, but that is not a requirement. It is legal for a.equals(b) to be true even though a.getClass() != b.getClass(). Also, it is typical to never cause a java.lang.NullPointerException.

In general, the Collections API (java.util) use the equals method rather than the == operator to compare objects. However, java.util.IdentityHashMap is an exception to this rule, for its own good reasons.

The default implementation returns this == o.

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hashCode

public int hashCode()

Description copied from class: java.lang.Object

Get a value that represents this Object, as uniquely as possible within the confines of an int.

There are some requirements on this method which subclasses must follow:

• Semantic equality implies identical hashcodes. In other words, if a.equals(b) is true, then a.hashCode() == b.hashCode() must be as well. However, the reverse is not necessarily true, and two objects may have the same hashcode without being equal.
• It must be consistent. Whichever value o.hashCode() returns on the first invocation must be the value returned on all later invocations as long as the object exists. Notice, however, that the result of hashCode may change between separate executions of a Virtual Machine, because it is not invoked on the same object.

Notice that since hashCode is used in java.util.Hashtable and other hashing classes, a poor implementation will degrade the performance of hashing (so don't blindly implement it as returning a constant!). Also, if calculating the hash is time-consuming, a class may consider caching the results.

The default implementation returns System.identityHashCode(this)

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clone

public java.lang.Object clone()

Description copied from class: java.lang.Object

This method may be called to create a new copy of the Object. The typical behavior is as follows:

• o == o.clone() is false
• o.getClass() == o.clone().getClass() is true
• o.equals(o) is true

However, these are not strict requirements, and may be violated if necessary. Of the three requirements, the last is the most commonly violated, particularly if the subclass does not override Object.equals(Object)>Object.equals(Object) 55 .

If the Object you call clone() on does not implement java.lang.Cloneable (which is a placeholder interface), then a CloneNotSupportedException is thrown. Notice that Object does not implement Cloneable; this method exists as a convenience for subclasses that do.

Object's implementation of clone allocates space for the new Object using the correct class, without calling any constructors, and then fills in all of the new field values with the old field values. Thus, it is a shallow copy. However, subclasses are permitted to make a deep copy.

All array types implement Cloneable, and override this method as follows (it should never fail):

 public Object clone()
 {
   try
     {
       super.clone();
     }
   catch (CloneNotSupportedException e)
     {
       throw new InternalError(e.getMessage());
     }
 }
 

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get

public boolean get(int bitIndex)

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set

public void set(int bitIndex)

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clear

public void clear(int bitIndex)

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and

public void and(JBitSet set)

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or

public void or(JBitSet set)

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xor

public void xor(JBitSet set)

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size

public int size()

Return the size of bitSet

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