THash

java.lang.Object
- gnu.trove.THash

All Implemented Interfaces:

java.lang.Cloneable

Direct Known Subclasses:

TObjectHash, TPrimitiveHash
```
public abstract class THash
extends java.lang.Object
implements java.lang.Cloneable
```
Base class for hashtables that use open addressing to resolve collisions. Created: Wed Nov 28 21:11:16 2001

Version:

$Id: THash.java,v 1.6 2002/09/25 05:43:04 ericdf Exp $

Author:

Eric D. Friedman

Field Summary

Fields
Modifier and Type	Field and Description
`protected int`	`_free` the current number of free slots in the hash.
`protected float`	`_loadFactor` Determines how full the internal table can become before rehashing is required.
`protected int`	`_maxSize` The maximum number of elements allowed without allocating more space.
`protected int`	`_size` the current number of occupied slots in the hash.
`protected static int`	`DEFAULT_INITIAL_CAPACITY` the default initial capacity for the hash table.
`protected static float`	`DEFAULT_LOAD_FACTOR` the load above which rehashing occurs.

Constructor Summary

Constructors
Constructor and Description
`THash()` Creates a new `THash` instance with the default capacity and load factor.
`THash(int initialCapacity)` Creates a new `THash` instance with a prime capacity at or near the specified capacity and with the default load factor.
`THash(int initialCapacity, float loadFactor)` Creates a new `THash` instance with a prime capacity at or near the minimum needed to hold `initialCapacity` elements with load factor `loadFactor` without triggering a rehash.

Method Summary

Methods
Modifier and Type	Method and Description
`protected abstract int`	`capacity()`
`void`	`clear()` Empties the collection.
`java.lang.Object`	`clone()`
`void`	`compact()` Compresses the hashtable to the minimum prime size (as defined by PrimeFinder) that will hold all of the elements currently in the table.
`private void`	`computeMaxSize(int capacity)` Computes the values of maxSize.
`void`	`ensureCapacity(int desiredCapacity)` Ensure that this hashtable has sufficient capacity to hold `desiredCapacity additional elements without requiring a rehash.`
`boolean`	`isEmpty()` Tells whether this set is currently holding any elements.
`protected void`	`postInsertHook(boolean usedFreeSlot)` After an insert, this hook is called to adjust the size/free values of the set and to perform rehashing if necessary.
`protected abstract void`	`rehash(int newCapacity)` Rehashes the set.
`protected void`	`removeAt(int index)` Delete the record at `index`.
`protected int`	`setUp(int initialCapacity)` initializes the hashtable to a prime capacity which is at least `initialCapacity + 1`.
`int`	`size()` Returns the number of distinct elements in this collection.
`void`	`trimToSize()` This simply calls `compact`.

Methods inherited from class java.lang.Object
equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - _size
```
protected transient int _size
```
    the current number of occupied slots in the hash.
  - _free
```
protected transient int _free
```
    the current number of free slots in the hash.
  - DEFAULT_LOAD_FACTOR
```
protected static final float DEFAULT_LOAD_FACTOR
```
    the load above which rehashing occurs.
    
    See Also:
    Constant Field Values
  - DEFAULT_INITIAL_CAPACITY
```
protected static final int DEFAULT_INITIAL_CAPACITY
```
    the default initial capacity for the hash table. This is one less than a prime value because one is added to it when searching for a prime capacity to account for the free slot required by open addressing. Thus, the real default capacity is 11.
    
    See Also:
    Constant Field Values
  - _loadFactor
```
protected float _loadFactor
```
    Determines how full the internal table can become before rehashing is required. This must be a value in the range: 0.0 < loadFactor < 1.0. The default value is 0.5, which is about as large as you can get in open addressing without hurting performance. Cf. Knuth, Volume 3., Chapter 6.
  - _maxSize
```
protected int _maxSize
```
    The maximum number of elements allowed without allocating more space.
- Constructor Detail
  - THash
```
public THash()
```
    Creates a new THash instance with the default capacity and load factor.
  - THash
```
public THash(int initialCapacity)
```
    Creates a new THash instance with a prime capacity at or near the specified capacity and with the default load factor.
    
    Parameters:
    initialCapacity - an int value
  - THash
```
public THash(int initialCapacity,
     float loadFactor)
```
    Creates a new THash instance with a prime capacity at or near the minimum needed to hold initialCapacity elements with load factor loadFactor without triggering a rehash.
    
    Parameters:
    initialCapacity - an int value
    loadFactor - a float value
- Method Detail
  - clone
```
public java.lang.Object clone()
```
    Overrides:
    
    clone in class java.lang.Object
  - isEmpty
```
public boolean isEmpty()
```
    Tells whether this set is currently holding any elements.
    
    Returns:
    a boolean value
  - size
```
public int size()
```
    Returns the number of distinct elements in this collection.
    
    Returns:
    an int value
  - capacity
```
protected abstract int capacity()
```
    Returns:
    the current physical capacity of the hash table.
  - ensureCapacity
```
public void ensureCapacity(int desiredCapacity)
```
    Ensure that this hashtable has sufficient capacity to hold desiredCapacity additional elements without requiring a rehash. This is a tuning method you can call before doing a large insert.
    Parameters: desiredCapacity - an int value
  compact public void compact() Compresses the hashtable to the minimum prime size (as defined by PrimeFinder) that will hold all of the elements currently in the table. If you have done a lot of remove operations and plan to do a lot of queries or insertions or iteration, it is a good idea to invoke this method. Doing so will accomplish two things: You'll free memory allocated to the table but no longer needed because of the remove()s. You'll get better query/insert/iterator performance because there won't be any REMOVED slots to skip over when probing for indices in the table. trimToSize public final void trimToSize() This simply calls compact. It is included for symmetry with other collection classes. Note that the name of this method is somewhat misleading (which is why we prefer compact) as the load factor may require capacity above and beyond the size of this collection. See Also: compact() removeAt protected void removeAt(int index) Delete the record at index. Reduces the size of the collection by one. Parameters: index - an int value clear public void clear() Empties the collection. setUp protected int setUp(int initialCapacity) initializes the hashtable to a prime capacity which is at least initialCapacity + 1. Parameters: initialCapacity - an int value Returns: the actual capacity chosen rehash protected abstract void rehash(int newCapacity) Rehashes the set. Parameters: newCapacity - an int value computeMaxSize private final void computeMaxSize(int capacity) Computes the values of maxSize. There will always be at least one free slot required. Parameters: capacity - an int value postInsertHook protected final void postInsertHook(boolean usedFreeSlot) After an insert, this hook is called to adjust the size/free values of the set and to perform rehashing if necessary.

Class THash

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

_size

_free

DEFAULT_LOAD_FACTOR

DEFAULT_INITIAL_CAPACITY

_loadFactor

_maxSize

Constructor Detail

THash

THash

THash

Method Detail

clone

isEmpty

size

capacity

ensureCapacity

compact

trimToSize

removeAt

clear

setUp

rehash

computeMaxSize

postInsertHook