A hash map with int key and int values. : Hash Code « Development Class « Java
A hash map with int key and int values.
/*
* Copyright 2004-2011 H2 Group. Multiple-Licensed under the H2 License,
* Version 1.0, and under the Eclipse Public License, Version 1.0
* (http://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
//package org.h2.util;
/*
* Copyright 2004-2011 H2 Group. Multiple-Licensed under the H2 License,
* Version 1.0, and under the Eclipse Public License, Version 1.0
* (http://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
//package org.h2.util;
/**
* A hash map with int key and int values. There is a restriction: the
* value -1 (NOT_FOUND) cannot be stored in the map. 0 can be stored.
* An empty record has key=0 and value=0.
* A deleted record has key=0 and value=DELETED
*/
public class IntIntHashMap extends HashBase {
/**
* The value indicating that the entry has not been found.
*/
public static final int NOT_FOUND = -1;
private static final int DELETED = 1;
private int[] keys;
private int[] values;
private int zeroValue;
protected void reset(int newLevel) {
super.reset(newLevel);
keys = new int[len];
values = new int[len];
}
/**
* Store the given key-value pair. The value is overwritten or added.
*
* @param key the key
* @param value the value (-1 is not supported)
*/
public void put(int key, int value) {
if (key == 0) {
zeroKey = true;
zeroValue = value;
return;
}
try {
checkSizePut();
} catch (Exception e) {
// in fact, it is never thrown
// TODO hash: maybe optimize it
}
int index = getIndex(key);
int plus = 1;
int deleted = -1;
do {
int k = keys[index];
if (k == 0) {
if (values[index] != DELETED) {
// found an empty record
if (deleted >= 0) {
index = deleted;
deletedCount--;
}
size++;
keys[index] = key;
values[index] = value;
return;
}
// found a deleted record
if (deleted < 0) {
deleted = index;
}
} else if (k == key) {
// update existing
values[index] = value;
return;
}
index = (index + plus++) & mask;
} while(plus <= len);
}
/**
* Remove the key-value pair with the given key.
*
* @param key the key
*/
public void remove(int key) {
if (key == 0) {
zeroKey = false;
return;
}
try {
checkSizeRemove();
} catch (Exception e) {
// in fact, it is never thrown
// TODO hash: maybe optimize it
}
int index = getIndex(key);
int plus = 1;
do {
int k = keys[index];
if (k == key) {
// found the record
keys[index] = 0;
values[index] = DELETED;
deletedCount++;
size--;
return;
} else if (k == 0 && values[index] == 0) {
// found an empty record
return;
}
index = (index + plus++) & mask;
} while(plus <= len);
// not found
}
protected void rehash(int newLevel) {
int[] oldKeys = keys;
int[] oldValues = values;
reset(newLevel);
for (int i = 0; i < oldKeys.length; i++) {
int k = oldKeys[i];
if (k != 0) {
put(k, oldValues[i]);
}
}
}
/**
* Get the value for the given key. This method returns NOT_FOUND if the
* entry has not been found.
*
* @param key the key
* @return the value or NOT_FOUND
*/
public int get(int key) {
if (key == 0) {
return zeroKey ? zeroValue : NOT_FOUND;
}
int index = getIndex(key);
int plus = 1;
do {
int k = keys[index];
if (k == 0 && values[index] == 0) {
// found an empty record
return NOT_FOUND;
} else if (k == key) {
// found it
return values[index];
}
index = (index + plus++) & mask;
} while(plus <= len);
return NOT_FOUND;
}
}
/**
* The base for other hash classes.
*/
abstract class HashBase {
private static final int MAX_LOAD = 90;
/**
* The bit mask to get the index from the hash code.
*/
protected int mask;
/**
* The number of slots in the table.
*/
protected int len;
/**
* The number of occupied slots, excluding the zero key (if any).
*/
protected int size;
/**
* The number of deleted slots.
*/
protected int deletedCount;
/**
* The level. The number of slots is 2 ^ level.
*/
protected int level;
/**
* Whether the zero key is used.
*/
protected boolean zeroKey;
private int maxSize, minSize, maxDeleted;
public HashBase() {
reset(2);
}
/**
* Increase the size of the underlying table and re-distribute the elements.
*
* @param newLevel the new level
*/
protected abstract void rehash(int newLevel);
/**
* Get the size of the map.
*
* @return the size
*/
public int size() {
return size + (zeroKey ? 1 : 0);
}
/**
* Check the size before adding an entry. This method resizes the map if
* required.
*/
void checkSizePut() {
if (deletedCount > size) {
rehash(level);
}
if (size + deletedCount >= maxSize) {
rehash(level + 1);
}
}
/**
* Check the size before removing an entry. This method resizes the map if
* required.
*/
protected void checkSizeRemove() {
if (size < minSize && level > 0) {
rehash(level - 1);
} else if (deletedCount > maxDeleted) {
rehash(level);
}
}
/**
* Clear the map and reset the level to the specified value.
*
* @param newLevel the new level
*/
protected void reset(int newLevel) {
minSize = size * 3 / 4;
size = 0;
level = newLevel;
len = 2 << level;
mask = len - 1;
maxSize = (int) (len * MAX_LOAD / 100L);
deletedCount = 0;
maxDeleted = 20 + len / 2;
}
/**
* Calculate the index for this hash code.
*
* @param hash the hash code
* @return the index
*/
protected int getIndex(int hash) {
return hash & mask;
}
}
