Hash table with double hashing : HashTable Map « Collections Data Structure « Java
Hash table with double hashing
import java.io.IOException;
public class HashTableWithDoubleHashing {
private DataItem[] hashArray;
private int arraySize;
private DataItem bufItem; // for deleted items
HashTableWithDoubleHashing(int size) {
arraySize = size;
hashArray = new DataItem[arraySize];
bufItem = new DataItem(-1);
}
public void displayTable() {
System.out.print("Table: ");
for (int j = 0; j < arraySize; j++) {
if (hashArray[j] != null)
System.out.print(hashArray[j].getKey() + " ");
else
System.out.print("** ");
}
System.out.println("");
}
public int hashFunc1(int key) {
return key % arraySize;
}
public int hashFunc2(int key) {
return 6 - key % 6;
}
public void insert(int key, DataItem item) {
int hashVal = hashFunc1(key); // hash the key
int stepSize = hashFunc2(key); // get step size
// until empty cell or -1
while (hashArray[hashVal] != null && hashArray[hashVal].getKey() != -1) {
hashVal += stepSize; // add the step
hashVal %= arraySize; // for wraparound
}
hashArray[hashVal] = item; // insert item
}
public DataItem delete(int key) {
int hashVal = hashFunc1(key);
int stepSize = hashFunc2(key); // get step size
while (hashArray[hashVal] != null) {
if (hashArray[hashVal].getKey() == key) {
DataItem temp = hashArray[hashVal]; // save item
hashArray[hashVal] = bufItem; // delete item
return temp; // return item
}
hashVal += stepSize; // add the step
hashVal %= arraySize; // for wraparound
}
return null; // can't find item
}
public DataItem find(int key) {
int hashVal = hashFunc1(key); // hash the key
int stepSize = hashFunc2(key); // get step size
while (hashArray[hashVal] != null) {
if (hashArray[hashVal].getKey() == key)
return hashArray[hashVal]; // yes, return item
hashVal += stepSize; // add the step
hashVal %= arraySize; // for wraparound
}
return null; // can't find item
}
public static void main(String[] args) throws IOException {
int aKey;
DataItem aDataItem;
int size, initSize;
size = 100;
initSize = 10;
HashTableWithDoubleHashing theHashTable = new HashTableWithDoubleHashing(
size);
for (int i = 0; i < initSize; i++) {
aKey = (int) (java.lang.Math.random() * 2 * size);
aDataItem = new DataItem(aKey);
theHashTable.insert(aKey, aDataItem);
}
theHashTable.displayTable();
aKey = 100;
aDataItem = new DataItem(aKey);
theHashTable.insert(aKey, aDataItem);
aKey = 100;
theHashTable.delete(aKey);
aKey = 100;
aDataItem = theHashTable.find(aKey);
if (aDataItem != null)
System.out.println("Found " + aKey);
else
System.out.println("Could not find " + aKey);
}
}
class DataItem {
private int data;
public DataItem(int i) {
data = i;
}
public int getKey() {
return data;
}
}
