Java数据结构--HashTable(双散列)

/**
 * Created by root on 16-3-11.
 */

import java.lang.Math;

public class QuadraticProbingHashTable<E> {
    private static int DEFAULT_TABLE_SIZE = 11;
    //fields
    private int currentSize;
    private HashEntry[] array;

    // the HashTable's constructor :
    public QuadraticProbingHashTable() {
        this(DEFAULT_TABLE_SIZE);
    }

    public QuadraticProbingHashTable(int currentSize) {
        allocateArray(currentSize);
        makeEmpty();
    }

    //insert
    public void insert(E x) {
        int currentPos = findPos(x);
        if (isActive(currentPos)) {
            return;
        }
        array[currentPos] = new HashEntry(x);
        if (++currentSize > array.length / 2) {
            rehash();
        }

    }

    //remove
    public void remove(E x) {
        int pos = findPos(x);
        if (isActive(pos)) {
            array[pos].isActive = false;
        }
    }

    //rehash()
    private void rehash() {
        HashEntry[] oldArray = this.array;
        allocateArray(nextPrime(oldArray.length * 2));
        currentSize = 0;
        for (int i = 0; i < oldArray.length; i++) {
            if (oldArray[i] != null && oldArray[i].isActive) {
                this.insert((E) oldArray[i].element);
            }
        }
    }


    //isActive:
    public boolean isActive(int Pos) {
        return array[Pos] != null &&
                array[Pos].isActive
                ;
    }


    //int findPos(E x)    recursive
    private int findPos(E x){
        int offset=1;
        int currentPos=myHash(x);
        while(array[currentPos]!=null && !array[currentPos].element.equals(x)){
            currentPos+=offset;
            offset+=2;
            if(currentPos>=array.length){
                currentPos-=array.length;
            }
        }
        return currentPos;
    }

    //void makeEmpty()
    public void makeEmpty() {
        this.currentSize = 0;
        for (int i = 0; i < array.length; i++) {
            array[i] = null;
        }
    }

    //myHash(E x)
    private int myHash(E x) {
        int hashVal = x.hashCode();
        hashVal %= array.length;
        if (hashVal < 0) {
            return hashVal + array.length;
        } else {
            return hashVal;
        }
    }

    //void allocate(int arraySize)
    public void allocateArray(int arraySize) {
        this.array = new HashEntry[nextPrime(arraySize)];
    }

    //int nextPrime(int n)
    private int nextPrime(int n) {
        int sqrt = (int) java.lang.Math.sqrt(n);
        if (isPrime(n, sqrt)) {
            return n;
        } else {
            return nextPrime(n + 1);
        }
    }

    private boolean isPrime(int x, int y) {
        if (y == 1) {
            return true;
        } else if (x % y == 0) {
            return false;
        } else {
            return isPrime(x, y - 1);
        }
    }

    //internal class  constructor : HashEntry(E el,boolean i)
    private static class HashEntry<E> {           //internal class
        public E element;
        public boolean isActive;

        public HashEntry(E element) {
            this(element, true);
        }

        public HashEntry(E el, boolean i) {
            this.element = el;
            this.isActive = i;
        }
    }
}