海量数据 统计

import java.util.BitSet; 
 
public class BloomFilter  
{ 
    /*  BitSet初始分配2^24个bit  */  
    private static final int DEFAULT_SIZE = 1 << 25;  
    /* 不同哈希函数的种子，一般应取质数 */ 
    private static final int[] seeds = new int[] { 5, 7, 11, 13, 31, 37, 61 }; 
    private BitSet bits = new BitSet(DEFAULT_SIZE); 
    /* 哈希函数对象 */  
    private SimpleHash[] func = new SimpleHash[seeds.length]; 
 
    public BloomFilter()  
    { 
        for (int i = 0; i < seeds.length; i++) 
        { 
            func[i] = new SimpleHash(DEFAULT_SIZE, seeds[i]); 
        } 
    } 
 
    // 将字符串标记到bits中 
    public void add(String value)  
    { 
        for (SimpleHash f : func)  
        { 
            bits.set(f.hash(value), true); 
        } 
    } 
 
    //判断字符串是否已经被bits标记 
    public boolean contains(String value)  
    { 
        if (value == null)  
        { 
            return false; 
        } 
        boolean ret = true; 
        for (SimpleHash f : func)  
        { 
            ret = ret && bits.get(f.hash(value)); 
        } 
        return ret; 
    } 
 
    /* 哈希函数类 */ 
    public static class SimpleHash  
    { 
        private int cap; 
        private int seed; 
 
        public SimpleHash(int cap, int seed)  
        { 
            this.cap = cap; 
            this.seed = seed; 
        } 
 
        //hash函数，采用简单的加权和hash 
        public int hash(String value)  
        { 
            int result = 0; 
            int len = value.length(); 
            for (int i = 0; i < len; i++)  
            { 
                result = seed * result + value.charAt(i); 
            } 
            return (cap - 1) & result; 
        } 
    } 
} 



参考：

http://blog.csdn.net/lmh12506/article/details/7575651
http://blog.csdn.net/dandingyy/article/details/7408058