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Mahout-HashMap的进化版FastByIdMap,mahout


FastByIdMap是基于散列的,在处理冲突时是线性探测而非分离链接,这样就不必为每一个条目增加一个Map.Entry对象,从而节省内存开销。
下面代码是一个线性探测Map的Demo:

package com.example.mahout;

public class ArrayHashST_Linear_Probing<Key, Val> {
    private int M = 30001;
    private Key[] keys = (Key[]) new Object[M];
    private Val[] vals = (Val[]) new Object[M];

    private int hash(Key key) {
        return (key.hashCode() & 0x7fffffff) % M;
    }

    public void put(Key key, Val val) {
        int i;
        for (i = hash(key); keys[i] != null; i = (i + 1) % M)
            if (keys[i].equals(key))
                break;
        keys[i] = key;
        vals[i] = val;
    }

    public Val get(Key key) {
        int i;
        for (i = hash(key); keys[i] != null; i = (i + 1) % M)
            if (keys[i].equals(key))
                break;
        return vals[i];
    }

    public static void main(String[] args) {

        ArrayHashST_Linear_Probing<String,String> st = new ArrayHashST_Linear_Probing<String, String>();
        st.put("jocularly", "jocularly");
        st.put("seriously", "seriously");
        st.put("listen", "listen");
        st.put("suburban", "suburban");
        st.put("untravelled", "untravelled");
        st.put("considerating", "considerating");
        st.put("browsing","browsing");
        System.out.println(st.get("jocularly"));




    }

}

这个是分离链接的Demo:

package com.example.mahout;

public class ListHashST_Separate_Chaining<Key, Value> {
    private int M = 8191;
    private Node[] st = new Node[M];

    private static class Node {
        Object key;
        Object val;
        Node next;

        Node(Object key, Object val, Node next) {
            this.key = key;
            this.val = val;
            this.next = next;
        }
    }

    private int hash(Key key) {
        return (key.hashCode() & 0x7fffffff) % M;
    }

    public void put(Key key, Value val) {
        int i = hash(key);
        for (Node x = st[i]; x != null; x = x.next) {
            if (key.equals(x.key)) {
                x.val = val;
                return;
            }
        }
        st[i] = new Node(key, val, st[i]);
    }

    public Value get(Key key) {
        int i = hash(key);
        //System.out.println(i);
        for (Node x = st[i]; x != null; x = x.next){
            System.out.println(x.val);
            if (key.equals(x.key))
                return (Value) x.val;

        }

        return null;
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        ListHashST_Separate_Chaining<String, String> st =  new ListHashST_Separate_Chaining<String, String>();
        st.put("jocularly", "jocularly");
        st.put("seriously", "seriously");
        st.put("listen", "listen");
        st.put("suburban", "suburban");
        st.put("untravelled", "untravelled");
        st.put("considerating", "considerating");
        st.put("browsing","browsing");
        st.get("jocularly");
        //System.out.println(st.get("jocularly"));


    }

}

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