Java 散列表的实现

摘自http://www.cxybl.com/html/suanfa/201110125445.html

有改动

public class MyHashtable {
    //表中元素个数
    private int manyItems;

    private Object[] keys;
    private Object[] data;

    //若索引i处存在元素，则hasBeenUsed[i]为true，否则为false
    private boolean[] hasBeenUsed;

    //构造函数
    public MyHashtable(int capacity){
        if(capacity <= 0){
            throw new IllegalArgumentException("capacity is negative!");
        }
        keys = new Object[capacity];
        data = new Object[capacity];
        hasBeenUsed = new boolean[capacity];
    }

    //hash函数
    private int hash(Object key){
        return Math.abs(key.hashCode()%data.length);
    }

    //当前索引发生冲突，找下一索引
    private int nextIndex(int i){
        if(i + 1 == data.length){
            return 0;
        }else{
            return i + 1;
        }
    }

    /*
     * 如果在表中找到指定的关键字，返回值为关键字的索引，否则返回-1
     * 也就是说如果已经存在某个键时，返回的是该键的索引，如果没有这个键，则返回-1
     * 在插入新的键时都返回-1
     */
    private int findIndex(Object key){
        int count = 0;
        int i = hash(key);
        System.out.println(i);
        while((count<data.length)&&hasBeenUsed[i]){
            if(key.equals(keys[i])){
                return i;
            }else{
                count++;
                i = nextIndex(i);
            }
        }
        return -1;

    }

    /*
     * 获取某个元素
     */
    public Object get(Object key){
        int index = findIndex(key);
        if(index == -1){
            return null;
        }
        else{
            return data[index];
        }
    }

    /*
     * 放入某个元素
     */
    public Object put(Object key,Object element){
        int index = findIndex(key);
        Object answer;

        //判断索引是不是-1
        if(index != -1){
            answer = data[index];
            data[index] = element;
            return answer;
        }else if(manyItems<data.length){
            index = hash(key);
            while(keys[index] != null){
                index = nextIndex(index);
            }
            keys[index] = key;
            data[index] = element;
            hasBeenUsed[index] = true;
            manyItems++;
            return null;

        }else{
            throw new IllegalStateException("Hsahtable is full");
        }
    }

    /*
     * 删除某个元素
     */
    public Object remove(Object key){
        int index = findIndex(key);
        Object answer = null;
        if(index != -1){
            answer = data[index];
            data[index] = null;
            keys[index] = null;
            manyItems--;
        }
        return answer;
    }

    /*
     * 是否包含某键
     */
    public boolean contains(Object key){
        return (findIndex(key)!=-1);
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        MyHashtable table = new MyHashtable(3);

        table.put(1, "中国");
        Object ob1 = table.put(2, "美国");
        table.put(3, "安徽");

        System.out.println(table.get(2).toString());
        System.out.println(ob1);
    }

}