1. 哈希表（散列表）

import java.util.HashMap;
import java.util.Map;


public class Main 
{
    public static void main(String[] args) {
        Map<String, Integer> hash = new HashMap<String, Integer>();
        hash.put("abc", 1);
        hash.put("def", 2);

        System.out.println(hash.get("abc"));
        
        for (String key : hash.keySet())
        {
            System.out.println(key + " : " + hash.get(key));
        }

    }
}