Javaにおける異種コンテナの実装(Effective Java 2ndから) ref: http://qiita.com/items/2488

file0.java

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

public class Test
{

    private Map<Class<?>, Object> contents = new HashMap<Class<?>, Object>();
    private <T> T getContent(Class<T> type){

        return  type.cast(contents.get(type));
    }

    public static void main(String[] args)
    {

        Test test = new Test();

        test.contents.put(String.class, "メモですよ");


        String newMemo = test.getContent(String.class);
        System.out.println(newMemo);

    }
}