Show.java

abstract class Show<A> {
  
  public static register(Class c, Show s){
     Map<Class,Object> shows=TypeClassFactory.tcs.get(Show.class)
     if(shows!=null){
       shows.put(c,s);
     }else{
       shows = new Map<Class,Object>();
       shows.put(c,s);
       TypeClassFactory.tcs.put(Show.class, shows);
     }
  }

  public static show(A a){
    Show<A> tmp=TypeClassFactory.implicitly(Show.class, a);
    tmp.apply(a)
  }

  String apply(A a);
}

ShowInteger.java

public class ShowInteger implements Show<Integer> {
  static{
     Show.register(Integer.class, new ShowInteger());
  }

  @Override
	public String apply(Integer a) {
		return a.toString();
	}

}

ShowList.java

public class ShowList implements Show<List>{
  static{
     Show.register(ArrayList.class, new ShowList());
  }

  @Override
	public String apply(List a) {
		StringBuffer sb = new StringBuffer();
		sb.append("List(");
		for(int i = 0; i < a.size(); i++) {
			sb.append(a.get(i));
			sb.append(", ");
		}
		if(!a.isEmpty()) { 
		  sb.delete(sb.length() - 2, sb.length());
		}
		sb.append(")");
		return sb.toString();
	}
	
}

TypeClassFactory.java

public class TypeClassFactory {
  
	private static final Map<Class, Map<Class, Object>> tcs = new HashMap<Class, Map<Class, Object>>();
	
	
	
	public static <TC, A> TC implicitly(Class typeClass, A fr) {
		return (TC)tcs.get(typeClass).get(fr.getClass());
	}
}

Use.java

public class ImplicitProgram {
  public static void main(String[] args) {
		Integer a = 123;
		List<String> l = new ArrayList<String>();
		l.add("abc");
		l.add("def");
		l.add("ghi");
		

		System.out.println(Show.show(a));
		
		System.out.println(Show.show(a));
	}
}