No way to cache method results?

Question

hi,
recently I've had quite a few methods in objects that are quite computationally expensive (or I/O expensive), and that the results of consume little memory.
the reaction was to add code like this
import java.util.*;
class A {
   Map arg2result = new HashMap();
   public Object f(Object arg1, String arg2){
      List args = new ArrayList();
      args.add(arg1);
      args.add(arg2);
      if(!arg2result.containsKey(args)){
         Object result;
         ... some work ...
         arg2result.put(args,result);
      return arg2result(args);
}which works great, but having to do this each time you want to cache a method is very tedious!
I've tried using the java.lang.reflect.InvocationProxy to make a proxy that would do this, but now believe its not possible.
The ideal solution might be a new keyword cached?
class A {
   public cached Object f(Object arg1, String arg2){
      Object result;
      ... some work ...
      return result;
}but doing something like
MyObjectType mot1 = new MyObjectType();
MyObjectType mot2 = CacheFactory.cache(mot);would be nice as an alternative. Not having have any class that you want to cache implement an interface of its own method would be a major advantage..
thanks,
asjf

Answer 1

No, you do not need to alter or re-design the classes at all to >conform to any interface. Here's some of what I use, which won't >compile as-is (I just cut out the most relevant parts, that you might >find useful)thanks, I'm getting a ClassCastException with this?
when you say "you do not need to alter or re-design the classes at all to conform to any interface", is this assuming the class already implements at least one interface?
thanks,
asjf
import java.util.*;
import java.lang.reflect.*;
class Fibonacci {
     public int f(int n) {return n<2 ? 1 : f(n-1) + f(n-2);}
public class Cache2 implements InvocationHandler {
     static Map method2arg2result = new HashMap();
     Object o;
     public Cache2(Object o){this.o=o;}
     public static Object wrap(Object o) {
          Class clazz = o.getClass();
          Class[] interfaces = clazz.getInterfaces();
          return Proxy.newProxyInstance(ClassLoader.getSystemClassLoader(), // use SystemClassLoader for now
          interfaces, new Cache2(o));
     public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {          
          if(!method2arg2result.containsKey(method))
               method2arg2result.put(method, new HashMap());
          Map arg2result = (Map) method2arg2result.get(method);
          List realarg = Arrays.asList(args); // array equality is identity equality
          if(!arg2result.containsKey(realarg))
               arg2result.put(realarg, method.invoke(o,args));
          return arg2result.get(realarg);
     public static void main(String [] arg) throws Exception {
          Fibonacci fibonacci = new Fibonacci();
          Object wrapped = wrap(fibonacci);
          System.out.println(wrapped.getClass());
          Fibonacci proxy = (Fibonacci) wrapped;
          time(fibonacci,"Without cache");
          time(proxy,"With cache");
     public static void time(Fibonacci f, String s){
          long time = -System.currentTimeMillis();
          for(int i=0; i<40; i++)
               System.out.print(f.f(i) + (i==39 ? "\n" : ", "));
          System.out.println(s+" "+(time+System.currentTimeMillis())+"\n");
}