Switch over type in java

Question

Before I start, I know there are a bunch of answers to this question that suggest alternate approaches. I\'m looking for assistance to this particular approach as to whethe

Answer 1

You was very close to the solution with enums. It hasn't compiled because your enum missed constructor and coversion method to map enum from String. Actually you could solve it even without String, i.e. without calling getCanonicalName at all:

public enum Classes {
  // changed enum constants a bit to avoid confusing with target class names
  ClsA (A.class),
  ClsB (B.class),
  ClsC (C.class),
  UNKNOWN(null);
  private final Class targetClass;
  Classes(Class targetClass) {
    this.targetClass = targetClass;
  }
  public static Classes fromClass(Class cls) {
    for(Classes c : values()) {
      if(c.targetClass == cls)
         return c;
    }
    return UNKNOWN;
  }
}

switch (Classes.fromClass(o.getClass())) {
case ClsA:
  handleA((A)o);
  break;
case ClsB:
  handleB((B)o);
  break;
case ClsC:
  handleC((C)o);
  break;
default:
  handleUnknown(o);
  break;
}

if you get significant count of known classes, consider using map instead of iterating in Classes.fromClass, e.g.:

public enum Classes {
  ClsA(A.class),
  ClsB(B.class),
  // etc...
  UNKNWON(null);

  // need a wrapper class to avoid compilation problem
  // with referring static enum field within an initializer 
  private static class Holder {
    public static final IdentityHashMap, Classes> map = new IdentityHashMap<>();
  }
  Classes(Class targetClass) {
    Holder.map.put(targetClass, this);
  }
  public static Classes fromClass(Class cls) {
    Classes c = Holder.map.get(cls);
    return c != null ? c : UNKNOWN;
  }
}