How to check the java data type of an element in a custom collection?

Question

Object ele=a.get(i);
if(ele instanceof java.lang.Integer){//cast to integer:
    print("found Int");
}else{ //cast to string:
    print("found: "+ele.getClass());
}
//prints: found: class com.cycling74.max.Atom$IntAtom

This is part of a larger chunk of code but this is the relevant part. I need to know how to check the type of an element in the Atom class by cycling74.

if(ele instanceof com.cycling74.max.Atom$IntAtom)
//ERROR: com.cycling74.max.Atom.IntAtom has private access in com.cycling74.max.Atom

Any ideas?? Thanks a lot - this is really doing my head in!!

If the class is declared `private` you can't do an `instanceof` outside of `com.cycling74.max.Atom` class. — Buhake Sindi, Mar 30 '11 at 16:14

Matt Wonlaw · Accepted Answer · 2011-03-30T16:31:48.823

Yes, it is possible without making IntAtom public although it is a bit hacky.

First you need to get a reference to the private inner IntAtom class:

public class SomeClass {
  public static final Class<?> INT_ATOM_CLASS;
  static {
    Class<?> [] innerClasses = Atom.class.getDeclaredClasses();
    Class<?> intAtomClass = null;
    for (Class<?> klass : innerClasses) {
      if (klass.getSimpleName().equals("IntAtom")) {
        intAtomClass = klass;
        break;
      }
    }
    INT_ATOM_CLASS = intAtomClass;
  }
}

Then to do the instanceof check:

if (SomeClass.INT_ATOM_CLASS.isAssignableFrom(ele.getClass())) {
   // do stuff
}

Javadoc for Class.isAssignableFrom(Class c);

score 1 · Answer 2 · answered Mar 30 '11 at 16:12

1

I think you'll have to either make IntAtom public, or provide a public function in Atom that can verify whether an object is an IntAtom or not. Right now the class definition can't be compared against because it's private to Atom.

answered Mar 30 '11 at 16:12

roberttdev

42,762
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Hmm, thanks @roberttdev It sounds complicated. I dont have access to the Atom class tho. It's an API built into MaxMSP software. Also, if I did have access,I wouldnt know where to begin doing that as I'm brand new to java! (this is my first project!). Is there any hacky workaround I might be able to try?? – cronoklee Mar 30 '11 at 16:16
The only thing I can think of is to subclass Atom and make the change yourself. It's not pretty.. but I don't know how else you can access that private class. Double check the API to make sure they don't offer something for this first. – roberttdev Mar 30 '11 at 16:20
your subclassing solution won't help as private classes isn't inherited by the subclasses. – Buhake Sindi Mar 30 '11 at 16:22
it is *possible* to do it without making IntAtom public, although not necessarily advisable. See my answer below. – Matt Wonlaw Mar 30 '11 at 16:34

score 0 · Answer 3 · answered Mar 30 '11 at 16:27

0

Thanks a lot fellas - it seems the Atom class has a method somewhere called isInt() that can check the built in datatype. I wouldnt have looked for it had you guys not got back so I really appreciate the help!

answered Mar 30 '11 at 16:27

cronoklee

6,482
9
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This should have been a comment, i.e. don't post comments on answer sections. – Buhake Sindi Mar 30 '11 at 17:21

How to check the java data type of an element in a custom collection?

3 Answers3