Question

Given the following code, how can I iterate over an object of type ProfileCollection?

public class ProfileCollection implements Iterable {         private ArrayList<Profile> m_Profiles;      public Iterator<Profile> iterator() {                 Iterator<Profile> iprof = m_Profiles.iterator();         return iprof;      }      ...      public Profile GetActiveProfile() {         return (Profile)m_Profiles.get(m_ActiveProfile);     } }  public static void main(String[] args) {      m_PC = new ProfileCollection('profiles.xml');       // properly outputs a profile:      System.out.println(m_PC.GetActiveProfile());        // not actually outputting any profiles:      for(Iterator i = m_PC.iterator();i.hasNext();) {         System.out.println(i.next());      }       // how I actually want this to work, but won't even compile:      for(Profile prof: m_PC) {         System.out.println(prof);      } } 

Answer 1

Iterable is a generic interface. A problem you might be having (you haven’t actually said what problem you’re having, if any) is that if you use a generic interface/class without specifying the type argument(s) you can erase the types of unrelated generic types within the class. An example of this is in Non-generic reference to generic class results in non-generic return types.

So I would at least change it to:

public class ProfileCollection implements Iterable<Profile> {      private ArrayList<Profile> m_Profiles;      public Iterator<Profile> iterator() {                 Iterator<Profile> iprof = m_Profiles.iterator();         return iprof;      }      ...      public Profile GetActiveProfile() {         return (Profile)m_Profiles.get(m_ActiveProfile);     } } 

and this should work:

for (Profile profile : m_PC) {     // do stuff } 

Without the type argument on Iterable, the iterator may be reduced to being type Object so only this will work:

for (Object profile : m_PC) {     // do stuff } 

This is a pretty obscure corner case of Java generics.

If not, please provide some more info about what’s going on.