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Asked: 2026-05-11T00:53:42+00:00

private HashMap<DataObject, HashSet> AllDataObjects; … /** Returns all DataObject elements that are NOT in

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private HashMap<DataObject, HashSet> AllDataObjects;  ...  /** Returns all DataObject elements that are NOT in the specified set. */ private DataObject[] invert( HashSet<DataObject> set ) {     HashSet<DataObject> keys = (HashSet) AllDataObjects.keySet();     keys = (HashSet) keys.clone();      keys.removeAll( set );      return (DataObject[]) keys.toArray(); }

Note that I don’t want to alter AllDataObjects through this process. I casted the set of AllDataObjects‘ keys (which are the DataObjects I want the set parameter to subtract from) into a HashSet to use clone, which supposedly returns a shallow copy that I can then remove set from without affecting AllDataObjects.

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1 Answer

  1. Create a new set and give the one to be cloned as an argument. This avoids casting and so you don’t lose generics.

    private DataObject[] invert( Set<DataObject> set ){     Set<DataObject> keys = new HashSet<DataObject>(AllDataObjects.keySet());     keys.removeAll( set );     return keys.toArray(new DataObject[]{}); }

    It’s also worth noting that you should use Set rather than HashSet for the parameter so as to not overly burden your clients.

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