Is there a tool or library to find duplicate entries in a Collection according to specific criteria that can be implemented?
To make myself clear: I want to compare the entries to each other according to specific criteria. So I think a Predicate returning just true or false isn't enough.
I can't use equals.
If you want to find duplicates, rather than just removing them, one approach would be to throw the Collection into an array, sort the array via a Comparator that implements your criteria, then linearly walk through the array, looking for adjacent duplicates.
Here's a sketch (not tested):
MyComparator myComparator = new MyComparator();
MyType[] myArray = myList.toArray();
Arrays.sort( myArray, myComparator );
for ( int i = 1; i < myArray.length; ++i ) {
if ( 0 == myComparator.compare( myArray[i - 1], myArray[i] )) {
// Found a duplicate!
}
}
Edit: From your comment, you just want to know if there are duplicates. The approach above works for this too. But you could more simply just create a java.util.SortedSet with a custom Comparator. Here's a sketch:
MyComparator myComparator = new MyComparator();
TreeSet treeSet = new TreeSet( myComparator );
treeSet.addAll( myCollection );
boolean containsDuplicates = (treeSet.size() != myCollection.size());