What is the best way to filter a Java Collection?

Question

I want to filter a java.util.Collection based on a predicate.

Answer 1

"Best" way is too wide a request. Is it "shortest"? "Fastest"? "Readable"? Filter in place or into another collection?

Simplest (but not most readable) way is to iterate it and use Iterator.remove() method:

Iterator it = col.iterator();
while( it.hasNext() ) {
  Foo foo = it.next();
  if( !condition(foo) ) it.remove();
}

Now, to make it more readable, you can wrap it into a utility method. Then invent a IPredicate interface, create an anonymous implementation of that interface and do something like:

CollectionUtils.filterInPlace(col,
  new IPredicate(){
    public boolean keepIt(Foo foo) {
      return foo.isBar();
    }
  });

where filterInPlace() iterate the collection and calls Predicate.keepIt() to learn if the instance to be kept in the collection.

I don't really see a justification for bringing in a third-party library just for this task.