Question

Is there a more efficient/quicker/more sensible to copy part of an ArrayList than the way I’m doing it?

 public ArrayList<FooObject> getListOfFlagged() {    
        for(FooObject fooObject: foos) {
            //for each item in the original array, where the item isFlagged...
            if(fooObject.isFlagged) {
                someOtherArray.add(fooObject);
            }
        }    
        return someOtherArray;
    }

Answer 1

You can use Collections2.filter() method from guava. It’ll look more functionally:

    Collections2.filter(foos, new Predicate<FooObject>() {
        @Override
        public boolean apply(FooObject input) {
            return fooObject.isFlagged();
        }
    })

The result is backed by your original foos collection, so if you need a copy, then you have to make a defensive copy with new ArrayList<FooObject>(filteredCollection).