Is there a way to affect a statement that will be used later in Java?

I am not sure how clear the title is. I am working on creating an ArrayList (specifically for Strings) in Java, and I want to merge removeAll() and retainAll() into one method. This is what I have:

@Override
    public boolean removeAll(Collection<?> c) {
        return removeSome(c, true);
    }

    @Override
    public boolean retainAll(Collection<?> c) {
        return removeSome(c, false);
    }

And for the method itself:

private boolean removeSome(Collection<? extends String> c, boolean remove) { //remove vs retain
        collectionIsNullCheck(c);

        if (c.isEmpty()) {
            return false;
        }

        int newInsertionPoint = 0;
        boolean changed = false;

        for (int i = 0; i < insertionPoint; i++) {
            
            if (remove) { //remove
                if (!c.contains(backingStore[i])) {
                    backingStore[newInsertionPoint++] = backingStore[i];
                    
                    //this check is here because maybe backingStore and c don't intersect
                    if (!changed)
                        changed = true;
                }
            } else { //retain
                if (c.contains(backingStore[i])) {
                    backingStore[newInsertionPoint++] = backingStore[i];
                    
                    if (!changed)
                        changed = true;
                }
            }
        }

        Arrays.fill(backingStore, newInsertionPoint, backingStore.length - 1, null);
        insertionPoint = newInsertionPoint;

        return changed;
    }

What I am curious about is whether there is some way to not duplicate the entire code block of

if (!c.contains(backingStore[i])) {
    backingStore[newInsertionPoint++] = backingStore[i];
                    
    //this check is here because maybe backingStore and c don't intersect
    if (!changed)
        changed = true;
}

I considered something like

if ((remove && !c.contains(backingStore[i])) || (!remove && c.contains(backingStore[i]))) {
    ...
}

But I was wondering if there is a better way.