indexOf.java

    int indexOf(Object key, int hash) {
        ...                                   
        //next available position for our element = 0
        //to show, that we don't have this key, will execute ~0, which is equal -1
        int index = binarySearchHashes(mHashes, N, hash);


        if (index < 0) {
          // hash code not found, "put" operation
            return index;
        }
        ...
    }