public int indexOf(Object key) {
        return key == null ? indexOfNull() : indexOf(key, key.hashCode());
    }
Returns the index of a value in the set.

@param key The value to search for.
@return Returns the index of the value if it exists, else a negative integer.
replugin-host-library/replugin-host-lib/src/main/java/com/qihoo360/replugin/utils/basic/ArraySet.java