Method add

lib/java/util/HashSet.java:90–93

Adds the specified object to this HashSet if not already present. @param object the object to add. @return true when this HashSet did not already contain the object, false otherwise

(E object)

     *         the object, {@code false} otherwise
     */
    @Override
    public boolean add(E object) {
        return backingMap.put(object, this) == null;
    }

    /**
     * Removes all elements from this {@code HashSet}, leaving it empty.