public final class CategoryAnchor implements Serializable {

    /** For serialization. */
    private static final long serialVersionUID = -2604142742210173810L;
    
    /** Start of period. */
    public static final CategoryAnchor START 
        = new CategoryAnchor("CategoryAnchor.START");

    /** Middle of period. */
    public static final CategoryAnchor MIDDLE 
        = new CategoryAnchor("CategoryAnchor.MIDDLE");

    /** End of period. */
    public static final CategoryAnchor END 
        = new CategoryAnchor("CategoryAnchor.END");

    /** The name. */
    private String name;

    /**
     * Private constructor.
     *
     * @param name  the name.
     */
    private CategoryAnchor(String name) {
        this.name = name;
    }

    /**
     * Returns a string representing the object.
     *
     * @return The string.
     */
    public String toString() {
        return this.name;
    }

    /**
     * Returns <code>true</code> if this object is equal to the specified 
     * object, and <code>false</code> otherwise.
     *
     * @param obj  the other object.
     *
     * @return A boolean.
     */
    public boolean equals(Object obj) {

        if (this == obj) {
            return true;
        }
        if (!(obj instanceof CategoryAnchor)) {
            return false;
        }
        CategoryAnchor position = (CategoryAnchor) obj;
        if (!this.name.equals(position.toString())) {
            return false;
        }
        return true;

    }
    
    /**
     * Ensures that serialization returns the unique instances.
     * 
     * @return The object.
     * 
     * @throws ObjectStreamException if there is a problem.
     */
    private Object readResolve() throws ObjectStreamException {
        if (this.equals(CategoryAnchor.START)) {
            return CategoryAnchor.START;
        }
        else if (this.equals(CategoryAnchor.MIDDLE)) {
            return CategoryAnchor.MIDDLE;
        }    
        else if (this.equals(CategoryAnchor.END)) {
            return CategoryAnchor.END;
        }    
        return null;