package test3;

/**
 * This class represents an elastic band.  Each elastic band
 * has a length.
 * 
 * @author Franck van Breugel
 */
public class ElasticBand 
{
    private double length;

    /**
     * Initializes this elastic band with the given length.
     * 
     * @param length the length of this elastic band.
     * @pre. length > 0
     */
    private ElasticBand(double length) 
    {
	this.setLength(length);
    }

    /**
     * Returns the length of this elastic band.
     * 
     * @return the length of this elastic band.
     */
    public double getLength() 
    {
	return this.length;
    }

    /**
     * Sets the length of this elastic band to the given length.
     * 
     * @param length the new length of this elastic band.
     * @pre. length > 0
     */
    public void setLength(double length) 
    {
	this.length = length;
    }
    
    /**
     * Returns an elastic band with the given length.
     * 
     * @param length the length of the elastic band.
     * @pre. length > 0
     * @return an elastic band with the given length.
     */
    public static ElasticBand getInstance(double length)
    {
	return new ElasticBand(length);
    }
    
    /**
     * Tests whether this elastic band is the same as the
     * given object.  Two elastic bands are the same if
     * their length differ by less than 0.01.
     * 
     * @param object an object.
     * @return true if this elastic band is the same as the
     * given object, false otherwise.
     */
    public boolean equals(Object object)
    {
	final double EPSILON = 0.01;
	
	boolean equal;
	if (object != null && this.getClass() == object.getClass())
	{
	    ElasticBand other = (ElasticBand) object;
	    equal = Math.abs(this.getLength() - other.getLength()) < EPSILON;
	}
	else
	{
	    equal = false;
	}
	return equal;
    }
    
    /**
     * Stretches the length of this elastic band by the given factor.
     * For example, if the length of this elastic band is 3 and it
     * is stretched by a factor 1.5 then its length becomes 4.5.
     * 
     * @param factor the stretch factor
     * @pre. factor > 0 && factor < 5
     */
    public void stretch(double factor)
    {
	this.setLength(factor * this.getLength());
    }
}