package cal;

public class Addition extends Operator {

	public Addition() {
		super("+");
	}

	@Override
	public double calculate(double val1, double val2) {
		return val1 + val2;
	}
}

package cal;
/**
 * 
 * This is a concrete
 * class that is used 
 * to representing 
 * a Addition object
 * which is extending the
 * abstract operator class
 * 
 * @author cal
 *
 */
public class Addition extends Operator {
	/**
	 * 
	 *  A constructor to 
	 *  initialize the attributes 
	 *  using symbol + as Addition
	 *  
	 */
	public Addition() {
		super("+");
	}

	/**
	 * 
	 *  A method accepting 2 double value
	 *  to calculate and return the Addition 
	 *  value
	 *  @param val1
	 *  @param val2
	 *  
	 */
	@Override
	public double calculate(double val1, double val2) {
		return val1 + val2;
	}
}

Add java doc to Addition class