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FractionInterface file:
/* This file specifies methods for FractionInterface	*/
/* Do not modify this file!!                  			*/

package PJ1;

public interface FractionInterface 
{
        /** Task: Sets this fraction to the given values. 
	 *        Do not reduce and moveMinusSign the fraction object.
         *  @param num is the integer numerator
         *  @param den is the integer denominator
         *  @throw FractionException if denominator is 0  */
        public void setFraction(int num, int den);

        /** Task: Simplify this fraction.
	 *       change the fraction so that the minus sign is indicated by numerator.
         *       then, reduce this fraction to lowest term, i.e divide the numerator
         *       and denominator by their Greatest Common Divisor 
	 *       exmaple: -6/-10 --> 3/5  6/-10 --> -3/5
	 * @return this fraction object */
        public FractionInterface simplify();

	/** Task: return this fraction in double value
	 *  @return the double floating point value of a fraction */
	public double toDouble();

	/** Task: Adds two fractions. 
	 *  @param secondFraction is a fraction that is the second operand of the addition
	 *  @return a new simplify fraction which is the sum of this fraction and 
	 *          the secondFraction. */
	public FractionInterface add(FractionInterface secondFraction);

	/** Task: Subtracts two fractions.
	 *  @param secondFraction a fraction that is the second operand of the subtraction
	 *  @return a new simplify fraction which is the difference of this fraction and 
	 *          the second operand  */
	public FractionInterface subtract(FractionInterface secondFraction);

	/** Task: Multiplies two fractions.
	 *  @param secondFraction a fraction that is the second operand of the multiplication
	 *  @return a new simplify fraction which is the product of this fraction and 
	 *          the second operand  */
	public FractionInterface multiply(FractionInterface secondFraction);

	/** Task: Divides two fractions.
	 *  @param secondFraction a fraction that is the second operand of the division
	 *  @return a new simplify fraction which is the quotient of this fraction and 
	 *          the second operand  
         *  @throw FractionException if secondFraction is 0 */
	public FractionInterface divide(FractionInterface secondFraction);

}