Finishing Rational Class.

src/main/java/Rational/Rational.java

@@ -54,27 +54,27 @@ public class Rational {
     // TODO: Instance method - this - other
     // Formula: a/b - c/d = (a*d - c*b) / (b*d)
     public Rational subtract(Rational other) {
-        // YOUR CODE HERE
-        return null; // Remove this line when implemented
+        int newNumerator = this.numerator * other.denominator - other.numerator * this.denominator;
+        int newDenominator = this.denominator * other.denominator;
+        return new Rational(newNumerator, newDenominator);
     }
 
     // TODO: Static method - r1 - r2
     public static Rational subtract(Rational r1, Rational r2) {
-        // YOUR CODE HERE
-        return null; // Remove this line when implemented
+        return r1.subtract(r2);
     }
 
     // TODO: Instance method - this * other
     // Formula: (a/b) * (c/d) = (a*c) / (b*d)
     public Rational multiply(Rational other) {
-        // YOUR CODE HERE
-        return null; // Remove this line when implemented
+        int newNumerator = this.numerator * other.numerator;
+        int newDenominator = this.denominator * other.denominator;
+        return new Rational(newNumerator, newDenominator);
     }
 
     // TODO: Static method - r1 * r2
     public static Rational multiply(Rational r1, Rational r2) {
-        // YOUR CODE HERE
-        return null; // Remove this line when implemented
+        return r1.multiply(r2);
     }
 
     // TODO: Instance method - this / other
@@ -83,13 +83,17 @@ public class Rational {
         // YOUR CODE HERE
         // HINT: Division is multiplication by reciprocal
         // Don't forget to check if other.numerator is zero!
-        return null; // Remove this line when implemented
+        if (other.numerator == 0) {
+            throw new ArithmeticException("Cannot divide by zero.");
+        }
+        Rational otherReciprocal = new Rational(other.denominator, other.numerator);
+        return this.multiply(otherReciprocal);
+
     }
 
     // TODO: Static method - r1 / r2
     public static Rational divide(Rational r1, Rational r2) {
-        // YOUR CODE HERE
-        return null; // Remove this line when implemented
+        return r1.divide(r2);
     }
 
     //  PROVIDED - String representation