ABSTRACT CLASSES AND INTERFACES - Introduction to Java Programming: Comprehensive Version - page 522

9 System.out.println(r1 + " + " + r2 + " = " + r1.add(r2));
10 System.out.println(r1 + " - " + r2 + " = " + r1.subtract(r2));
11 System.out.println(r1 + " * " + r2 + " = " + r1.multiply(r2));
12 System.out.println(r1 + " / " + r2 + " = " + r1.divide(r2));
13 System.out.println(r2 + " is " + r2.doubleValue());
14 }
15 }

add

2 + 2/3 = 8/3
2 - 2/3 = 4/3
2 * 2/3 = 4/3
2 / 2/3 = 3
2/3 is 0.6666666666666666

The main method creates two rational numbers, r1 and r2 (lines 5-6), and displays the results
of r1 + r2 , r1 - r2 , r1 x r2 , and r1 / r2 (lines 9-12). To perform r1 + r2 , invoke
r1.add(r2) to return a new Rational object. Similarly, invoke r1.subtract(r2) for r1
- r2 , r1.multiply(r2) for r1 x r2 , and r1.divide(r2) for r1 / r2 .
The doubleValue() method displays the double value of r2 (line 13). The double-
Value() method is defined in java.lang.Number and overridden in Rational .
Note that when a string is concatenated with an object using the plus sign ( + ), the object's
string representation from the toString() method is used to concatenate with the string. So
r1 + " + " + r2 + " = " + r1.add(r2) is equivalent to r1.toString() + " + "
+ r2.toString() + " = " + r1.add(r2).toString() .
The Rational class is implemented in Listing 13.13.

L ISTING 13.13

Rational.java
1 public class Rational extends Number implements Comparable<Rational> {
2 // Data fields for numerator and denominator

3 private long numerator = 0 ;

4 private long denominator = 1 ;

5
6 /** Construct a rational with default properties */

7 public Rational() {

8 this ( 0 , 1 );

9 }
10
11 /** Construct a rational with specified numerator and denominator */

12 public Rational( long numerator, long denominator) {

13 long gcd = gcd(numerator, denominator);

14 this .numerator = ((denominator > 0 ) ? 1 : -1 ) * numerator / gcd;

15 this .denominator = Math.abs(denominator) / gcd;

16 }
17
18 /** Find GCD of two numbers */

19 private static long gcd( long n, long d) {

20 long n1 = Math.abs(n);

21 long n2 = Math.abs(d);

22 int gcd = 1 ;

23
24 for ( int k = 1 ; k <= n1 && k <= n2; k++) {
25 if (n1 % k == 0 && n2 % k == 0 )
26 gcd = k;
27 }
28
29

return gcd;