## Thursday, 22 December 2016

### Chapter 13 Exercise 14, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

13.14 (Demonstrate the benefits of encapsulation)
Rewrite the Rational class in Listing 13.13 using a new internal
representation for the numerator and denomina- tor. Create an array
of two integers as follows:
private long[] r = new long[2];
Use r[0] to represent the numerator and r[1] to represent the denominator.
The signatures of the methods in the Rational class are not changed, so a client
application that uses the previous Rational class can continue to use this new Rational
class without being recompiled.

// Rational.java: Define a rational number and its associated
// operations such as add, subtract, multiply, and divide
public class Rational extends Number implements Comparable<Rational> {
// Data fields for numerator and denominator
private long[] r = new long[2];
private static int NUMERATOR = 0;
private static int DENOMINATOR = 1;

/** Default constructor */
public Rational() {
this(0, 1);
}

/** Construct a rational with specified numerator and denominator */
public Rational(long numerator, long denominator) {
long gcd = gcd(numerator, denominator);
r[NUMERATOR] = ((denominator > 0) ? 1 : -1) * numerator / gcd;
r[DENOMINATOR] = Math.abs(denominator) / gcd;
}

/** Find GCD of two numbers */
private long gcd(long n, long d) {
long t1 = Math.abs(n);
long t2 = Math.abs(d);
long remainder = t1 % t2;

while (remainder != 0) {
t1 = t2;
t2 = remainder;
remainder = t1%t2;
}

return t2;
}

/** Return numerator */
public long getNumerator() {
return r[NUMERATOR];
}

/** Return denominator */
public long getDenominator() {
return r[DENOMINATOR];
}

/** Add a rational number to this rational */
long n = r[NUMERATOR] * secondRational.getDenominator() +
r[DENOMINATOR] * secondRational.getNumerator();
long d = r[DENOMINATOR] * secondRational.getDenominator();
return new Rational(n, d);
}

/** Subtract a rational number from this rational */
public Rational subtract(Rational secondRational) {
long n = r[NUMERATOR] * secondRational.getDenominator()
- r[DENOMINATOR] * secondRational.getNumerator();
long d = r[DENOMINATOR] * secondRational.getDenominator();
return new Rational(n, d);
}

/** Multiply a rational number to this rational */
public Rational multiply(Rational secondRational) {
long n = r[NUMERATOR] * secondRational.getNumerator();
long d = r[DENOMINATOR] * secondRational.getDenominator();
return new Rational(n, d);
}

/** Divide a rational number from this rational */
public Rational divide(Rational secondRational) {
long n = r[NUMERATOR] * secondRational.getDenominator();
long d = r[DENOMINATOR] * secondRational.r[NUMERATOR];
return new Rational(n, d);
}

@Override
public String toString() {
if (r[DENOMINATOR] == 1)
return r[NUMERATOR] + "";
else
return r[NUMERATOR] + "/" + r[DENOMINATOR];
}

/** Override the equals method in the Object class */
public boolean equals(Object parm1) {
return (this.subtract((Rational) (parm1))).getNumerator() == 0;
}

/** Override the hashCode method in the Object class */
public int hashCode() {
return new Double(this.doubleValue()).hashCode();
}

/** Override the abstract intValue method in java.lang.Number */
public int intValue() {
return (int)doubleValue();
}

/** Override the abstract floatValue method in java.lang.Number */
public float floatValue() {
return (float)doubleValue();
}

/** Override the doubleValue method in java.lang.Number */
public double doubleValue() {
return r[NUMERATOR] * 1.0 / r[DENOMINATOR];
}

/** Override the abstract longValue method in java.lang.Number */
public long longValue() {
return (long)doubleValue();
}

@Override
public int compareTo(Rational o) {
if ((this.subtract(o)).getNumerator() > 0)
return 1;
else if ((this.subtract(o)).getNumerator() < 0)
return -1;
else
return 0;
}
}


public class Exercise_14 {

public static void main(String[] args) {

Rational rational = new Rational(4, 10);
rational = rational.multiply(new Rational(2, 4));
System.out.println(rational);
}
}