(Convert decimals to fractions) Write a program that prompts the user to enter a decimal number and displays the number in a fraction. Hint: read the decimal number as a string, extract the integer part and fractional part from the string,

/*********************************************************************************
* (Convert decimals to fractions) Write a program that prompts the user to enter *
* a decimal number and displays the number in a fraction. Hint: read the decimal *
* number as a string, extract the integer part and fractional part from the      *
* string, and use the BigInteger implementation of the Rational class in         *
* Programming Exercise 13.15 to obtain a rational number for the decimal number. *
*********************************************************************************/
import java.math.BigInteger;
import java.util.Scanner;

public class Exercise_13_19 {
	/** Main method */
	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);

		// Prompt the user to enter a decimal number
		System.out.print("Enter a decimal number: ");
		String[] decimal = input.nextLine().split("[.]");

		// Create a Rational object of the integer part of the decimal number
		Rational r1 = new Rational(new BigInteger(decimal[0]), BigInteger.ONE);

		// Create a Rational object of the fractional part of the decimal number
		Rational r2 = new Rational(new BigInteger(decimal[1]), new BigInteger(
			String.valueOf((int)Math.pow(10, decimal[1].length()))));

		// Display fraction number
		System.out.println("The fraction number is " + 
			(decimal[0].charAt(0) == '-' ? (r1).subtract(r2) : (r1).add(r2)));
	}
}

Rational.java

import java.math.*;

public class Rational extends Number implements Comparable {
	// Data fields for numerator and denominator
	private BigInteger[] r = new BigInteger[2];

	/** Construct a ratinoal with default properties */
	public Rational() {
		this(BigInteger.ZERO, BigInteger.ONE);
	}

	/** Construct a rational with specifiec numerator and denominator */
	public Rational(BigInteger numerator, BigInteger denominator) {
		BigInteger gcd = gcd(numerator, denominator);
		r[0] = (denominator.compareTo(BigInteger.ZERO) > 0
			? BigInteger.ONE : new BigInteger("-1")).multiply(
			numerator.divide(gcd));
		r[1] = denominator.divide(gcd);
	}

	/** Find GCD of two numbers */
	private static BigInteger gcd(BigInteger n, BigInteger d) {
		BigInteger n1 = n;
		BigInteger n2 = d;
		BigInteger gcd = BigInteger.ONE;

		for (BigInteger k = BigInteger.ONE; 
			k.compareTo(n1) <= 0 && k.compareTo(n2) <= 0; 
			k = k.add(BigInteger.ONE)) {
			if (n1.remainder(k).compareTo(BigInteger.ZERO) == 0 && 
				n2.remainder(k).compareTo(BigInteger.ZERO) == 0)
				gcd = k;
		}

		return gcd;
	}

	/** Return numerator */
	public BigInteger getNumerator() {
		return r[0];
	}

	/** Return denominator */
	public BigInteger getDenominator() {
		return r[1];
	}

	/** Add a rational number to this rational */
	public Rational add(Rational secondRational) {
		BigInteger n = (r[0].multiply(secondRational.getDenominator())).add(
			r[1].multiply(secondRational.getNumerator()));
		BigInteger d = r[1].multiply(secondRational.getDenominator());
		return new Rational(n, d);
	}

	/** Subtract a rational number from this rational */
	public Rational subtract(Rational secondRational) {
		BigInteger n = (r[0].multiply(secondRational.getDenominator())).subtract(
			r[1].multiply(secondRational.getNumerator()));
		BigInteger d = r[1].multiply(secondRational.getDenominator());
		return new Rational(n, d);
	}

	/** Mulitply a rational number by this rational */
	public Rational multiply(Rational secondRational) {
		BigInteger n = r[0].multiply(secondRational.getNumerator());
		BigInteger d = r[1].multiply(secondRational.getDenominator());
		return new Rational(n, d);
	}

	/** Divide a rational number by this rational */
	public Rational divide(Rational secondRational) {
		BigInteger n = r[0].multiply(secondRational.getDenominator());
		BigInteger d = r[1].multiply(secondRational.getNumerator());
		return new Rational(n, d);
	}

	@Override
	public String toString() {
		if (r[1].compareTo(BigInteger.ONE) == 0)
			return r[0] + "";
		else
			return r[0] + "/" + r[1];
	}

	@Override // Override the equals method in the Object class
	public boolean equals(Object other) {
		if (((this.subtract((Rational)(other))).getNumerator()).compareTo(
			BigInteger.ZERO) == 0)
			return true;
		else
			return false;
	}

	@Override // Implement the abstract intValue method in Number
	public int intValue() {
		return (int)doubleValue();
	}

	@Override // Implement the abstract floatValue method in Number
	public float floatValue() {
		return (float)doubleValue();
	}

	@Override // Implement the doubleValue method in Number
	public double doubleValue() {
		return this.getNumerator().doubleValue() / 
			this.getDenominator().doubleValue();
	}

	@Override // Implement the abstract longValue method in Number
	public long longValue() {
		return (long)doubleValue();
	}

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