CSCI A201/A597 and I210 Homework Four Solutions Second semester 2000-2001

Date: Tue, 20 Feb 2001 02:50:57 -0500 (EST)
From: Adrian German <dgerman@cs.indiana.edu>
To: Andrey Salaev <asalaev@cs.indiana.edu>,
     Adrian German <dgerman@cs.indiana.edu>,
     Francisco Lara-Dammer <flaradam@cs.indiana.edu>, malani@indiana.edu,
     myadroff@indiana.edu, Alex Leykin <oleykin@cs.indiana.edu>,
     Robert Najlis <rnajlis@cs.indiana.edu>, sapark@indiana.edu,
     sgrogg@indiana.edu, vpavlor@indiana.edu, Ying Jin <yinjin@cs.indiana.edu>,
     Zhen Pan <zhpan@cs.indiana.edu>
Subject: Assignment Four posted


/* Solution for assignment 4, posted just now, due March 3rd 11:59pm.

   Notice grading is particularly objective this time: they need to
   define 5 instance methods, 4 predicates, one constructor. Give up
   to 9.5 for each, for a total of up to 95, which is an A. Allow the
   extra 5 points for surprisingly exceptional work that deserves an
   A+ without hesitation.

   Let me know if I can be of any help.

... Adrian */

class Fraction {

    private int numerator;
    private int denominator;

    public Fraction(int num, int den) {
	int divisor;
	if (den == 0) {
	    System.out.println(" Fraction with denominator zero!");
	    System.exit(1);
	}
        if (num == 0) { numerator = 0; denominator = 1; }
        else {
	    if (den < 0) {
		num *= -1;
		den *= -1;
	    }
	    if ((divisor = Euclid.gcd(num, den)) != 1) {
		num /= divisor;
		den /= divisor;
	    }
	    numerator = num;
	    denominator = den;
	}
    }

    public String toString() {
	String fraction;
	if (denominator == 1) { fraction = numerator + ""; }
        else { fraction = numerator + "/" + denominator; }
	if (denominator * numerator < 0) {
	    return "(" + fraction + ")";
	} else {
	    return fraction;
	}

    }

    public boolean isZero() {
	return (denominator == 1 && numerator == 0);
    }

    public boolean isInt() {
	return (denominator == 1);
    }

    public boolean equals(Fraction other) {
	return (numerator == other.numerator && denominator == other.denominator);
    }

    public boolean greaterThan(Fraction other) {
	return (numerator * other.denominator >
                denominator * other.numerator);
    }

    public Fraction minus(Fraction other) {
	return new Fraction(
                     numerator * other.denominator - other.numerator * denominator,
		     denominator * other.denominator
		   );
    }

    public Fraction plus(Fraction other) {
	return new Fraction(
	             numerator * other.denominator + other.numerator * denominator,
                     denominator * other.denominator
                   );
    }

    public Fraction times(Fraction other) {
	return new Fraction(numerator * other.numerator, denominator * other.denominator);
    }

    public Fraction divideBy(Fraction other) {
	return new Fraction(numerator * other.denominator, denominator * other.numerator);
    }

    public static void main(String[] args) {
	Fraction f = new Fraction(6, 9);
	Fraction g = new Fraction(-4, 6);
	System.out.println("Test of operations: ");
	System.out.println("  Add: " + f + " + " + g + " = " + f.plus(g));
	System.out.println("  Sub: " + f + " - " + g + " = " + f.minus(g));
	System.out.println("  Mul: " + f + " * " + g + " = " + f.times(g));
	System.out.println("  Div: " + f + " / " + g + " = " + f.divideBy(g));
	System.out.println("Test of predicates: ");
	System.out.print("  1. Does " + f + " equal " + g + "? ");
	System.out.println(" The answer is: " + f.equals(g));
	Fraction h = new Fraction(8, -2);
	System.out.print("  2. Is " + h + " an integer? ");
	System.out.println("The answer is: " + h.isInt());
	Fraction i, j;
	i = (f.minus(g)).times(f.plus(g));
	j = f.times(f).minus(g.times(g));
	System.out.print("  3. Does " + i + " equal " + j + "? ");
	System.out.println("The answer is: " + i.equals(j));
	System.out.print("  4. Is 5/8 greater than 2/3? The answer is: ");
	System.out.println((new Fraction(5, 8)).greaterThan(new Fraction (2, 3)));

    }
}

class Euclid {
    static int gcd(int a, int b) {
	a = Math.abs(a);
        b = Math.abs(b);
	if (a == 0) return b; // 0 is error value
	if (b == 0) return a;
        int temp;
        while (b > 0) {
            temp = a % b;
	    a = b;
	    b = temp;
	}
	return a;
    }
}

boolean equals(Fraction other) {
  return (this.minus(other)).isZero(); 
} 

boolean isPositive() {
  return numerator * denominator > 0; 
} 

boolean greaterThan(Fraction other) {
  return (this.minus(other)).isPositive(); 
}