分数相等程序中的输出不正确

Question

I'm a beginner java programmer writing a program to test the equality of two user-inputted fractions. There's a Fraction class that includes: mutator methods for setting the numerators and denominators, a method for displaying the fraction as a ratio, and a method for testing equality. There's also a Main class that allows the user to create fractions. I'm having trouble getting the correct output. It appears no matter the input, the fractions are always "NOT equal". Here is an example:

This application allows you to test if two fractions are equal to each other.
Enter the numerator of the first fraction: 1
Enter the denominator of the first fraction: 2
The fraction you entered is: 1/2
Enter the numerator of the target fraction: 2
Enter the denominator of the target fraction: 4
The target fraction you entered is: 2/4
The two fractions being compared are 1/2 and 2/4...
The two fractions are NOT equal.
Would you like to test another fraction? Enter 0 to quit anything else to continue.

Here is the code for the class Fraction:

public class Fraction {

    int numerator1;
    int denominator1;
    int numerator2;
    int denominator2;

    public void Fraction() {
        numerator1 = 0; //initialize variables
        denominator1 = 1;
        numerator2 = 0;
        denominator2 = 1;
    }

    public void setNum1(int num) { //mutator method
        numerator1 = num;
    }

    public void setDen1(int denom) { //mutator method
        denominator1 = denom;
    }

    public void setNum2(int num) {
        numerator2 = num;
    }

    public void setDen2(int denom) {
        denominator2 = denom;
    }

    public boolean equals(int numerator1, int numerator2, int denominator1, int denominator2) {
        double frac1;
        double frac2;
        frac1 = numerator1/denominator1;
        frac2 = numerator2/denominator2;

        if(frac1 == frac2)
            return true;
        else
            return false;
    }

    public String displayFraction1() {
        String ratio1;
        ratio1 = (numerator1 + "/" + denominator1);
        return ratio1;
    }

    public String displayFraction2() {
        String ratio2;
        ratio2 = (numerator2 + "/" + denominator2);
        return ratio2;
    }
}

Here is the code for the class Main :

import java.util.*;

public class Main {

    public static void main(String[] args) {

        Fraction create = new Fraction(); //creating fraction objects
        Fraction target = new Fraction();
        int num1, num2; //stores numerators of 2 fractions
        int den1, den2; //stores denominators of 2 fractions
        int input = 1; //initialized to 1 for while loop
        Scanner keyboard = new Scanner(System.in); 

        System.out.println("This application allows you to test if two fractions are equal to each other.");
        System.out.print("Enter the numerator of the first fraction: ");
        num1 = keyboard.nextInt();
        create.setNum1(num1);
        System.out.print("Enter the denominator of the first fraction: ");
        den1 = keyboard.nextInt();
        create.setDen1(den1);
        System.out.println("The fraction you entered is: " + create.displayFraction1());

        while(input != 0) { //allows user to hold initial fraction and repeatedly tests against with target fractions
            System.out.print("Enter the numerator of the target fraction: ");
            num2 = keyboard.nextInt();
            target.setNum2(num2);
            System.out.print("Enter the denominator of the target fraction: ");
            den2 = keyboard.nextInt();
            target.setDen2(den2);
            System.out.println("The target fraction you entered is: " + target.displayFraction2());
            System.out.println("The two fractions being compared are " + create.displayFraction1() + " and " + target.displayFraction2() + "...");      

            if(create.equals(target)) //calls equals method to test equality
                System.out.println("The two fractions are equal.");
            else
                System.out.println("The two fractions are NOT equal.");

            System.out.println("Would you like to test another fraction? Enter 0 to quit anything else to continue.");
            input = keyboard.nextInt();
            }
    }
}

Answer 1

The equals() method presented in your code for class Fraction is not the same one being invoked by Main.main() . You provide Fraction.equals(int, int, int, int) , which would make more sense as a static method, but main() invokes the equals(Object) method that Fraction inherits from Object .

If you want to override Object 's method, then your method must have the same parameter type(s).

Update: Note also that the code for your equals(int, int, int, int) method is also erroneous, as @nhouser9 observed in his now-deleted answer. You are performing integer divisions to try to compute floating-point quotients for comparison, and this will give you many false positives.

Really, it's questionable to use floating-point at all, because most fractions are not exactly representable as double s. It would be better to test for equality by cross-multiplying:

return (long) numerator1 * denominator2 == (long) numerator2 * denominator1;

If you do that then do not neglect the casts to long , for otherwise some possible inputs will cause overflow.

Alternatively, you could reduce both fractions to their simplest terms, and compare that way. Presumably you would use Euclid's method to compute the GCDs needed for the reductions.