Possible issue with inheritance? Value of variables not being passed properly

[J. Deeson]

I have been working on this program for quite a while, and can't figure out what's going on. In TestFraction, I use a while loop and Scanner to get two integers, a and b, from the user, and these values should be turned into the fraction a/b. This is done twice to create two fractions, fr1 and fr2. Then the class Fraction (which I created previously for another project) will perform operations on these two fractions. The issue I'm running into is that rather than getting the values of a and b from Scanner, as in my methods getFraction1 and getFraction2, the values of a and b seem to be set by their initial definition in Fraction, which is a=1, b=1. I know that these values are coming from Fraction because I've attempted to set a and b to other values when they are initialized in TestFraction. Can anyone give me some hints as to what's going on here? I'm quite new to Java, and have a feeling that I'm not understanding something about inheritance.

Here is the output I get:

Input 1st fraction numerator and denominator
1
4
Input 2nd fraction numerator and denominator
3
4
1/1 + 1/1 = 2/1
1/1 - 1/1 = 0/1
1/1 * 1/1 = 1/1
1/1 / 1/1 = 1/1
1/1 1/1 1/1

Here is TestFraction:

package Fraction;

import java.io.*;
import java.util.*;

public class TestFraction 
{   
	
	static Scanner console = new Scanner (System.in); 
	
	private static int getNumber() throws InputMismatchException
	{
			return console.nextInt();
	}
	
	private static Fraction getFraction1() 
	{
		int a=1, b=1;
		Fraction frac = new Fraction ();
		
		while (true) {
			
			// prompt to enter a numerator and a denominator
			System.out.println("Input 1st fraction numerator and denominator");
			// input the numerator and the denominator using getNumber()
			try {
				a = getNumber();
				b = getNumber();
				}
			catch (Exception e)
			{
				System.out.println("Exception: "+e.toString());
				console.nextLine();
				continue;
			}
			return frac;
			// return new Fraction if OK
			// otherwise print an error message
		}
	}
	
	private static Fraction getFraction2() 
	{
		int a=1, b=1;
		Fraction frac = new Fraction ();
		
		while (true) {
			
			// prompt to enter a numerator and a denominator
			System.out.println("Input 2nd fraction numerator and denominator");
			// input the numerator and the denominator using getNumber()
			try {
				a = getNumber();
				b = getNumber();
			}
			
			catch (Exception e)
			{
				System.out.println("Exception: "+e.toString());
				console.nextLine();
				continue;
			}
			return frac;
			// return new Fraction if OK
			// otherwise print an error message
		}
	}
	public static void main(String[] args)
	{   
		Fraction fr1 = new Fraction ();
		fr1 = getFraction1();
		
		Fraction fr2 = new Fraction ();
		fr2 = getFraction2();
		
		Fraction res = new Fraction();
	
		// define other variables including res and fr2
		
		res  = Fraction.add  (fr1, fr2);
		System.out.println(fr1+" + "+fr2+" = "+res);  
		
		res	 =	Fraction.subtract (fr1, fr2);
		System.out.println(fr1+" - "+fr2+" = "+res);
		res          =     Fraction.multiply (fr1, fr2);
		System.out.println(fr1+" * "+fr2+" = "+res);
		res          =     Fraction.divide (fr1, fr2);
		System.out.println(fr1+" / "+fr2+" = "+res);
		res          =     Fraction.lessThan (fr1, fr2);
		System.out.println(fr1+" "+res+" "+fr2);
		
		// test subtract, multiply, divide, lessThan methods
		//    each test has to print a description, a result, 
		//    and, possibly, a error message if the calculation fails
	
	}

}

And Fraction:

package Fraction;

public class Fraction 
{
	protected int a;
	protected int b;
	public Fraction()
	{
		a = 1;
		b = 1;
	}
	public Fraction (int a, int b)
	{
		this.a=a;
		this.b=b;
	}
	public int getNumerator()
	{
		return a;
	}
	public int getDenominator()
	{
		return b;
	}
	public void setNumerator(int a)
	{
		this.a=a;
	}
	
	public void setDenominator(int b)
	{
		this.b=b;
	}
	public String toString ()
	{
		return a+"/"+b;
	}
	public int gcd(int a, int b)
	{
		//ToDo   implement Euclide algorithm
		if (b==0) return a;
   		return gcd(b, a%b);
    }
	public void lowestTerms()
	{   
		int g=gcd(a,b);
		a=a/g;
		b=b/g;
	}
	public static Fraction add(Fraction first, Fraction second)
	{
		Fraction result = new Fraction();
		result.setNumerator(first.getNumerator()*second.getDenominator()
				          + first.getDenominator()*second.getNumerator());
	    result.setDenominator(first.getDenominator()*second.getDenominator());
	    result.lowestTerms();
		return result;
	}
	//ToDo methods subtract, multiply, divide, lessThan 
	public static Fraction subtract(Fraction first, Fraction second)
	{
		Fraction result = new Fraction();
		result.setNumerator(first.getNumerator()*second.getDenominator() 
						  - first.getDenominator()*second.getNumerator());
		result.setDenominator(first.getDenominator()*second.getDenominator());
		result.lowestTerms();
		return result;
	}
	public static Fraction multiply(Fraction first, Fraction second)
	{
		Fraction result = new Fraction();
		result.setNumerator(first.getNumerator()*second.getNumerator());
		result.setDenominator(first.getDenominator()*second.getDenominator());
		result.lowestTerms();
		return result;
	}
	public static Fraction divide(Fraction first, Fraction second)
	{
		Fraction result = new Fraction();
		result.setNumerator(first.getNumerator()*second.getDenominator());
		result.setDenominator(first.getDenominator()*second.getNumerator());
		result.lowestTerms();
		return result;
	}
	public static Fraction lessThan(Fraction first, Fraction second)
	{
		if (first.getNumerator()*second.getDenominator() <= 
				first.getDenominator()*second.getNumerator()){
		return first;
		}
		else {
		return second;
		} 
	}
}

[Henry Wong]

J. Deeson wrote:Can anyone give me some hints as to what's going on here?

	private static Fraction getFraction1() 
	{
		int a=1, b=1;
		Fraction frac = new Fraction ();
		
		while (true) {
			
			// prompt to enter a numerator and a denominator
			System.out.println("Input 1st fraction numerator and denominator");
			// input the numerator and the denominator using getNumber()
			try {
				a = getNumber();
				b = getNumber();
				}
			catch (Exception e)
			{
				System.out.println("Exception: "+e.toString());
				console.nextLine();
				continue;
			}
			return frac;
			// return new Fraction if OK
			// otherwise print an error message
		}
	}
	

Nothing to do with inheritance. When do you actually set the values into the fraction?

Henry

[J. Deeson]

Well, I thought that I was setting the values with getFraction1 and getFraction2, but that's apparently not happening.

[Paul Clapham]

J. Deeson wrote:Well, I thought that I was setting the values with getFraction1 and getFraction2, but that's apparently not happening.

Not in the version of the code you posted, you didn't. Those methods both create a Fraction object, but they don't do anything with it. Could you point out the code which you think is setting the values, then? There must be a misconception which needs to be cleared up.

[Henry Wong]

J. Deeson wrote:Well, I thought that I was setting the values with getFraction1 and getFraction2, but that's apparently not happening.

Not sure from your response if you are agreeing with me -- and realized that the values are not being set in the getFraction1() and getFraction2() methods. Or is still confused and believe that it is being set.

Henry

[J. Deeson]

Here is where I believe I am setting it. What I meant was, I have written getNumber in such a way that I think I am using Scanner to get the integers that are typed by the user, and storing these two integers as a and b. Here is where I think I am setting the value of fr1 and fr2 (I realize that I'm not actually doing so, as it's not working):
getFraction1 uses getNumber to capture the user's input:

System.out.println("Input 1st fraction numerator and denominator");
			// input the numerator and the denominator using getNumber()
			try {
				a = getNumber();
				b = getNumber();
				}

Then, getNumber uses Scanner to get these two integers:

private static int getNumber() throws InputMismatchException
	{
			return console.nextInt();
	}
	

Where is this going wrong?

[Henry Wong]

J. Deeson wrote:Here is where I believe I am setting it. What I meant was, I have written getNumber in such a way that I think I am using Scanner to get the integers that are typed by the user, and storing these two integers as a and b. Here is where I think I am setting the value of fr1 and fr2 (I realize that I'm not actually doing so, as it's not working):
getFraction1 uses getNumber to capture the user's input:

System.out.println("Input 1st fraction numerator and denominator");
			// input the numerator and the denominator using getNumber()
			try {
				a = getNumber();
				b = getNumber();
				}

Then, getNumber uses Scanner to get these two integers:

private static int getNumber() throws InputMismatchException
	{
			return console.nextInt();
	}
	

Where is this going wrong?

Another hint... when you do this?

a = getNumber();

Which "a" variable are you setting? ... and BTW, it is *not* the variable that you think it is !!

Henry

[J. Deeson]

I actually figured it out. I was able to simply use the setters in Fraction by adding the lines:

//return fr2;
			frac.setNumerator(a);
			frac.setDenominator(b);
			return frac;

to set the values of a and b in getFraction1 and getFraction2.

Thanks for your help!