help with interfaces

**r035198x** · Jan 25 '07, 05:57 AM

Originally posted by xxbabysue123xx

THe question is:

Modify the RationalNumber Class so that it implements the Comparable interface. To perform the comparison, compute an equivalent floating point value from the numerator and denominator for both Rational objects, then compare them using a tolerence value of 0.0001. Write a main driver to test your modifications.

I tried by got an error (see last program)

// THE Original Program
// Rational.java Author: Lewis/Loftus

public class Rational
{
private int numerator, denominator;

public Rational (int numer, int denom)
{
if (denom == 0)
denom = 1;

// Make the numerator "store" the sign
if (denom < 0)
{
numer = numer * -1;
denom = denom * -1;
}

numerator = numer;
denominator = denom;

reduce();
}

public int getNumerator ()
{
return numerator;
}

public int getDenominator ()
{
return denominator;
}

public Rational reciprocal ()
{
return new Rational (denominator, numerator);
}

public Rational add (Rational op2)
{
int commonDenominat or = denominator * op2.getDenomina tor();
int numerator1 = numerator * op2.getDenomina tor();
int numerator2 = op2.getNumerato r() * denominator;
int sum = numerator1 + numerator2;

return new Rational (sum, commonDenominat or);
}

public Rational subtract (Rational op2)
{
int commonDenominat or = denominator * op2.getDenomina tor();
int numerator1 = numerator * op2.getDenomina tor();
int numerator2 = op2.getNumerato r() * denominator;
int difference = numerator1 - numerator2;

return new Rational (difference, commonDenominat or);
}

public Rational multiply (Rational op2)
{
int numer = numerator * op2.getNumerato r();
int denom = denominator * op2.getDenomina tor();

return new Rational (numer, denom);
}

public Rational divide (Rational op2)
{
return multiply (op2.reciprocal ());
}

public boolean equals (Rational op2)
{
return ( numerator == op2.getNumerato r() &&
denominator == op2.getDenomina tor() );
}

public String toString ()
{
String result;

if (numerator == 0)
result = "0";
else
if (denominator == 1)
result = numerator + "";
else
result = numerator + "/" + denominator;

return result;
}

private void reduce ()
{
if (numerator != 0)
{
int common = gcd (Math.abs(numer ator), denominator);

numerator = numerator / common;
denominator = denominator / common;
}
}

private int gcd (int num1, int num2)
{
while (num1 != num2)
if (num1 > num2)
num1 = num1 - num2;
else
num2 = num2 - num1;

return num1;
}
}

//MY PROGRAM

public class Rational implements Comparable

{
private int numerator, denominator;

public Rational (int numer, int denom)
{
if (denom == 0)
denom = 1;

if (denom < 0)
{
numer = numer * -1;
denom = denom * -1;
}

numerator = numer;
denominator = denom;

reduce();
}

public int getNumerator ()
{
return numerator;
}

public int getDenominator ()
{
return denominator;
}

public Rational reciprocal ()
{
return new Rational (denominator, numerator);
}

public Rational add (Rational op2)
{
int commonDenominat or = denominator * op2.getDenomina tor();
int numerator1 = numerator * op2.getDenomina tor();
int numerator2 = op2.getNumerato r() * denominator;
int sum = numerator1 + numerator2;

return new Rational (sum, commonDenominat or);
}

public Rational subtract (Rational op2)
{
int commonDenominat or = denominator * op2.getDenomina tor();
int numerator1 = numerator * op2.getDenomina tor();
int numerator2 = op2.getNumerato r() * denominator;
int difference = numerator1 - numerator2;

return new Rational (difference, commonDenominat or);
}

public Rational multiply (Rational op2)
{
int numer = numerator * op2.getNumerato r();
int denom = denominator * op2.getDenomina tor();

return new Rational (numer, denom);
}

public Rational divide (Rational op2)
{
return multiply (op2.reciprocal ());
}

public boolean equals (Rational op2)
{
return ( numerator == op2.getNumerato r() &&
denominator == op2.getDenomina tor() );
}

public String toString ()
{
String result;

if (numerator == 0)
result = "0";
else
if (denominator == 1)
result = numerator + "";
else
result = numerator + "/" + denominator;

return result;
}

private void reduce ()
{
if (numerator != 0)
{
int common = gcd (Math.abs(numer ator), denominator);

numerator = numerator / common;
denominator = denominator / common;
}
}

private int gcd (int num1, int num2)
{
while (num1 != num2)
if (num1 > num2)
num1 = num1 - num2;
else
num2 = num2 - num1;
return num1;
}
public float compute ()
{
float value = getNumerator() / getDenominator( );
return value;
}
public int compareTo(Ratio nal op2)
{
if (Math.abs(compu te() - op2.compute()) < .0001)
return 0;
if (compute() > op2.compute())
return + 1;
if (compute() < op2.compute())
return - 1;
}
}
THIS IS WHAT I HAVE AND I GET THE ERROR :Rational.java: 7: Rational should be declared abstract; it does not define compareTo(java. lang.Object) in Rational. THANKS FOR THE HELP

Please use code tags next time when posting code.

When a class implements an interface, it signs a contract. The contract says that I shall have all the methods in the interface I am implementing otherwise I shall be declared abstract.
Now your Rational class implements Comparable meaning it must contain a method called with the signature

Code:

int compareTo (Object o)

**xxbabysue123xx** · Jan 25 '07, 03:26 PM

would this work..and how would i put tolerance in the compareTo method

public double getDecimalEquiv alent()
{
return (double)numerat or/denominator;
}

public int compareTo(Objec t obj)
{
double TOLERANCE=0.000 1;
Rational myRational = (Rational) obj;
double result = getDecimalEquiv alent() -
myRational.getD ecimalEquivalen t();
if (result > 0)
return 1;
else if (result < 0)
return -1;
return 0;
}

**xxbabysue123xx** · Jan 25 '07, 03:44 PM

or would this work..

public double getDecimalEquiv alent()
{
return (double)numerat or/denominator;
}

public int compareTo(Objec t obj)
{
double tolerance=0.000 1;
Rational myRational = (Rational) obj;
double result = getDecimalEquiv alent() -
myRational.getD ecimalEquivalen t();
if (result < tolerance)
return 0;
else if (getDecimalEqui valent() >myRational.get DecimalEquivale nt())
return +1;
else
return -1;
}

**r035198x** · Jan 25 '07, 03:45 PM

Originally posted by xxbabysue123xx

would this work..and how would i put tolerance in the compareTo method

public double getDecimalEquiv alent()
{
return (double)numerat or/denominator;
}

public int compareTo(Objec t obj)
{
double TOLERANCE=0.000 1;
Rational myRational = (Rational) obj;
double result = getDecimalEquiv alent() -
myRational.getD ecimalEquivalen t();
if (result > 0)
return 1;
else if (result < 0)
return -1;
return 0;
}

You should use {} to make your if else statements more readable.
You forgot the tolerence value of 0.0001.

**r035198x** · Jan 25 '07, 03:51 PM

Originally posted by xxbabysue123xx

or would this work..

public double getDecimalEquiv alent()
{
return (double)numerat or/denominator;
}

public int compareTo(Objec t obj)
{
double tolerance=0.000 1;
Rational myRational = (Rational) obj;
double result = getDecimalEquiv alent() -
myRational.getD ecimalEquivalen t();
if (result < tolerance)
return 0;
else if (getDecimalEqui valent() >myRational.get DecimalEquivale nt())
return +1;
else
return -1;
}

Try

Code:

public int compareTo(Object obj) {
		double tolerance=0.0001;
		Rational myRational = (Rational) obj;
		double result = getDecimalEquivalent() - myRational.getDecimalEquivalent();
		if(Math.abs(result) > 0.0001) {
			//not equal
			if(getDecimalEquivalent() > myRational.getDecimalEquivalent()) {
				//bigger
				return 1;
			}
			else {
				//smaller
				return -1;
			}
		}
		else {
			//equal
			return 0;
		}
	}

And tell me how it goes

P.S You are still forgetting to wrap your code with code tags

**xxbabysue123xx** · Jan 25 '07, 10:33 PM

it works now...thank you very much for your help

**r035198x** · Jan 26 '07, 05:32 AM

Originally posted by xxbabysue123xx

it works now...thank you very much for your help

Good. Come back for help anytime. And don't forget to help others as well where you can.

**dubdos** · Oct 16 '07, 10:20 PM

I was just assigned this program too, but when I use the code provided placed into the code seen in the sample here:

private int gcd (int num1, int num2)
{
while (num1 != num2)
if (num1 > num2)
num1 = num1 - num2;
else
num2 = num2 - num1;

return num1;
}

public int compareTo(Objec t obj)
{
double tolerance=0.000 1;
RationalNumber myRational = (RationalNumber ) obj;
double result = getDecimalEquiv alent() -
myRational.getD ecimalEquivalen t();

if(Math.abs(res ult) > 0.0001)
{

if(getDecimalEq uivalent() > myRational.getD ecimalEquivalen t())
{
return 1;
}

it does not compile. The error message says: cannot find symbol - method getDecimalEquiv alent().

If anyone is still out there, please help!

**JosAH** · Oct 17 '07, 05:55 AM

Originally posted by dubdos

it does not compile. The error message says: cannot find symbol - method getDecimalEquiv alent().

If anyone is still out there, please help!

Well, you forgot to copy/paste the getDecimalEquiv alent() method or if you typed
it over you made a typo somewhere.

kind regards,

Jos

help with interfaces

help with interfaces

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