Java method question

[Mahlon Berv]

I'm having trouble understanding a certain Java problem.

Below is the class for the problem

 public class Fraction {
 
  public static int numberOfFractions=0;  
  private int num;
  private int den;
  
  Fraction(int n, int d) {                   // 1st constructor
    numberOfFractions++;
    num = n;
    den = d;
  }
  
  Fraction() {                              // second constructor
    numberOfFractions++;
    num = 0;
    den = 1;
  }
  
  public void setFraction(int n, int d) {
    if (d != 0)  {
        num = n;
        den = d;
    }
  }
  
  public int getNumerator() {
    return num;
  }
  
  public int getDenominator() {
    return den;
  }
  
  public void print() {
    System.out.println (num+"/"+den);
  }
  
  public void invert() {
    int temp;
    if (num!=0)  {
        temp = num;
        num = den;
        den = temp;
    }
  }
  
 
 

 public double toDouble() {
    // Code
  }
 
  public void multByFraction(Fraction x) {
    num = num * x.getNumerator();
    den = den * x.getDenominator();
  }
  
  public void addToFraction(Fraction x) {
    if (den != x.getDenomenator()) {
        num = (num * x.getDenomenator())+(x.getNumerator()*den);
        den = den * x.getDenominator();
    }
    else num = num+x.getNumerator();
  }
  
}
 
 
 

Question

1. What will be printed out when the following code is run?

Fraction a = new Fraction(2,3);
Fraction b = new Fraction();
b.invert();
b.addToFraction(new Fraction(3,4));
a.addToFraction(b);
a.print();

(1) 7/6
(2) 17/12
(3) 5/7
(4) 6/7
(5) 2/1

we are also supposed to trace the program. I get stuck on b.addToFraction(new Fraction(3,4));, what is happening there? If somebody could explain the whole program for me that would be great.

Thanks

[Jimmy Clark]

Do you understand how to write Java code?

[Mahlon Berv]

Well i'm pretty new to java, I'm taking AP computer science, but I know the basic stuff, I just need help distinguishing what that particular method, AddTofraction does, what objects are manipulated and how the variables are affected by it.

[Henry Wong]

I get stuck on b.addToFraction(new Fraction(3,4));, what is happening there? If somebody could explain the whole program for me that would be great.

It would help if you actually take a shot at it. You can't learn if you are unwilling to take a guess on what it is doing... but... to answer your question....

It is calling the addToFraction() method, on the object referenced by the b variable. And it is passing it a Fraction object which is instantiated on the same line.

Henry

[Rob Spoor]

Also keep in mind that b.invert() does not what you may think it does since b.num == 0.