Cannot access private members of same type in Java

Question

I am unable to access private members of same type in Java. I am creating a method 'add' on the Fraction type but I cannot access the other fractions private vars to compare.

public Fraction add(Fraction f) {
    int add1 = (this.numerator*f.denominator)+(this.denominator*f.numerator);
    int add2 = this.denominator*f.denominator;
    return createFraction(add1,add2);
}

Should I be using some sort of reflection feature to achieve this?

Extra info: I have not declared the private members on the interface.

Extra info: I am not permitted to use getters and setters on this class

Extra info: I am not permitted to make those fields public

Answer 1

You should create getters and setters on your Fraction class so you can get the values of the private variables as well as set them.

public class Fraction{
   private int numerator;
   private int denominator;
   public Fraction(final int numerator, final int denominator){
     this.numerator = numerator;
     this.denominator = denominator;
   }
   public int getNumerator(){
     return this.numerator;
   }
   public int getDenominator(){
     return this.denominator;
   }
   public void setNumerator(final int numerator){
    this.numerator = numerator;
   }
   public void setDenominator(final int denominator){
    this.denominator = denominator;
   }
}

You can then change your code to this:

public Fraction add(Fraction f) {
    int add1 = (this.numerator*f.getDenominator())+(this.denominator*f.getNumerator());
    int add2 = this.denominator*f.getDenominator();
    return createFraction(add1,add2); //createFraction can be simply new Fraction(add1, add2);
}

You could use Reflection to get the value of the field by using Field.setAccessible , but it is much easier and cleaner to write a getter for the field.

Example Usage:

Field field = f.getClass().getDeclaredField("numerator"); 
f.setAccessible(true);
int numerator = (int) field.get(f);

Your code could then be changed to:

public Fraction add(Fraction f) throws NoSuchFieldException, IllegalAccessException{
    Field fieldNumerator = f.getClass().getDeclaredField("numerator");
    fieldNumerator.setAccessible(true);
    Field fieldDenominator = f.getClass().getDeclaredField("denominator");
    fieldDenominator.setAccessible(true);
    final int numerator = (int) fieldNumerator.get(f);
    final int denominator = (int) fieldDenominator.get(f);
    int add1 = (this.numerator*denominator)+(this.denominator*numerator);
    int add2 = this.denominator*denominator;
    return createFraction(add1,add2); 
}