Struggling with toString method in Java

Question

I have created a Class which can add, subtract, multiply or divide two rational numbers. However I am struggling with the toString method. As I create the result in the main method, how do I finish my toString method as my compiler is telling me "result cannot be resolved to a variable". Thank you

public class Rational { 

 private static int num; 
 private static int denom; 

 public Rational() {
     num = 0;
     denom = 1;
 } 

 public Rational(int num, int denom) {
     this.num = num;
     this.denom = denom;
 } 

 public int getNum() {
     return num;
 } 
 public int getDenom() {
     return denom;
 } 
 public Rational add(Rational rhs) { 
 return new Rational(num*rhs.denom+rhs.num*denom, denom*rhs.denom); 
 } 

 public Rational subtract(Rational rhs) { 
     return new Rational(num*rhs.denom-rhs.num*denom, denom*rhs.denom); 
     } 

 public Rational multiply(Rational rhs) { 
     return new Rational(num*rhs.num, denom*rhs.denom); 
     }  

 public Rational divide(Rational rhs) { 
     return new Rational(num*rhs.denom, denom*rhs.num); 
     }  

 public String toString() {

    String str = "" ;
     return "" ;
 }


    public static void main(String[] args) {
         Rational r1 = new Rational(1, 2); // 1/2 
         Rational r2 = new Rational(3, 4); // 3/4 
         Rational result = new Rational(); 
         result = r1.add(r2); 
         System.out.println( result.toString() ); 
         } 
}

Answer 1

public String toString() {
    return num + "/" + denom;
}