Java error: The method add(String) is undefined for the type String

Question

Whenever I try to run my code, I get the error "The method add(String) is undefined for the type String," "The method subtract(String) is undefined for the type String," and so on for the multiply and divide methods. I don't know if the rest of my code runs correctly because I haven't been able to run the actual program. Why am I getting this error?

Main:

import java.util.*;

public class RationalNumberMain 
{

      public static void main(String[] args) 
      {

          Scanner s = new Scanner(System.in);

          System.out.print("Enter first fraction here: ");
          String r1 = s.nextLine();

          System.out.print("Enter second fraction here: ");
          String r2 = s.nextLine();

          RationalNumber x = new RationalNumber(r1);
          RationalNumber y = new RationalNumber(r2);

            System.out.println("Rational Number 1 is " + r1);
            System.out.println("Rational number 2 is " + r2);
            System.out.println(r1 + " + " + r2 + " = " + r1.add(r2));
            System.out.println(r1 + " - " + r2 + " = " + r1.subtract(r2));
            System.out.println(r1 + " * " + r2 + " = " + r1.multiply(r2));
            System.out.println(r1 + " / " + r2 + " = " + r1.divide(r2));
      }
}

Class:

public class RationalNumber 
{

    private String fraction;
    private String s1;
    private String s2;
    private int num;
    private int den;
    private int combineNum;
    private int combineDen;
    private String finalFraction;
    private int divideNum;
    private int divideDen;


    public RationalNumber(String userFraction) 
    {
        fraction = userFraction;
        s1 = "";
        s1 = "";
        num = 0;
        den = 0;
        combineNum = 0;
        combineDen = 0;
        finalFraction = "";
        divideNum = 0;
        divideDen = 0;
    }

    public String toString() 
    {
        return fraction;
    }

    public void seperate()
    {
        s1 = fraction.substring(0,1);
        s2 = fraction.substring(2);
        num = Integer.parseInt(s1);
        den = Integer.parseInt(s2);

    }

    public int getNum() 
    {
        return num;
    }

    public int getDen() 
    {
        return den;
    }

    public String add(RationalNumber x) 
    {
        combineDen = den * x.getDen();
        combineNum = (num * x.getDen()) + (x.getNum() * den);
        finalFraction = String.valueOf(combineDen) + "/" + String.valueOf(combineNum);
        return finalFraction;
    }

    public String subtract(RationalNumber x) 
    {
        combineDen = den * x.getDen();
        combineNum = (num * x.getDen()) - (x.getNum() * den);
        finalFraction = String.valueOf(combineDen) + "/" + String.valueOf(combineNum);
        return finalFraction;
    }

    public String multiply(RationalNumber x) 
    {
        combineDen = den * x.getDen();
        combineNum = num * x.getNum();
        finalFraction = String.valueOf(combineDen) + "/" + String.valueOf(combineNum);
        return finalFraction;
    }

    public String divide(RationalNumber x) 
    {
        divideNum = x.getDen();
        divideDen = x.getNum();
        combineDen = den * divideDen;
        combineNum = num * divideNum;
        finalFraction = String.valueOf(combineDen) + "/" + String.valueOf(combineNum);
        return finalFraction;
    }

}

Don't you mean add(x) and add(y) instead of r1 and r2? This is why it's good to use meaningful variable names, not arbitrary ones like x or r. Your method expects a RationalNumber and you are passing a String. — sleepToken
– sleepToken, Commented Feb 6, 2020 at 16:59
Have you a JDK properly installed and configured? Do the code ever ran before? — Hassam Abdelillah
– Hassam Abdelillah, Commented Feb 6, 2020 at 17:00

syntagma · Accepted Answer · 2020-02-06 17:02:18Z

3

r1 is of type String:

String r1 = s.nextLine();

What you want it to add objects of type RationalNumber (created from r1):

RationalNumber x = new RationalNumber(r1);

that is:

x.add(y) instead of r1.add(r2)

And the same for other arithmetic operations in your code.

answered Feb 6, 2020 at 17:02

syntagma

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Comments

fedup · Accepted Answer · 2020-02-06 17:02:31Z

2

These lines of code should be interacting with the rational numbers, not the input.

        System.out.println(r1 + " + " + r2 + " = " + x.add(y));
        System.out.println(r1 + " - " + r2 + " = " + x.subtract(y));
        System.out.println(r1 + " * " + r2 + " = " + x.multiply(y));
        System.out.println(r1 + " / " + r2 + " = " + x.divide(y));

An IDE like IntelliJ would have shown that x and y were created but never used. That would have been a good clue that something was not as you were planning.

answered Feb 6, 2020 at 17:02

fedup

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Comments

Jan Held · Accepted Answer · 2020-02-06 17:06:00Z

0

I am not sure what you expect. java.util.String does not have any of these method add, subtract, multiply, divide.

Did you mean:

System.out.println(r1 + " + " + r2 + " = " + x.add(y));
System.out.println(r1 + " - " + r2 + " = " + x.subtract(y));
System.out.println(r1 + " * " + r2 + " = " + x.multiply(y));
System.out.println(r1 + " / " + r2 + " = " + x.divide(y));

answered Feb 6, 2020 at 17:06

Jan Held

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