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

Question

每当我尝试运行我的代码时，都会收到错误“String 类型的方法 add(String) 未定义”、“String 类型的方法 minus(String) 未定义”等等。乘法和除法。我不知道我的其余代码是否正确运行，因为我无法运行实际的程序。为什么我会收到此错误？

主要:

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));
      }
}

类别:

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;
    }

}

Answer 1

r1 的类型为 String:

String r1 = s.nextLine();

您希望它添加 RationalNumber 类型的对象(从 r1 创建):

RationalNumber x = new RationalNumber(r1);

即:

x.add(y) 而不是 r1.add(r2)

代码中的其他算术运算也是如此。