I have an unknown error in my Java calculator code

Question

I am a very young and inexperienced Java programmer trying to understand some of the concepts discussed in my high school computer science class.

Currently, I am trying to make a calculator using Java, but have come across an error in my code...I have been trying to figure out the cause of the problem but I am absolutely stuck. I am trying to create a calculator that has users enter an equation on one line, and through parsing, the program should be able to give me a correct answer. Currently I have only programmed the math to calculate equations with two operands (+,-,*,/,^), but I also want my program to calculate equations with single operands (absolute value, sin, cos, tan).

Here is what I have so far:

package calculator;
import java.util.Scanner;

public class Calculator {

public class Maths {

    double add(double a, double b) {
        double answer = a+b;
        return answer;          
    }

    double subtract(double a, double b) {
        double answer = a-b;
        return answer;          
    }

    double multiply(double a, double b) {
        double answer = a*b;
        return answer;          
    }

    double divide(double a, double b) {
        double answer = a/b;
        return answer;          
    }

    double power(double a, double b){
        double answer =a;

        for (int x=2; x<=b; x++){
            answer *= a;
        }

        return answer;
    }

}

public static void main(String[] args) {

    Scanner input = new Scanner(System.in);

    Maths maths = Maths();

    double answer = 0;
    double inputA, inputB;
    char operator;
    boolean done = false;

     while (done == false) {
        System.out.print("Please enter your equation: ");

        inputA = input.nextDouble();
        operator = input.next().charAt(0);
        inputB = input.nextDouble();        

        if (operator == '+') {
            answer = maths.add(inputA, inputB);
        }

        if (operator == '-') {
            answer = maths.subtract(inputA, inputB);
        }

        if (operator == '*') {
            answer = maths.multiply(inputA, inputB);
        }

        if (operator == '/') {
            answer = maths.divide(inputA, inputB);
        }

        if (operator == '^') {
            answer = maths.power(inputA, inputB);
        }

            System.out.println(answer);             
    }       

    input.close();

  }

}

As of right now, I feel as though my code is headed in the right direction: except there is a significant error, the cause of which I am unsure. public class Maths is not working in my main block of code. When I was creating this, I had the idea that I would use procedural decomposition and make a separate method where the computation would take place, while the actual collection of variables would happen in the main class.

My IDE is giving me an error at Maths maths = Maths(); located in the main class.

I would really appreciate it if I could get some help on figuring out and understanding the root of the problem at hand so I can fix my program and can avoid such mistakes in the future!

Thank's in advance

Answer 1

use this code it will work

package calculator;
import java.util.Scanner;

class Maths {

    double add(double a, double b) {
        double answer = a+b;
        return answer;          
    }

    double subtract(double a, double b) {
        double answer = a-b;
        return answer;          
    }

    double multiply(double a, double b) {
        double answer = a*b;
        return answer;          
    }

    double divide(double a, double b) {
        double answer = a/b;
        return answer;          
    }

    double power(double a, double b){
        double answer =a;

        for (int x=2; x<=b; x++){
            answer *= a;
        }

        return answer;
    }

}

public class Calculator {

public static void main(String[] args) {

    Scanner input = new Scanner(System.in);

    Maths maths = new Maths();

    double answer = 0;
    double inputA, inputB;
    char operator;
    boolean done = false;

     while (done == false) {
        System.out.print("Please enter your equation: ");

        inputA = input.nextDouble();
        operator = input.next().charAt(0);
        inputB = input.nextDouble();        

        if (operator == '+') {
            answer = maths.add(inputA, inputB);
        }

        if (operator == '-') {
            answer = maths.subtract(inputA, inputB);
        }

        if (operator == '*') {
            answer = maths.multiply(inputA, inputB);
        }

        if (operator == '/') {
            answer = maths.divide(inputA, inputB);
        }

        if (operator == '^') {
            answer = maths.power(inputA, inputB);
        }

            System.out.println(answer);             
    }       

    input.close();

  }

}

Answer 2

You missed the new here

Maths maths = Maths();

It should be

Maths maths = new Maths();

This Maths is an inner class. So you needs to change the instantiation as follows to corrected all errors.

Maths maths =new Calculator().new Maths();