The Adding Calculator ver 0.02

package theaddingcalculator;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;

public class Addingcalculator {
    private int number1;
    private int number2;
    private char operation;

    Addingcalculator(int number1, char operation, int number2) {
        this.number1 = number1;
        this.number2 = number2;
        this.operation = operation;
    }

    Addingcalculator() {
        Scanner scan = new Scanner(System.in);
        System.out.println("Write operation: ");
        String separatedInput = addingCalculatorInputFormat(scan.nextLine());
        this.number1 = Integer.valueOf(separatedInput.substring(0, separatedInput.indexOf(' ')));
        this.operation = separatedInput.charAt(separatedInput.indexOf(' ') + 1);
        this.number2 = Integer.valueOf(separatedInput.substring(separatedInput.lastIndexOf(' ') + 1));
    }

    private String addingCalculatorInputFormat(String scanLine) {
        String separatedLine = "";
        boolean sign = false;
        List<Character> operationSign = new ArrayList<>(Arrays.asList('+', '-', '/', '*', '^'));
        separatedLine += scanLine.charAt(0);
        for (int i = 1; i < scanLine.length(); i++) {
            if (!sign && operationSign.contains(scanLine.charAt(i))) {
                separatedLine += " " + scanLine.charAt(i) + " ";
                sign = true;
            } else if (!sign && scanLine.charAt(i) != ' ') {
                separatedLine += scanLine.charAt(i);
            } else if (sign && scanLine.charAt(i) != ' ') {
                separatedLine += scanLine.charAt(i);
            }

        }
        return separatedLine;
    }

    // private int Math.negateExact(int number) {
    // int Math.negateExactNumber = Integer.MIN_VALUE;
    // while (number + Math.negateExactNumber != 0) {
    // Math.negateExactNumber++;
    // }
    // return Math.negateExactNumber;
    // }

    private int adding(int number1, int number2) {
        return number1 + number2;
    }

    private int subtraction(int number1, int number2) {
        return number1 + Math.negateExact(number2);
    }

    private int multiply(int number1, int number2) {
        int result = 0;
        int signNumber1 = 0;
        int signNumber2 = 0;
        if (number2 < 0) {
            signNumber2 = Math.negateExact(number2);
        } else {
            signNumber2 = number2;
        }
        if (number1 < 0) {
            signNumber1 = Math.negateExact(number1);
        } else {
            signNumber1 = number1;
        }
        for (int i = 0; i < signNumber2; i++) {
            result += signNumber1;

        }
        if (multiplySign(number1, number2))
            return result;
        else
            return Math.negateExact(result);

    }

    private boolean multiplySign(int number1, int number2) {
        return ((number1 > 0 && number2 > 0) || (number1 < 0 && number2 < 0));

    }

    private boolean dividePreCalulateIsInteger(int number1, int number2) {
        if ((number1 > 0 && number1 < number2) || (number1 < 0 && Math.negateExact(number1) < number2)) {
            System.out.println("Non-integral answer");
            return false;
        } else if (number1 == 0 && number2 == 0) {
            System.out.println("Not-defined");
            return false;
        } else if (number2 == 0) {
            System.out.println("Divide by 0 error!");
            return false;

        } else {
            if ((number1 > 0 && divideIsInteger(number1, number2) == number1)
                    || (number1 < 0 && divideIsInteger(number1, number2) == Math.negateExact(number1)))
                return true;
            else
                System.out.println("Non-integral answer");
            return false;
        }

    }

    private int divideIsInteger(int number1, int number2) {

        return divideHidden(number1, number2, true);
    }

    private int divideAnswer(int number1, int number2) {
        return divideHidden(number1, number2, false);
    }

    private int divideHidden(int number1, int number2, boolean whichInt) {
        int isInteger = 0;
        int answer = 0;
        int signNumber1 = 0;
        int signNumber2 = 0;
        if (number2 < 0) {
            signNumber2 = Math.negateExact(number2);
        } else {
            signNumber2 = number2;
        }
        if (number1 < 0) {
            signNumber1 = Math.negateExact(number1);
        } else {
            signNumber1 = number1;
        }
        while (isInteger < signNumber1) {
            isInteger += signNumber2;
            answer++;
        }
        if (!multiplySign(number1, number2))
            answer = Math.negateExact(answer);
        if (whichInt) {
            return isInteger;
        }
        return answer;
    }

    private boolean exponentationIsInteger(int number1, int number2) {
        if (number2 < 0) {
            System.out.println("Non-integral answer");
            return false;
        }
        return true;

    }

    private int exponentation(int number1, int number2) {
        int result;
        int signNumber1 = 0;
        if (number2 == 0) {
            result = 1;
        } else {
            if (number1 < 0) {
                signNumber1 = Math.negateExact(number1);
            } else {
                signNumber1 = number1;
            }
            result = signNumber1;
            int multiplier = 0;
            for (int i = 1; i < number2; i++) {
                for (int j = 0; j < signNumber1; j++) {
                    multiplier += result;
                }
                result = multiplier;
                multiplier = 0;
            }
        }
        if (evenExponentChecker(number1, number2) || number1 > 0)
            return result;
        else
            return Math.negateExact(result);
    }

    public boolean evenExponentChecker(int number1, int number2) {
        int helper = 0;
        for (int i = 0; i <= number2; i += 2)

            helper = number2 + Math.negateExact(i);

         return helper == 0;

    }

    public void signCollector(int number1, char operation, int number2) {
        int result = 0;
        boolean error = false;
        switch (operation) {
        case '+':
            result = adding(number1, number2);
            break;
        case '-':
            result = subtraction(number1, number2);
            break;
        case '*':
            result = multiply(number1, number2);
            break;
        case '/':
            if (dividePreCalulateIsInteger(number1, number2))
                result = divideAnswer(number1, number2);
            else
                error = true;
            break;
        case '^':
            if (exponentationIsInteger(number1, number2))
                result = exponentation(number1, number2);
            else
                error = true;
            break;
        default:
            System.out.println("Sign of operation is not recognized");
            break;

        }
        if (!error)
            System.out.println(number1 + " " + operation + " " + number2 + " = " + result);
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Addingcalculator calc = new Addingcalculator();
        calc.signCollector(calc.number1, calc.operation, calc.number2);
    }

}