Calculator.java

package simplejavacalculator;

import static java.lang.Double.NaN;

import static java.lang.Math.log;

import static java.lang.Math.log10;

import static java.lang.Math.pow;

public class Calculator {

    public enum BiOperatorModes {

        normal, add, minus, multiply, divide , xpowerofy 

    }

    public enum MonoOperatorModes {

        square, squareRoot, oneDividedBy, cos, sin, tan ,log , rate, abs

    }

    private Double num1, num2;

    private BiOperatorModes mode = BiOperatorModes.normal;

    private Double calculateBiImpl() {

        if (mode == BiOperatorModes.normal) {

            return num2;

        }

        if (mode == BiOperatorModes.add) {

            if (num2 != 0) {

                return num1 + num2;

            }

            return num1;

        }

        if (mode == BiOperatorModes.minus) {

            return num1 – num2;

        }

        if (mode == BiOperatorModes.multiply) {

            return num1 * num2;

        }

        if (mode == BiOperatorModes.divide) {

            return num1 / num2;

        }

        if (mode == BiOperatorModes.xpowerofy) {

            return pow(num1,num2);

        }

        // never reach

        throw new Error();

    }

    public Double calculateBi(BiOperatorModes newMode, Double num) {

        if (mode == BiOperatorModes.normal) {

            num2 = 0.0;

            num1 = num;

            mode = newMode;

            return NaN;

        } else {

            num2 = num;

            num1 = calculateBiImpl();

            mode = newMode;

            return num1;

        }

    }

    public Double calculateEqual(Double num) {

        return calculateBi(BiOperatorModes.normal, num);

    }

    public Double reset() {

        num2 = 0.0;

        num1 = 0.0;

        mode = BiOperatorModes.normal;

        return NaN;

    }

    public Double calculateMono(MonoOperatorModes newMode, Double num) {

        if (newMode == MonoOperatorModes.square) {

            return num * num;

        }

        if (newMode == MonoOperatorModes.squareRoot) {

            return Math.sqrt(num);

        }

        if (newMode == MonoOperatorModes.oneDividedBy) {

            return 1 / num;

        }

        if (newMode == MonoOperatorModes.cos) {

            return Math.cos(Math.toRadians(num));

        }

        if (newMode == MonoOperatorModes.sin) {

            return Math.sin(Math.toRadians(num));

        }

        if (newMode == MonoOperatorModes.tan) {

            if (num == 0 || num % 180 == 0) {

                return 0.0;

            }

            if (num % 90 == 0 && num % 180 != 0) {

                return NaN;

            }

            return Math.tan(Math.toRadians(num));

        }

        if (newMode == MonoOperatorModes.log) {

            return log10(num);

        }

        if (newMode == MonoOperatorModes.rate) {

           return num / 100;

        }