Calculator Helper

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class CalcHelper {

    private void appStart() {
        System.out.println("Press any key to continue...");
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

        try {
            reader.readLine();
        }

        catch (IOException e) {
            e.getStackTrace();
        }
    }

    public void printInstructions() {
        System.out.println("Welcome to Simple Java Calculator.");

        try {
            Thread.sleep(1000);
        }
        // Exception handling
        catch (InterruptedException e) {
            e.getStackTrace();
        }

        appStart();

        System.out.println("Enter two numbers and the desired mathematical operation.");
    }

    // Reading doubles
    public double readDouble() {
        double input = 0;
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

        // Read the input
        try{
        input = Double.parseDouble(reader.readLine());
        }

        // Handle exceptions
        catch (IOException e) {
            e.getStackTrace();
        }

        catch(NumberFormatException e) {
            System.out.println("Oops, something went wrong. Try again, please.");
            readDouble();   // Restart if things go wrong
        }
        return input;
    }

    // Reading strings
    public String readString() {
        String s = ""; // default operator is plus
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

        try {
            s = reader.readLine();
        }

        // Handle exception
        catch (IOException e) {
            e.getStackTrace();
        }

        return s;
    }


    // Selecting operation
    public void operationSelect(String operator, double a, double b) {
        switch(operator) {

            // Summation
            case "+":
            {
                double result = a + b;
                System.out.println(a + " + " + b + " equals " + result);
                break;
            }

            // Subtraction
            case "-":
            {
                double result = a - b;
                System.out.println(a + " - " + b + " equals " + result);
                break;
            }

            // Division
            case "/":

            case ":": {
                double result = 0;

                try {
                    result = a / b;
                }

                catch (ArithmeticException e) {
                    e.getStackTrace();
                }

                System.out.println(a + " / " + b + " equals " + result);
                break;
            }


            // Multiplication
            case "*": {
                double result = a * b;
                System.out.println(a + " * " + b + " equals " + result);
                break;

            }

            // In case of the error
            default:
                System.out.println("Unknown operation");
                break;
        }
    }
}