Java Reflection example

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Scanner;


public class Main {

    public static void main(String[] args) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException, NoSuchFieldException {

        Class blackBoxClass = BlackBoxInt.class;  // We get a hold of the class with  all private fields and methods
        Constructor intConstructor = blackBoxClass.getDeclaredConstructor(int.class);  // There are 2 constructors - without parameters(sets the "innerValue" field to 0 - by default) and one with only one integer
        intConstructor.setAccessible(true);  // We make it accessible, because it is private
        BlackBoxInt blackBoxInt = (BlackBoxInt) intConstructor.newInstance(0);  // We make a new instance of "BlackBoxInt" using ".newInstance()" (The better way)

        Scanner sc = new Scanner(System.in);  // Simple "Scanner"
        String line = sc.nextLine();

        while(!line.equals("END")){  // We will recieve the commands in this format: "<commands>_<value>", that's why we split by "_"
            String[] tokens = line.split("_");

            Method method = blackBoxClass.getDeclaredMethod(tokens[0], int.class);  // Get the method
            doSomething(Integer.valueOf(tokens[1]), method, blackBoxInt);

            System.out.println(getInnerValue(blackBoxInt));  // Get the "innerValue" field which is private

            line = sc.nextLine();
        }

    }

    static void doSomething(int value, Method method, BlackBoxInt blackBoxInt) throws InvocationTargetException, IllegalAccessException {
        method.setAccessible(true);  // Make it accessible, because it's private
        method.invoke(blackBoxInt, value);  // Invoke it(we need a reference, that's why the first parameter is a "BlackBoxInt" instance
    }

    static int getInnerValue(BlackBoxInt blackBoxInt) throws IllegalAccessException, NoSuchFieldException {  // Here we just return the "innerValue" field, so the user can see it
        Field innerValue = blackBoxInt.getClass().getDeclaredField("innerValue");
        innerValue.setAccessible(true);
        return (int) innerValue.get(blackBoxInt);
    }
}

// This down here is the "BlackBoxInt" class



public class BlackBoxInt {

    private static final int DEFFAULT_VALUE = 0;

    private int innerValue;

    private BlackBoxInt(int innerValue) {
        this.innerValue = innerValue;
    }

    private BlackBoxInt() {
        this.innerValue = DEFFAULT_VALUE;
    }

    private void add(int addend) {
        this.innerValue += addend;
    }

    private void subtract(int subtrahend) {
        this.innerValue -= subtrahend;
    }

    private void multiply(int multiplier) {
        this.innerValue *= multiplier;
    }

    private void divide(int divider) {
        this.innerValue /= divider;
    }

    private void leftShift(int shifter) {
        this.innerValue <<= shifter;
    }

    private void rightShift(int shifter) {
        this.innerValue >>= shifter;
    }
}