Java reflection update number

I am new to Java reflection. I am trying to make a program where addition of two numbers gives custom result. Below is the code:

public class MoreTest {

    public static void main(String[] args) {

        try {
            Field field = Integer.class.getDeclaredField( "value" );
            field.setAccessible( true );
            field.setInt(Integer.valueOf(2),2);             

        } catch (NoSuchFieldException | SecurityException | IllegalArgumentException | IllegalAccessException e) {
            e.printStackTrace();
        }

        Integer a = 2;
        Integer b = 4;

        System.out.println( a + b ); // should print 8
    }

}

What I can do in the above code to print the output I need?