Assigning static final int in a JUnit (4.8.1) test suite

Question

I have a JUnit test class in which I have several static final ints that can be redefined at the top of the tester code to allow some variation in the test values. I have logic in my @BeforeClass method to ensure that the developer has entered values that won't break my tests.

I would like to improve variation further by allowing these ints to be set to (sensible) random values in the @BeforeClass method if the developer sets a boolean useRandomValues = true;. I could simply remove the final keyword to allow the random values to overwrite the initialisation values, but I have final there to ensure that these values are not inadvertently changed, as some tests rely on the consistency of these values.

1. Can I use a constructor in a JUnit test class? Eclipse starts putting red underlines everywhere if I try to make my @BeforeClass into a constructor for the test class, and making a separate constructor doesn't seem to allow assignment to these variables (even if I leave them unassigned at their declaration);

2. Is there another way to ensure that any attempt to change these variables after the @BeforeClass method will result in a compile-time error?

3. Can I make something final after it has been initialised?

Answer 1

You can do this with a static constructor:

import java.util.Random;
public class StaticRandom
{
  private static final boolean useRandomValues = true;
  private static final Random r = new Random();
  private static final int value1;
  private static final int value2;
  private static final int value3;
  static
  {
    if(useRandomValues)
    {
      value1 = r.nextInt();
      value2 = r.nextInt();
      value3 = r.nextInt();
    }
    else
    {
      value1 = 0;
      value2 = 0;
      value3 = 0;
    }
  }
}

Answer 2

You can use a static initializer:

final static boolean useRandomValues = true;

final static int valueA;
final static int valueB;
static {
    if(!useRandomValues) {
        valueA = 42;
        valueB = 1337;
    }
    else {
        Random rnd = new Random();
        valueA = rnd.nextInt(100);
        valueB = rnd.nextInt(100);
    }
}