Favour Underscores for Numbers

When dealing with numbers going above 6 digits, it can be difficult to quickly understand the exact figure they represent. By favouring underscores in our Java variables they become far more readable as can be seen from the examples below.
public final class TestNumberDefinitions {

    public static int NORMAL_MILLION = 1000000;
    public static int FORMATTED_MILLION = 1_000_000;
    
    public static long NORMAL_BILLION = 1000000000;
    public static long FORMATTED_BILLION = 1_000_000_000;
    
    public static long NORMAL_TRILLION = 1000000000000;
    public static long FORMATTED_TRILLION = 1_000_000_000_000;
}
This can also be utilised for standardised formats such as credit card numbers in your test cases.
public static long CREDIT_CARD_NUMBER = 0000_1234_1234_1234_1234;
public static int SORT_CODE = 12_34_56;
formatting
readability
data