What is a compile time constant expression in Java?

Question

I have read that final variables in Java should be instantiated to compile time constant expression. I couldn't understand what is compile time constant expression.

class A {
    int i;
    int j  = i * 5;
}

Is `i * 5 a compile time constant expression?

Answer 1

A "compile time constant expression" is a value that can be calculated during compilation. For example, int MINUTES_IN_DAY = 24 * 60;

As for your reading that final variables should always be instantiated in that form: that's an incorrect generalisation. There are many instances where you need a final to be evaluable at runtime, such as when setting up Runnable s.

Note that static final variables do not need to be compile-time constants either: you can initialise them using static initialisers .