How to create a variable that can be set only once but isn't final in Java

Question

I want a class that I can create instances of with one variable unset (the id), then initialise this variable later, and have it immutable after initial

Answer 1

try have an int checker like

private long id = 0;
static int checker = 0;

public void methodThatWillSetValueOfId(stuff){
    checker = checker + 1

    if (checker==1){
        id = 123456;
    } 
}