Question

Lets say I have a class like this in Java:

public class Function {
    public static int foo(int n) {
        return n+1;
    }
}

What happens if I call the foo method like this from a thread?

x = Function.foo(y);

Can I do that with two threads, without them waiting for each other? Let’s say that foo takes a while, and that it gets called a lot, so that each thread would would likely be trying to use foo at the same time. Can they do that, or do I have to make all the methods in Function instance methods and give each thread it’s own Function object?

Answer 1

The code you are calling does not store any state, and thus will return deterministically whether called from one thread or many – and its not like the “lines of code” needs to be guarded (as you seem to imply by your question), because its ok to run the “same lines of code” from multiple threads, provided they dont share data (which in this case, doesnt).

Problem comes if you had code like

public class Function {
    private static int last = 0;
    public static int foo(int n) {
        last += n; 
        return last; 
    }
}

this is when you start to need to worry about different threads clobbering the static last.