Java – volatile variables that will never be assigned null will never contain null?

You can use the following concepts in java examples:

public class X implements Runnable {
    public volatile Object x = new Object();

    @Runnable
    public void run() {
        for (;;) {
            Thread.sleep(1000);
            x = new Object();
        }
    }
}

X read null from another thread?

Bonus: I need to declare that it is fluctuating (I really don't care about this value, as long as it will be a newly allocated value at some time in the future, never null)

Solution

Technically, yes, it is This is the main reason for the original concurrent HashMap's readunderlock Javadoc even explains how to:

Because the value of hashentry is unstable, this type of reordering is legal

The moral of the story is that all non - Final initializations can compete with object constructs

Editor: @ Nathan Hughes asked a valid question:

Doug lea has several comments on this topic. The whole topic can be read here He answered this comment:

There's an answer

And completed: