Is IntelliJ's java singleton thread-safe

Question

IntelliJ can autogenerate a template for a singleton class, which looks something like this:

public class A {
    private static A ourInstance = new A();

    public static A getInstance() {
        return ourInstance;
    }

    private A() {
    }
}

Is this implementation of singleton thread-safe? I have read about implementing thread-safe singletons through enums. I was wondering if the above implementation is thread-safe as well. As 'ourInstance' has been defined as static and initialized as a class variable, there should be just one copy of the object.

Answer 1

Yes, this implementation is thread-safe. Static fields are guaranteed to be initialised and visible before this class or any instance of it are available to the rest of java code.

Answer 2

您需要将final添加到static变量ourInstance以防止以后进行任何修改，然后您将拥有一个完美的线程安全singleton 。