Question

I need a class which creates Objects assigning an ID to each Object created. This ID is as usual an int attribute to the class. I want this value (ID) to be increased each time an Object is created and then to be assigned to that Object starting with 1. It strikes me that I need a static int attribute.

How can I initialize this static attribute?

Should I create a separate method to do the increment of the ID (as an ID generator) which is invoked inside the constructor?

What is in general the most effective and well-designed manner to implement that?

Answer 1

Just like you mention use a static int for the id, and increment it when creating new objects.

class MyObject {

    private static int counter = 0;

    public final int objectId;

    MyObject() {
        this.objectId = counter++;
    }
}

Please note that you need to protect counter++ if MyObject is created by multiple threads (for example using AtomicInteger as the other answers suggest).