How to Count Number of Instances of a Class

Question

Can anyone tell me how to count the number of instances of a class?

Here\'s my code

public class Bicycle {

    //instance variables
    public int          


        

Answer 1

Since static variables initialized only once, and they're shared between all instances, you can:

class MyClass {

    private static int counter;

    public MyClass() {
        //...
        counter++;
    }

    public static int getNumOfInstances() {
        return counter;
    }
}

Read more about static fields in the JLS - 8.3.1.1. static Fields:

If a field is declared static, there exists exactly one incarnation of the field, no matter how many instances (possibly zero) of the class may eventually be created. A static field, sometimes called a class variable, is incarnated when the class is initialized (§12.4).

^{Note that counter is implicitly set to zero}