Limit the number of DIRECT Instances of a class
class Parent
{
    .............
    .........
    ..............
}

class Child1 extends Parent
{
    .............
    .........
    ..............
}

class Child2 extends Parent
{
    .............
    .........
    ..............
}

static final AtomicInteger count = new AtomicInteger();

// in your Parent constructor.
if (getClass() == Parent.class && count.incrementAndGet() >= LIMIT)
   throw new IllegalStateException();

public class Parent  {

    public Parent() {
        if (count.incrementAndGet() >= LIMIT) { //count is an AtomicInt/Long
            throw new InstantiationException("Too many instances");
        }

    protected Parent(boolean placeholder) { //protected means only subclasses can call it
        //do nothing with the placeholder, but it differentiates the two constructors
    }

}