Question

Let’s say we just have a simple object Person with int ID which identifies it. How can I give new ID value (+1) for each new instance of Person but in constructor of that class Person? (I use no DB for this)

Answer 1

Use a static AtomicInteger:

final class Foo {
  private static final AtomicInteger seed = new AtomicInteger();
  private final int id;

  public Foo() {
    this.id = seed.incrementAndGet();
  }
}

See here for more information: https://stackoverflow.com/a/4818753/17713