Which class implements IdGenerator in a thread-safe manner, so that no threads can get a duplicate id value current access?

Given the interface:

Public interface Idgenerator {

int getNextId();

}

Which class implements IdGenerator in a thread-safe manner, so that no threads can get a duplicate id value current access?

A.
Public class generator Implements IdGenerator {
Private AtomicInteger id = new AtomicInteger (0);
return id.incrementAndget();
}
}

B.
Public class Generator Implements idGenerator {
private int id = 0;
return ++id;
}
}

C.
Public class Generator Implements IdGenerator {
private volatile int Id = 0;
return + + Id;
}

D.
Public class Generator Implements IdGenerator {
private int id = 0;
public int getNextId() {
synchronized (new Generator()) {
return + + id;
}
}
}

E.
Public class Generator Implements IdGenerator {
private int id = 0;
public int getnextId() {
synchronized (id) {
return + + id;
}
}
}

Explanation:
Code that is safe to call by multiple threads simultanously is called thread safe. If a piece of code is thread safe, then it contains no race conditions. Race condition only occur when multiplethreads update shared resources. Therefore it is important to know what resources Java threads share when executing.

In Java you can mark a method or a block of code as synchronized. Synchronized blocks can be used to avoid race conditions.