Question

If I defined Class ‘A’ as a Singleton mean I am able to create only one object of the class ‘A’. If I made it as Serializable and serialized it then How can i achieve the Singleton state of same object?

Answer 1

Quoting Effective Java #77, you should look at implementing readResolve method.

The readResolve feature allows you to substitute another instance for the one
created by readObject [Serialization, 3.7]. If the class of an object being deserial-
ized defines a readResolve method with the proper declaration, this method is
invoked on the newly created object after it is deserialized. The object reference
returned by this method is then returned in place of the newly created object. In
most uses of this feature, no reference to the newly created object is retained, so it
immediately becomes eligible for garbage collection.

public class Elvis implements Serializable {
public static final Elvis INSTANCE = new Elvis();
// readResolve for instance control - you can do better!
private Object readResolve() {
//Return the one true Elvis and let the garbage collector
// take care of the Elvis impersonator.
return INSTANCE;
}
}