Problem-1: Can you explain about access specifiers in java? Answer: In java , classes,variables,methods and constructor can have access specifiers.There are 4 types of access specifiers.
private
protected
public
default or No specifier or none
There is a point to be noted about constructors in java are treated differently than methods because constructor are not considered a class member.
Class Members are made of two things:
Class's variable
Class' methods
Problem-2 : Given a database application,Can you think of classes to generate unique sequence numbers?
Answer: Here we can use Singleton Pattern to create a counter to provide unique sequential numbers.This is can be used as primary keys in database.
public class SequenceNumber
{
private static SequenceNumber instance;
private static int count;
private SequenceNumber(){
count=0;
}
public static synchronized SequenceNumber getInstance()
{
if(instance==null)
{
instance =new SequenceNumber();
}
return instance;
}
public synchronized int getNext()
{
return ++count;
}
}