Simple Design Pattern Interview Questions

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.

1. private
2. protected
3. public
4. 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;

}

}