Manipulating Objects

• Encapsulating is a key principle of Object Oriented Programming.

  • Internal Data is private
  • Access to Data is regulated through public methods
  • Accessor and Mutator Methods

  

• Can ensure data integrity by regulating access.

  • Update as a whole , rather than individual components.

    

• Question: Does this provide sufficient control??

Querying a Database

• Object stores train reservation information
  • Can query availability for a given train and date.
• To control spamming by bots → require user to log in before querying.
• So → Need to connect the query to the logged in status of the user.

<aside> 💡 Interaction with State

</aside>

• How to do this → Use objects!

  • On log in , user receives an object that can make a query.
  • Object is created from private class that can lookup railwaydb.

  

• How does user know of the capabilities of private class QueryObject ?

  • Use an interface!

  • Interface describes the capability of the object returned in login.

    

• Query Object allows unlimited number of queries.

  • Limit the number of queries per login
    • Maintain a Counter

      • Add instance variables to object returned on login

      • Query object can remember the state of the interaction.