Final answer:
The Lamp class can have a boolean variable to store whether it is lit or not. Encapsulation in object-oriented programming involves hiding internal details and providing access through methods. Getters and setters methods can be used to maintain encapsulation. Preventing direct access to instance variables helps maintain data integrity, control access to sensitive data, and improve code maintainability.
Step-by-step explanation:
a) The instance variable for the Lamp class can be a boolean variable named 'lit' which stores whether the lamp is lit or not. The methods for the Lamp class can include a constructor to initialize the 'lit' variable, a method to check whether the lamp is lit or not, and a method to change the state of the lamp.
b) Encapsulation in object-oriented programming refers to the practice of hiding the internal details of an object and providing access to them through methods. It helps in maintaining data integrity, improving code reusability, and allowing for easier updates or modifications.
c) An example of how encapsulation is maintained is through the use of getters and setters methods. These methods provide controlled access to the instance variables of a class. For the Lamp class, a getter method can be used to check whether the lamp is lit or not, and a setter method can be used to change the state of the lamp.
d) The advantages of preventing direct access to instance variables include maintaining data integrity, controlling access to sensitive data, and improving code maintainability. By preventing direct access to instance variables, the class can ensure that any changes to the variables are done through controlled methods, reducing the risk of unintentional modifications or data inconsistencies.