Lec07 data hiding and encapsulation
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This document discusses data/information hiding and encapsulation. It explains that objects can have private attributes and behaviors that are hidden from outside objects, similar to how people have private spaces and behaviors. It recommends using access modifiers like private to hide attributes and methods from other classes. The document also discusses how encapsulation helps ensure data validity by controlling access to attributes through getters and setters.
Lec07 data hiding and encapsulation
- 1. Data/Information Hiding, Encapsulation Lecture 7 Asif Shahzad, Assistant Professor COMSATS University Islamabad, Lahore Campus
- 2. Private Behavior and Attributes of object • Our home is an object, its kitchen and bedroom are private. We do not allow guests or strangers to visit our kitchen and bedrooms. • In same way, mobile number is our attribute, but we do not share it with everyone. It’s our private attribute. • We do not allow others access or call our certain behavior e.g. shopping and eating. • In same way, an automatic car do not allow the driver to change its gear, it changes it automatically.
- 3. Use Access Modifiers: public or private • We can make certain behavior private, by declaring it with ‘private’ access modifier. Example, hide calculateAverage() • In same way, to make an attribute hidden from outside world, declare it as private e.g. mobileNumber. • Other classes, where object of our class is created, would not be able to read/call private attributes/methods. Private attributes and methods are accessible within the class.
- 5. Encapsulation 1. Lets say, we want Student id be a positive integer. How to do it? Demo.. 2. So, to encapsulate a field, we can make it private and create public get and set methods to give read/write access of attribute to others. 3. In object oriented design, its Student class responsibility to make sure, it will always store a valid id. 4. So encapsulation help to prevent data corruption by other objects / entities.
- 6. Why we declare an attribute as private? • Why we declare an attribute as private? • To ensure data validity • To enforce some organization constraints at write and read opration • To have some private state which other objects has no concern
- 7. Conventions About get/set methods • Method name is prefixed with ‘get’ or ‘set’ followed by attribute name (use camel notation for methods). • The get method's return type must be the type of attribute it returns and it must not receive any argument. • The set method's return type is always void and it must receive only one argument whose type must be same as the type of the attribute being set. • Access modifier for the get and set methods is generally public, but its not a requirement or convention. It can be changed as per application requirements.
- 8. Next ! How we can initialize state at the time of object construction? Constructors