Objects (OOP) (OCR A Level Computer Science)
Revision Note
Written by: Craig Godbold
Reviewed by: James Woodhouse
Objects (OOP)
What is an Object?
An object is a representation of a real-world entity eg teacher, aeroplane, mobile phone, cat etc
A class is like a blueprint that describes the properties and behaviours of objects, while an object is a specific instance created based on that blueprint with its own unique values for the properties
A constructor is a special method within a class that is automatically called when an object of that class is created (instantiated)
Constructors typically define the initial values of instance variables and perform any necessary setup to prepare the object for use
Example of 2 objects belonging to a class
Worked Example
A supermarket uses an object-oriented approach to organise items that it offers for sale. Part of the class definition for the ItemForSale class is shown below:
class ItemForSale public itemName public price public discount
Write a line of code to create an object of type ItemForSale called mushypeas that has a name of “mushy peas” and a price of £0.89
[3]
How to answer this question:
Creating object with identifier
mushypeas =
creating object as type
ItemForSale
mark for parameters passed in as needed ("mushy peas",0.89) [1 mark]
Answer:
Example answer 1 to get full marks:
mushypeas=new ItemForSale("mushy peas", 0.89)
Example answer 2 to get full marks:
ItemForSale mushypeas = ItemForSale(“mushy peas”,0.89);
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