Introduction to Object Oriented Programming Concepts
ICSE Class 9 · Computer Applications · Chapter 1
What this chapter covers
- Procedure oriented and object oriented programming
- Data abstraction
- Encapsulation
- Inheritance
- Polymorphism
- Open source software and OpenJDK
- IDEs, Java versions and system requirements
- Java compilation process
- Features of Java
- Real-time applications of Java
Key points
- A program is a set of instructions that tells a computer how to perform a task.
- Procedure oriented programming divides a program into functions working on shared data; object oriented programming builds a program from objects that combine data and methods.
- An object has a state (characteristics) and a behaviour (actions).
- The four principles of OOP are data abstraction, encapsulation, inheritance and polymorphism.
- Data abstraction shows the essential features and hides the background details.
- Encapsulation binds data and methods into one unit and protects the data (data hiding).
- Inheritance lets a derived class acquire the features of a base class, which allows reuse of code.
- Polymorphism lets one message or method name take many forms.
- Open source software is free to use, study, change and share; OpenJDK is the open source Java development kit.
- An IDE such as BlueJ, DrJava, NetBeans or MyEclipse brings editing, compiling, running and debugging together.
- Java has been released in versions; LTS versions such as Java 17, 21 and 25 receive updates for several years.
- A Java applet runs inside a web browser; a Java application runs on its own and begins from `main`.
- Source code (`.java`) is compiled by `javac` into byte code (`.class`), which the JVM converts into object code for the processor.
- Java's main features are simple, object oriented, platform independent, robust and secured, along with portability, multithreading and a rich library.
- Java is used in mobile, desktop, web, gaming, robotic and education applications, and in chatbots and virtual assistants.
Questions answered
Define object oriented programming.
Object oriented programming is an approach in which a program is built from objects, each combining data and the functions that work on that data into a single unit, with objects working together by sending messages to one another.
State two differences between procedure oriented programming and object oriented programming.
In procedure oriented programming the basic unit is a procedure and data is mostly shared by all functions; in object oriented programming the basic unit is an object and data is kept protected inside objects. Procedure oriented programming follows a top-down design, while object oriented programming follows a bottom-up design.
Define data abstraction and give one real-life example.
Data abstraction is the act of representing the essential features of an object while hiding the background details. A person drives a car using the steering wheel, accelerator and brakes without knowing how the engine works inside.
What is encapsulation? How does it help to protect data?
Encapsulation is the wrapping up of data and the functions that operate on it into a single unit. Since the data can be reached only through the unit's own functions, no other part of the program can change it directly, which protects it from careless change (data hiding).
Name the principle of OOP that allows code to be reused, and explain it with an example.
Inheritance. A class `Student` can inherit a name and address from a class `Person` and add a roll number of its own, so the common features are written once and reused.
What is polymorphism? Give a real-life example.
Polymorphism is the ability of a single message or method name to take more than one form, behaving differently depending on the object it acts on. The message "make a sound" makes a dog bark and a cat mew.
Why do schools often prefer open source software? Name the open source Java development kit suggested by the syllabus.
Open source software is free to install on every computer, its code can be studied and improved, and errors are fixed quickly by a large community. The suggested kit is OpenJDK (Open Java Development Kit).
What is an IDE? Name any two IDEs used for Java.
An IDE (Integrated Development Environment) is a software application that brings together an editor, compiler, runner and debugger in one window. BlueJ and NetBeans are two IDEs for Java.
Past board exam questions
ICSE 2027 sample paper · 1 mark
Megha knows how to bake cookies in the microwave oven, but she does not know about the internal, unseen components of the microwave oven. Identify the OOPs feature depicted in this scenario.
- Abstraction
- Polymorphism
- Inheritance
- Modularity
Show answer
Abstraction
ICSE 2027 sample paper · 5 marks
Answer the following questions: (a) Name the type of error which occurs while compiling a program. (b) Which Java package is imported by default? (c) Define an object in Java. (d) What is the full form of JDK? (e) What is the Math method to convert – 4 to 4?
Show answer
(a) Syntax error (compile-time error).
(b) java.lang
(c) An object is an instance of a class; it has its own state (data members) and behaviour (methods).
(d) Java Development Kit
(e) Math.abs( ) — Math.abs(-4) returns 4.
ICSE 2027 sample paper · 2 marks
(a) Raj climbs 5 floors by climbing 14 steps to reach each floor. Name the programming concept that can be used to depict the same. (b) Identify the Object-Oriented Programming concept implemented in the scene below: A mother says “Son, I am base class” and her son replies “Mom, I am derived class”.
Show answer
(a) Nested loop (an outer loop for the 5 floors and an inner loop for the 14 steps of each floor).
(b) Inheritance (the derived class inherits from the base class).