Object Oriented Programming (Java)

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Why it matters

Java powers Android (3 billion devices), enterprise systems (banks, e-commerce), and big data (Hadoop, Spark). OOP principles apply to every modern language — learn Java, understand software design.

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Placement relevance

70% of service companies (TCS, Infosys, Wipro, Cognizant) primarily hire Java developers. Most backend roles use Spring/Spring Boot. Android development = Java/Kotlin. FAANG uses Java for system design.

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Prerequisites for

Spring Framework · Android Development · Enterprise Applications · Design Patterns · Microservices · Software Engineering

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Recommended books

Head First Java by Kathy Sierra and Bert Bates · Effective Java by Joshua Bloch · Core Java Volume I by Cay S. Horstmann · Thinking in Java by Bruce Eckel

Create a Java program demonstrating multilevel inheritance with 3 classes: Vehicle → Car → SportsCar. Include method overriding and constructor chaining.

Write a Java program to implement a custom exception 'InvalidAgeException'. Throw this exception if age < 18. Handle it using try-catch block.

Implement a multithreaded program where two threads print even and odd numbers alternately from 1 to 20 using synchronization.

Explain the difference between abstract class and interface in Java. Write a program demonstrating both with real-world example.

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Write complete programs

Don't write pseudocode or snippets. Include: package, imports, class definition, main method, proper syntax. Incomplete programs lose 30-40% marks even if logic is correct.

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Comment your code

Add 2-3 line comments explaining logic, especially for inheritance/polymorphism. Shows understanding. Examiners appreciate clarity.

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Master the 4 pillars

Encapsulation, Inheritance, Polymorphism, Abstraction — these 4 concepts are ALWAYS asked. Practice explaining with code + real-world analogies (Car-Vehicle, Animal-Dog).

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Thread questions are tricky

Synchronization is confusing. Practice: producer-consumer, even-odd printing, race conditions. Understand synchronized keyword, wait(), notify(). Draw diagrams showing thread states.