Java Generics and Collections (Meenu Jaiswal Sunil Gupta) (Z-Library)

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Java Generics and Collections A comprehensive guide to type-safe data structures and efficient coding Meenu Jaiswal Sunil Gupta www.bpbonline.com

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First Edition 2026 Copyright © BPB Publications, India eISBN: 978-93-65894-400 All Rights Reserved. No part of this publication may be reproduced, distributed or transmitted in any form or by any means or stored in a database or retrieval system, without the prior written permission of the publisher with the exception to the program listings which may be entered, stored and executed in a computer system, but they can not be reproduced by the means of publication, photocopy, recording, or by any electronic and mechanical means. LIMITS OF LIABILITY AND DISCLAIMER OF WARRANTY The information contained in this book is true and correct to the best of author’s and publisher’s knowledge. The author has made every effort to ensure the accuracy of these publications, but the publisher cannot be held responsible for any loss or damage arising from any information in this book. All trademarks referred to in the book are acknowledged as properties of their respective owners but BPB Publications cannot guarantee the accuracy of this information. www.bpbonline.com

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Dedicated to My beloved parents Late Nand Kishore and Smt Kamlesh Kiran and my husband Pradeep and my kids Suryansh and Purvashi -Meenu Jaiswal My parents, on whose guidance and support I have built my path Late Ramesh Gupta and Smt Kiran Gupta and my wife and son, my greatest source of strength and joy -Sunil Gupta

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About the Authors Meenu Jaiswal is a Java developer with over 13 years of experience in the software industry, contributing to numerous projects across various sectors. Her passion lies in both developing and educating. She is an Oracle Certified Associate Java programmer and holds a full stack engineer certification from IIT Roorkee. She offers advanced Java training sessions focused on practical, real-world applications, and she shares insights on Java, backend programming, and new technologies on LinkedIn. Her expertise spans advanced Java, Spring, Spring Boot, and microservices, which she uses to empower developers in building scalable and efficient solutions. Sunil Gupta is an architect and software developer with over 30 years of experience in application design and development. He specializes in service-oriented architecture (SOA) and design patterns. With 25 years of expertise in Java programming, he has developed innovative solutions across diverse domains, including Fintech, analytics, marketing, robotics, and CAD/CAM. His experience spans both startups and large enterprises, where he combines deep technical knowledge with a strategic approach to create impactful, high-performance products.

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About the Reviewers ❖ Roopa Sunder Raj is a skilled enterprise software engineer and system architect with a strong foundation in designing scalable, cloud-ready, and secure technology solutions, focusing on real-world performance and business impact. Her technical expertise spans system architecture, including microservices, event- driven systems (Kafka), and legacy modernization; cloud and DevOps, with proficiency in AWS, CI/CD pipelines, Kubernetes orchestration, and various deployment strategies; integration and APIs, covering REST, SOAP, service orchestration, and asynchronous messaging; and core technologies such as Java/J2EE, Oracle SQL, and WebLogic. She is also adept in security and compliance, with knowledge of secure coding and OAuth-based authentication/authorization, and in the practical application of AI/ML in enterprise and SMB telecom domains. Her experience further includes OSS/BSS, encompassing end-to-end telecom systems, service lifecycle automation, and TM Forum standards. She has led major transformation initiatives at Charter Communications and Oracle Corporation, including international advisory roles such as optimizing telecom infrastructure for high-volume mobile orders in Australia. Her leadership has encompassed architectural reviews, data backup and storage strategies, and cross-functional solution validation across globally distributed engineering teams. An advocate for diversity in tech, she is also an active member of the National Association for Multi-

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ethnicity in Communications (Platinum Member), Women in Cable Telecommunications, and the Society of Cable Telecommunications Engineers. ❖ Kavita Bora is a highly skilled software engineer with 8.5 years of experience specializing in Java development, Spring Boot, Spring Cloud, Microservices, and web technologies. Demonstrated expertise in delivering innovative solutions for diverse projects, including automation of mail tracking, prevention of product brand delicacy, and open API banking. Strong proficiency in database management using MySQL and PostgreSQL. She is committed to delivering high-quality code and exceeding client expectations.

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Acknowledgements We would like to express our heartfelt gratitude to everyone who has supported us throughout the journey of writing this book. Special thanks to the training programs and organizations where we worked, which enhanced our understanding of the subject matter and helped us strengthen our technical expertise. Our sincere appreciation goes to the team at BPB Publications for their patience, guidance, and flexibility in allowing us the time and creative space to complete this work. Their support in structuring the content and making the publishing process seamless has been invaluable. Meenu Jaiswal: I would like to thank my parents, my late father, whose wisdom and values continue to inspire me, and my mother, whose unwavering encouragement gave me the strength to see this project through. Sunil Gupta: I extend my deepest gratitude to my parents, whose unwavering support, blessings, and guidance have shaped the person I am today. To my beloved family, you are my world. My wife’s boundless love and care, and my son’s remarkable achievements and radiant smiles, inspire me to strive beyond my own expectations. My deepest gratitude goes to my husband and children for their love, patience, and understanding during the many

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hours I spent researching and writing. Without their support, this book would not have been possible.

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Preface This book serves as a comprehensive guide to two fundamental pillars of the Java programming language: Generics and the Collections Framework. Mastering these concepts is essential for developers seeking to produce robust, type-safe, and highly reusable code. The text is structured to provide a logical and progressive learning experience, moving from foundational principles to advanced applications and best practices. This book is crafted with a practical approach, aiming not only to educate on the theoretical aspects of generics and collections but also to empower readers to apply these principles effectively in their own projects. The clear structure and detailed content are intended to guide the learner from a basic understanding to confident, expert- level application. The book is divided into twelve chapters, each dedicated to a specific aspect of generics or collections. The book emphasizes the synergy between these two concepts, illustrating how they work together to create more efficient and powerful applications. By understanding their combined functionality, readers will not only grasp the syntax but also the underlying design philosophy that underpins Java's most robust data structures. Chapter 1: Introduction to Generics- This chapter introduces the core concepts of generics, explaining their role in enhancing type safety and code reusability. You will learn the basic syntax for type parameters and how to

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create your own generic classes and methods. This is the perfect starting point to understand why generics are such a powerful tool in modern Java. Chapter 2: Bounded Types- This section explores how to restrict the types used with your generics. We will cover upper bounds, lower bounds, and wildcards, showing you how to build more flexible and secure code that prevents unexpected errors at compile time. Chapter 3: Generics in Collections- This chapter bridges the gap between generics and the Collections Framework, detailing how to apply generics to everyday data structures like List<String>, Set<Integer>, and Map<String, User>. We will explore how this makes your collection management much safer and easier to read. Chapter 4: Introduction to Collections Framework- This chapter provides a foundational overview of the Collections Framework's architecture. We will look at the main interfaces (Collection, List, Set, Map) and discuss how they all fit together in a logical hierarchy. Chapter 5: List Interface and Implementations- This chapter explores the List interface and its primary implementations, including ArrayList, LinkedList, Vector, and Stack. You will learn the key differences between them. Chapter 6: Map Interface and Implementations- This chapter explores the Map interface and its main implementations, including HashMap, LinkedHashMap, TreeMap, and Hashtable. Chapter 7: Set Interface and Implementations- This section covers the Set interface, which is all about unique elements. You will explore the various implementations, including the fast-but-unordered HashSet, the ordered LinkedHashSet, and the sorted TreeSet, so you know exactly which one to choose for your specific needs.

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Chapter 8: Queue and Deque Interfaces- This section discusses the specialized Queue and Deque interfaces and their implementations, like PriorityQueue and ArrayDeque. Chapter 9: Utility Classes- This chapter covers essential utility classes, such as Collections and Arrays, which provide methods for sorting, searching, and manipulating data. You will discover powerful static methods for sorting, searching, and manipulating your data with ease. Chapter 10: Best Practices with Generics and Collections- This section synthesizes the knowledge by outlining best practices for writing efficient, maintainable, and synchronized code. We will help you avoid common mistakes and write professional-level Java. Chapter 11: Real-world Applications- This chapter demonstrates how generics and collections are used in practical, real-world scenarios through case studies and tangible examples, showing you how to solve common problems. Chapter 12: Future Trends and Next Steps- The book concludes with a summary of key concepts and an exploration of what is next for Java. We will look at recent advancements and future trends, helping you stay ahead.

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Code Bundle and Coloured Images Please follow the link to download the Code Bundle and the Coloured Images of the book: https://rebrand.ly/091a3a The code bundle for the book is also hosted on GitHub at https://github.com/bpbpublications/Java-Generics- and-Collections. In case there’s an update to the code, it will be updated on the existing GitHub repository. We have code bundles from our rich catalogue of books and videos available at https://github.com/bpbpublications. Check them out! Errata We take immense pride in our work at BPB Publications and follow best practices to ensure the accuracy of our content to provide with an indulging reading experience to our subscribers. Our readers are our mirrors, and we use their inputs to reflect and improve upon human errors, if any, that may have occurred during the publishing processes involved. To let us maintain the quality and help us reach out to any readers who might be having difficulties due to any unforeseen errors, please write to us at : errata@bpbonline.com Your support, suggestions and feedbacks are highly appreciated by the BPB Publications’ Family.

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Table of Contents 1. Introduction to Generics Introduction Structure Objectives Generics Background Benefits of generics Basic syntax of generics Defining parameterized types Syntax overview Generic classes Generic methods Bounded type parameters Wildcard types Defining generic classes Using generic methods Generics with constructors No explicit type parameter on the constructor Conclusion Exercise Answers 2. Bounded Types

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Introduction Structure Objectives Upper bounds Lower bounds Key differences between upper and lower bounds Wildcards Best practice Bounded type parameters Examples of bounded types in practice Conclusion Exercise Answers 3. Generics in Collections Introduction Structure Objectives Overview of Java Collections Framework Applying generics to List<T> Wildcards in generic lists Applying generics to Set<T> Wildcards in generic sets Applying generics to Map<K,V> Wildcards in generic maps Common pitfalls and best practices Type erasure in generics Impact of type erasure

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Conclusion Exercise Answers 4. Introduction to Collections Framework Introduction Structure Objectives Overview of Java Collections Framework Collections hierarchy Collection interface Key methods in the collection interface Key methods in collections Iterable interface and iterators Iterator interface Understanding the enhanced for loop in Java Using Lambdas for iteration Nested classes in collections Empty collections Singleton collections Synchronized collections Checked collections Immutable collections Wrapper class Conclusion Exercise Answers 5. List Interface and Implementations

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Introduction Structure Objectives List interface ArrayList implementation Use cases for ArrayList Performance considerations Custom implementation of ArrayList LinkedList implementation Internal structure of LinkedList Performance considerations for LinkedList Custom LinkedList implementation Vector implementation Synchronization in lists Collections.synchronizedList() CopyOnWriteArrayList Unmodifiable collections Checked collections Advantages of using checked collections Conclusion Exercise Answers 6. Map Interface and Implementations Introduction Structure Objectives Map interface HashMap implementation