Java Collections Framework

10 Key excerpts on "Java Collections Framework"

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  eBook - ePub

  Java Professional Interview Guide

  Learn About Java Interview Questions and Practise Answering About Concurrency, JDBC, Exception Handling, Spring, and Hibernate

  • Mandar Maheshwar Jog(Author)
  • 2021(Publication Date)
  • BPB Publications

    (Publisher)

  HAPTER 8

  Collections

  Introduction

  Java is an object-oriented programming language. Software created using Java comprises of a number of objects that communicate with each other. It is always essential to group these objects together so as to perform some common operations on these objects. Normally, such operations need to be performed manually by a developer repetitively. To reduce such effort, Java introduced the collection framework, which consists of predefined data structures and algorithm, which can be applied on an object. The collection framework is essentially a group of different interfaces and their implementation classes using which one can group the objects based on different scenarios. Every interface on its own facilitates different functionalities to a group of objects based on which objects are arranged or traversed. Such functionalities give flexibility to the developers to use objects in an application to their full capacity to achieve the desired result. Sometimes, the developers are in a need of objects that are ordered; sometimes, they want the same object group without duplicates, or sometimes, the same object group in some sorted order. The collection framework provides all such solutions to the developers.

  Structure

  Understanding the collection framework is often assumed to be complex. It consists of a number of interfaces, sub-interfaces, and their implementation classes. In this chapter, we will cover the different aspects of the Collection framework as:

  • What is the need for the Collection framework?
  • Different Collection interfaces:
    • List
    • Set
    • Queue
    • Map
  • Utility classes like Collections and Arrays

  Objective

  Every interface in Collection is defined to achieve a specific functionality. To remember such a big API is not an easy task. And, because of its importance in real-time projects, Collection is one of the most favorite topics in the Java interview process. As mentioned, the Collection Framework API is huge. So, covering each and every class is not possible or, in fact, not required as far as the interview process is concerned. But, for sure, in this chapter, you will learn how to answer almost every important question, right from the concept to implementation so that you will succeed in an interview. You will able to master the different collection types like List, Set, Queue, and Map, and their implementations.

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  Introduction to Programming

  Learn to program in Java with data structures, algorithms, and logic

  • Nick Samoylov(Author)
  • 2018(Publication Date)
  • Packt Publishing

    (Publisher)

  Java Collections

  This chapter will help the reader to become more familiar with the most commonly used Java collections. The code examples illustrate their functionality and allow an experimentation that emphasizes the difference between different collection types and their implementations.

  In this chapter, we will cover the following topics:

  • What are collections?
  • List and ArrayList
  • Set and HashSet
  • Map and HashMap
  • Exercise – EnumSet methods

  Passage contains an image

  What are collections?

  When you read about the Java Collection Framework, you may assume there is something special about such an assemblage. Meanwhile, the word framework is quite overloaded and misused, as the word technology is one we have refused to use already. In the English language, the word framework means a basic structure underlying a system, concept, or text. In computer programming, a framework is a software system constructed so that its functionality can be customized by additional user-written code or configuration settings in order to fit the application-specific requirements.

  But then we look closer into the content of the Java Collection Framework and realize that all its members belong to the java.util package, which is part of the Java Class Library, or Java standard library, as we have described it in the previous chapter. And, at the other extreme, the graphic user interfaces in the packages java.awt, javax.swing, or

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  eBook - PDF

  Ivor Horton's Beginning Java 2

  • Ivor Horton(Author)
  • 2005(Publication Date)
  • Wrox

    (Publisher)

  600 Chapter 13 14 The Collections Framework In this chapter you’ll look at the Java Collections Framework, which consists of generic types that represent sets of collection classes. These generic types are defined in the java.util package, and they provide you with a variety of ways for structuring and managing collections of objects in your programs. In particular, the collection types enable you to deal with situations where you don’t know in advance how many objects you’ll need to store, or where you need a bit more flexibility in the way in which you access an object from a collection than the indexing mechanism provided by an array. In this chapter you will learn: ❑ What sets, sequences, and maps are, and how they work ❑ What a Vector collection object is and how to use Vector objects in your programs ❑ How to manage Vector objects so that storing and retrieving elements is typesafe ❑ What a Stack collection is and how you use it ❑ How you use the LinkedList collections ❑ How you store and retrieve objects in a hash table represented by a HashMap object ❑ How you can generate hashcodes for your own class objects Understanding the Collections Framework The Java Collections Framework is a set of generic types that you use to create collection classes that support various ways for you to store and manage objects of any kind in memory. As I’m sure you appreciate from the previous chapter, a collection class is simply a class that organizes a set of objects of a given type in a particular way, such as in a linked list or a pushdown stack. The major- ity of types that make up the collections framework are defined in the java.util package. Using a generic type for your collections of objects means that you get static checking by the compiler for whatever types of objects you want to manage. This ensures that you do not inadvertently attempt to store objects of the wrong type in a collection.

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  The Java Workshop

  A Practical, No-Nonsense Introduction to Java Development

  • David Cuartielles, Andreas Göransson, Eric Foster-Johnson(Authors)
  • 2019(Publication Date)
  • Packt Publishing

    (Publisher)

  4. Collections, Lists and Java's Built-In APIs

  Overview

  This chapter introduces you to the powerful Java Collections Framework, which is used to store, sort, and filter data. It will first take you through the structure of the built-in Collections Application Programming Interface (API ), the Java Collections Framework, which will simplify your dealings with complex data structures and allow you to use and create APIs with minimal effort. Through this framework, you will examine the relationship between lists and arrays, and learn to populate lists from arrays. Finally, in this chapter's final activity, you will create and complete a program in which you will be asked to perform standard operations on data stored in sets, lists, and maps in preparation for future chapters.

  Introduction

  Java comes with a built-in Collections API, allowing you to manipulate data structures with very little effort. A collection is an object that contains multiple elements. Collections are used to store, share, process, and communicate aggregated data. We call this system the Java Collections Framework .

  As part of this framework, there are different components that are used to optimize our interaction with the actual data:

  • Interfaces : Abstract data types that represent collections
  • Implementations : Specific implementations of the collection interfaces
  • Algorithms : Polymorphic methods used to process the data within a collection for operations such as sorting and searchingNote
    Other programming languages have their own collection frameworks. For example, C++ has the Standard Template Library (STL

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  eBook - PDF

  Brief Java

  Early Objects

  • Cay S. Horstmann(Author)
  • 2019(Publication Date)
  • Wiley

    (Publisher)

  511 C H A P T E R 15 THE Java Collections Framework C H A P T E R G O A L S To learn how to use the collection classes supplied in the Java library To use iterators to traverse collections To choose appropriate collections for solving programming problems To study applications of stacks and queues C H A P T E R C O N T E N T S © nicholas belton/iStockphoto. 15.1 AN OVERVIEW OF THE COLLECTIONS FRAMEWORK 512 15.2 LINKED LISTS 514 C&S Standardization 519 15.3 SETS 520 PT 1 Use Interface References to Manipulate Data Structures 524 15.4 MAPS 525 ST 1 Updating Map Entries 527 HT 1 Choosing a Collection 527 WE1 Word Frequency 528 ST 2 Hash Functions 529 15.5 STACKS, QUEUES, AND PRIORITY QUEUES 531 15.6 STACK AND QUEUE APPLICATIONS 534 ST 3 Reverse Polish Notation 542 WE2 Simulating a Queue of Waiting Customers 543 512 If you want to write a program that collects objects (such as the stamps to the left), you have a number of choices. Of course, you can use an array list, but computer scientists have invented other mechanisms that may be better suited for the task. In this chapter, we introduce the collection classes and interfaces that the Java library offers. You will learn how to use the Java collection classes, and how to choose the most appropriate collection type for a problem. 15.1 An Overview of the Collections Framework When you need to organize multiple objects in your program, you can place them into a collection. The ArrayList class that was introduced in Chapter 7 is one of many collection classes that the standard Java library supplies. In this chapter, you will learn about the Java Collections Framework, a hierarchy of interface types and classes for collecting objects. Each interface type is implemented by one or more classes (see Figure 1). At the root of the hierarchy is the Collection interface. That interface has methods for adding and removing elements, and so on.

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  eBook - PDF

  Big Java

  Late Objects

  • Cay S. Horstmann(Author)
  • 2016(Publication Date)
  • Wiley

    (Publisher)

  15 C H A P T E R 691 THE Java Collections Framework To learn how to use the collection classes supplied in the Java library To use iterators to traverse collections To choose appropriate collections for solving programming problems To study applications of stacks and queues CHAPTER GOALS CHAPTER CONTENTS 15.1 AN OVERVIEW OF THE COLLECTIONS FRAMEWORK 692 15.2 LINKED LISTS 695 C&S Standardization 700 15.3 SETS 701 PT 1 Use Interface References to Manipulate Data Structures 705 15.4 MAPS 706 J8 1 Updating Map Entries 708 HT 1 Choosing a Collection 708 WE 1 Word Frequency ST 1 Hash Functions 710 15.5 STACKS, QUEUES, AND PRIORITY QUEUES 712 15.6 STACK AND QUEUE APPLICATIONS 715 WE 2 Simulating a Queue of Waiting Customers VE 1 Building a Table of Contents ST 2 Reverse Polish Notation 723 © nicholas belton/iStockphoto. 692 If you want to write a program that collects objects (such as the stamps to the left), you have a number of choices. Of course, you can use an array list, but computer scientists have invented other mechanisms that may be better suited for the task. In this chapter, we introduce the collection classes and interfaces that the Java library offers. You will learn how to use the Java collection classes, and how to choose the most appropriate collection type for a problem. 15.1 An Overview of the Collections Framework When you need to organize multiple objects in your program, you can place them into a collection . The ArrayList class that was introduced in Chapter 6 is one of many collection classes that the standard Java library supplies. In this chapter, you will learn about the Java Collections Framework , a hierarchy of interface types and classes for collecting objects. Each interface type is implemented by one or more classes (see Figure 1). At the root of the hierarchy is the Collection interface. That interface has methods for adding and removing elements, and so on.

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  eBook - PDF

  Java Concepts

  Late Objects

  • Cay S. Horstmann(Author)
  • 2016(Publication Date)
  • Wiley

    (Publisher)

  15 C H A P T E R 691 THE Java Collections Framework To learn how to use the collection classes supplied in the Java library To use iterators to traverse collections To choose appropriate collections for solving programming problems To study applications of stacks and queues CHAPTER GOALS CHAPTER CONTENTS 15.1 AN OVERVIEW OF THE COLLECTIONS FRAMEWORK 692 15.2 LINKED LISTS 695 C&S Standardization 700 15.3 SETS 701 PT 1 Use Interface References to Manipulate Data Structures 705 15.4 MAPS 706 J8 1 Updating Map Entries 708 HT 1 Choosing a Collection 708 WE 1 Word Frequency ST 1 Hash Functions 710 15.5 STACKS, QUEUES, AND PRIORITY QUEUES 712 15.6 STACK AND QUEUE APPLICATIONS 715 WE 2 Simulating a Queue of Waiting Customers VE 1 Building a Table of Contents ST 2 Reverse Polish Notation 723 © nicholas belton/iStockphoto. 692 If you want to write a program that collects objects (such as the stamps to the left), you have a number of choices. Of course, you can use an array list, but computer scientists have invented other mechanisms that may be better suited for the task. In this chapter, we introduce the collection classes and interfaces that the Java library offers. You will learn how to use the Java collection classes, and how to choose the most appropriate collection type for a problem. 15.1 An Overview of the Collections Framework When you need to organize multiple objects in your program, you can place them into a collection. The ArrayList class that was introduced in Chapter 6 is one of many collection classes that the standard Java library supplies. In this chapter, you will learn about the Java Collections Framework, a hierarchy of interface types and classes for collecting objects. Each interface type is implemented by one or more classes (see Figure 1). At the root of the hierarchy is the Collection interface. That interface has methods for adding and removing elements, and so on.

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  Programming Essentials Using Java

  A Game Application Approach

  • William McAllister, S. Jane Fritz(Authors)
  • 2017(Publication Date)
  • Mercury Learning and Information

    (Publisher)

  For example, one program processes a collection of maintenance work orders, another a collection of student transcript objects, and another a collection of personnel records. Although the objects these programs store and process are instances of different classes, programs of this type share a common set of operations that are usually performed on the objects. For example, each of these programs has to add objects to their collection, as well as retrieve them from their collection. Two other common operations on collections of objects are removing an object from the collection, and modifying an object in the collection. To facilitate the storage and processing of information groups such as these (i.e., work orders, transcripts, and personnel records), the Java API provides a group of collection classes. Unlike the classes we have encountered thus far in this textbook, these classes are coded in a generic way. A single instance of one of these classes, a collection object, can be declared to store an information group consisting of instances of any class. In addition, each collection class implements one of the classic storage schemes that facilitate the common operations performed on groups of objects. The collection classes are part of the API Collections Framework. The framework also includes: •  A set of interfaces that define the generic signatures and general functionality of methods common to the collection classes, such as the methods add and remove that place an item into and eliminate an item from a collection •  A class named Collections that implements algorithms that efficiently perform common operations on collections of objects such as sort, binarySearch, min, and max whose names imply their functionality 10.2 THE FRAMEWORK INTERFACES Eight of the framework’s core collection interfaces are shown in blue in Figure 10.1. They are divided into two groups: those that extend the interface Map and those that extend the interface Collection

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  eBook - ePub

  Learn Java 17 Programming

  • Nick Samoylov(Author)
  • 2022(Publication Date)
  • Packt Publishing

    (Publisher)

  Chapter 6 : Data Structures, Generics, and Popular Utilities

  This chapter presents the Java Collections Framework and its three main interfaces, List , Set , and Map , including a discussion and demonstration of generics. The equals() and hashCode() methods are also discussed in the context of Java collections. Utility classes for managing arrays, objects, and time/date values have corresponding dedicated sections too. After studying this chapter, you will be able to use all the main data structures in your programs.

  The following topics will be covered in this chapter:

  • List , Set , and Map interfaces
  • Collections utilities
  • Arrays utilities
  • Object utilities
  • The java.time package

  Let’s begin!

  Technical requirements

  To be able to execute the code examples provided in this chapter, you will need the following:

  • A computer with a Microsoft Windows, Apple macOS, or Linux operating system
  • Java Standard Edition (SE ) version 17 or later
  • An integrated development environment (IDE ) or your preferred code editor

  Instructions on how to set up a Java SE and IntelliJ IDEA editor were provided in Chapter 1 of this book, Getting Started with Java 17 . The files with code examples for this chapter are available on GitHub in the https://github.com/PacktPublishing/Learn-Java-17-Programming.git repository, in the examples/src/main/java/com/packt/learnjava/ch06_collections folder.

  List, Set, and Map interfaces

  The Java Collections Framework consists of classes and interfaces that implement a collection data structure. Collections are similar to arrays in that they can hold references to objects and can be managed as a group. The difference is that arrays require their capacity to be defined before they can be used, while collections can increase and decrease their size automatically as needed. You just add or remove an object reference to a collection, and the collection changes its size accordingly. Another difference is that collections cannot have their elements be primitive types, such as short , int , or double . If you need to store such type values, the elements must be of a corresponding wrapper type, such as Short , Integer , or Double

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  Programming Fundamentals Using JAVA

  A Game Application Approach

  • William McAllister, S. Jane Fritz(Authors)
  • 2021(Publication Date)
  • Mercury Learning and Information

    (Publisher)

  HAPTER 13

  GENERICS AND THE API COLLECTION FRAMEWORK

  13.1 Overview

  13.2 Generic Methods

  13.3 Generic Classes

  13.4 The API Collections Framework

  13.5 Streams and Functional Programming

  13.6 Chapter Summary

  In this chapter

  In this chapter, we extend our knowledge of methods and classes by incorporating the feature of generics into them. This will make the methods and classes we write more reusable and less error prone. A generic method can be passed arguments of different types, and the types of the data members of a generic class can be specified when an instance in the class is created. These powerful features can be used to write classes called data structures that can store, fetch, and process a set of any type of objects. Data structures such as lists, queues, stacks, sets, and hash maps will be discussed.

  A set of highly reusable generic methods, interfaces, and classes make up the Java Collection Framework. The methods implement classic computer algorithms, and the classes implement commonly used techniques for efficiently processing large data sets. We will learn the functionality of these methods and classes and how to incorporate them into the programs we write. In addition, we will discuss two groupings of classes included in the framework and the advantages of the Map grouping that can be used to efficiently locate a particular object in a large data set by simply specifying a key value that has been associated with the object.

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