Java Set Interface

6 Key excerpts on "Java Set Interface"

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  eBook - PDF

  Data Structures

  Abstraction and Design Using Java

  • Elliot B. Koffman, Paul A. T. Wolfgang(Authors)
  • 2021(Publication Date)
  • Wiley

    (Publisher)

  The Set Abstraction The Java API documentation for the interface java.util.Set describes the Set as follows: A collection that contains no duplicate elements. More formally, sets contain no pair of elements e1 and e2 such that e1.equals(e2), and at most one null element. As implied by its name, this interface models the mathematical set abstraction. S e t s a n d M a p s 7.1 Sets and the Set Interface 7.2 Maps and the Map Interface 7.3 Hash Tables 7.4 Implementing the Hash Table 7.5 Implementation Considerations for Maps and Sets 7.6 Additional Applications of Maps Case Study: Implementing a Cell Phone Contact List Case Study: Completing the Huffman Coding Problem 7.7 NavigableSets and NavigableMaps 7.8 Skip-Lists 324 Chapter 7 Sets and Maps What mathematicians call a set can be thought of as a collection of objects. There is the addi- tional requirement that the elements contained in the set are unique. For example, if we have the set of fruits {"apples", "oranges", "pineapples"} and add "apples" to it, we still have the same set. Also, we usually want to know whether or not a particular object is a member of the set rather than where in the set it is located. Thus, if s is a set, we would be interested in the expression s.contains("apples") which returns the value true if "apples" is in set s and false if it is not. We would not have a need to use a method such as s.indexOf("apples") which might return the location or position of "apples" in set s. Nor would we have a need to use the expression s.get(i) where i is the position (index) of an object in set s. We assume that you are familiar with sets from a course in discrete mathematics. Just as a review, however, the operations that are performed on a mathematical set are testing for membership (method contains), adding elements, and removing elements. Other common operations on a mathematical set are set union (A ∪ B), set intersection (A ∩ B), and set differ- ence (A − B).

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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)

  STL ). Java boasts simplicity when it comes to its collection framework.

  Using the collections framework has many benefits, including a reduction in the complexity of creating programs that deal with data structures, an increase in the performance of programs, a simplification of API creation and use, and an increase in the reuse of functioning software.

  The collections framework is relevant even when handling data that can be accessed by several processes simultaneously, as this would be the case in multithreaded programming scenarios. However, it is not the intention of this chapter to deal with concurrent programming.

  The Collections API comes with five main interfaces:

  • Set : A collection that contains no duplicates
  • List : An ordered collection or sequence, allowing for duplicates
  • Queue : A collection that sorts data in the order of its arrival, typically handled as a First In First Out (FIFO ) process
  • Deque : Essentially a queue that allows for data insertion at both ends, meaning that it can be handled both as FIFO and Last In First Out (LIFO )
  • Map : Relates keys—which must be unique—to values

  In this chapter, we will define the main interfaces (lists, sets, and maps), and explore examples of their respective uses. The framework has even more interfaces than the ones listed previously, but the others are either just variations of those listed or are outside the scope of this chapter. Furthermore, we will look at how arrays work in much more depth than we have previously.

  The definition of a simple collection—in this case, a specific type of set would be as follows: Set mySet = new HashSet(); Note The different available classes for sets, lists, queues, deques, and maps are named after the interfaces. The different classes present different properties, as we will see later in the chapter.

  Arrays

  Arrays are part of the collections framework. There are some static methods that can be used to manipulate arrays. The operations you can perform are creating, sorting, searching, comparing, streaming, and transforming arrays. You were introduced to arrays in Chapter 2 , Learning the Basics

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  Java Concepts

  Late Objects

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

    (Publisher)

  If you do the latter, other programmers may have a hard time understanding your code because they aren’t familiar with your classes. Vorob’yev/iStockphot © Denis Vorob’yev/iStockphoto. 15.3 Sets 701 15.3 Sets As you learned in Section 15.1, a set organizes its values in an order that is optimized for efficiency, which may not be the order in which you add elements. Inserting and removing elements is more efficient with a set than with a list. In the following sections, you will learn how to choose a set implementation and how to work with sets. 15.3.1 Choosing a Set Implementation The Set interface in the standard Java library has the same methods as the Collection interface, shown in Table 1. However, there is an essential difference between arbi- trary collections and sets. A set does not admit duplicates. If you add an element to a set that is already present, the insertion is ignored. The HashSet and TreeSet classes implement the Set interface. These two classes pro- vide set implementations based on two different mechanisms, called hash tables and binary search trees. Both implementations arrange the set elements so that finding, adding, and removing elements is efficient, but they use different strategies. The basic idea of a hash table is simple. Set elements are grouped into smaller col- lections of elements that share the same characteristic. You can imagine a hash set of books as having a group for each color, so that books of the same color are in the same group. To find whether a book is already present, you just need to check it against the books in the same color group. Actually, hash tables don’t use colors, but integer values (called hash codes) that can be computed from the elements. In order to use a hash table, the elements must have a method to compute those integer values. This method is called hashCode. The elements must also belong to a class with a properly defined equals method (see Section 9.5.2).

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  eBook - PDF

  Big Java

  Late Objects

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

    (Publisher)

  If you do the latter, other programmers may have a hard time understanding your code because they aren’t familiar with your classes. Vorob’yev/iStockphot © Denis Vorob’yev/iStockphoto. 15.3 Sets 701 15.3 Sets As you learned in Section 15.1, a set organizes its values in an order that is optimized for efficiency, which may not be the order in which you add elements. Inserting and removing elements is more efficient with a set than with a list. In the following sections, you will learn how to choose a set implementation and how to work with sets. 15.3.1 Choosing a Set Implementation The Set interface in the standard Java library has the same methods as the Collection interface, shown in Table 1. However, there is an essential difference between arbi-trary collections and sets. A set does not admit duplicates. If you add an element to a set that is already present, the insertion is ignored. The HashSet and TreeSet classes implement the Set interface. These two classes pro-vide set implementations based on two different mechanisms, called hash tables and binary search trees . Both implementations arrange the set elements so that finding, adding, and removing elements is efficient, but they use different strategies. The basic idea of a hash table is simple. Set elements are grouped into smaller col-lections of elements that share the same characteristic. You can imagine a hash set of books as having a group for each color, so that books of the same color are in the same group. To find whether a book is already present, you just need to check it against the books in the same color group. Actually, hash tables don’t use colors, but integer values (called hash codes) that can be computed from the elements. In order to use a hash table, the elements must have a method to compute those integer values. This method is called hashCode . The elements must also belong to a class with a properly defined equals method (see Section 9.5.2).

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  eBook - PDF

  Brief Java

  Early Objects

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

    (Publisher)

  15.3 Sets As you learned in Section 15.1, a set organizes its values in an order that is optimized for efficiency, which may not be the order in which you add elements. Inserting and removing elements is more efficient with a set than with a list. In the following sections, you will learn how to choose a set implementation and how to work with sets. 15.3.1 Choosing a Set Implementation The Set interface in the standard Java library has the same methods as the Collection interface, shown in Table 1. However, there is an essential difference between arbi- trary collections and sets. A set does not admit duplicates. If you add an element to a set that is already present, the insertion is ignored. The HashSet and TreeSet classes implement the Set interface. These two classes pro- vide set implementations based on two different mechanisms, called hash tables and binary search trees. Both implementations arrange the set elements so that finding, adding, and removing elements is efficient, but they use different strategies. The HashSet and TreeSet classes both implement the Set interface. 15.3 Sets 521 The basic idea of a hash table is simple. Set elements are grouped into smaller collections of elements that share the same characteristic. You can imagine a hash set of books as having a group for each color, so that books of the same color are in the same group. To find whether a book is already present, you just need to check it against the books in the same color group. Actually, hash tables don’t use col- ors, but integer values (called hash codes) that can be computed from the elements. In order to use a hash table, the elements must have a method to compute those integer values. This method is called hashCode. The elements must also belong to a class with a properly defined equals method (see Sec- tion 9.5.2). Many classes in the standard library implement these methods, for example String, Integer, Double, Point, Rectangle, Color, and all the collection classes.

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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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