Java Arrays

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  Data Structures and Program Design Using Java

  A Self-Teaching Introduction

  • D. Malhotra, N. Malhotra(Authors)
  • 2020(Publication Date)
  • Mercury Learning and Information

    (Publisher)

  3

  ARRAYS

  3.1  Introduction

  In the previous chapter we studied the basics of programming in data structures and Java in which we aimed to design good programs, where a good program refers to a program which runs correctly and efficiently by occupying less space in the memory, and also takes less time to run and execute. Undoubtedly, a program is said to be efficient when it executes with less memory space and also in minimal time. In this chapter, we will learn about the concept of arrays. An array is a user-defined data type that stores related information together. Arrays are discussed in detail in the following sections.

  3.2  Definition of an Array

  An array is a collection of homogeneous (similar) types of data elements in contiguous memory. An array is a linear data structure, because all elements of the array are stored in linear order. Let us take an example in which we have ten students in a class, and we have been asked to store the marks of all ten students; then we need a data structure known as an array.

  Figure 3.1. Representation of an array of ten elements.

  In the previous example, the data elements are stored in the successive memory locations and are identified by an index number (also known as the subscript), that is, Ai or A[i]. A subscript is an ordinal number which is used to identify an element of the array. The elements of an array have the same data type, and each element in an array can be accessed using the same name.

   

  Frequently Asked Questions

  1. What is an array? How can we identify an element in the array?

  Ans: An array is a collection of homogeneous (similar) types of data elements in contiguous memory. An element in an array can be identified by its index number, which is also known as a subscript.

  3.3  Array Declaration

  We know that all variables must be declared before they are used in the program. Therefore, the same concept also holds with array variables. An array must be declared before it is used. During the declaration of an array, the size of the array has to be specified. Declaring an array involves the following specifications:

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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)

  In this chapter, we will introduce the concept of an array and the powerful features of the construct that make it a part of most programs. These features include the ability to store and retrieve large data sets, and, when combined with the concept of a loop, these data sets can be processed with only a few instructions. Array processing algorithms such as sorting, searching, and copying will be discussed and implemented, as will algorithms introduced in Chapter 4 for inserting and deleting items stored in a disk text file. We will also explore the API methods that implement many of the classical array processing algorithms.

  One-dimensional arrays, which can be used to store a list of items, will be discussed as well as multi-dimensional arrays, and we will use two-dimensional arrays to organize data in tables as rows and columns.

  After successfully completing this chapter you should:

  • Understand the advantages and importance of using arrays

  • Be familiar with the Java memory model used to store arrays

  • Be able to construct and use arrays of primitives and objects

  • Understand and be able to implement the algorithms used to search an array, sort it, and find the minimum and maximum values stored in it

  • Be familiar with and be able to use the array-processing methods in the API

  • Understand the concept of parallel arrays and use them to process data sets

  • Know how to use arrays to insert, delete, or update data items stored in a disk file

  • Be able to apply array techniques to game programs

  6.1 THE ORIGIN OF ARRAYS

  The machines we call computers received their name because the first operational versions of these machines were primarily used by mathematicians to perform rapid computations on large data sets. They were machines whose task was to compute; they were computers. However, long before computers were operational, mathematicians were using subscripted variables, such as x2 or x4

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  Introduction to Computational Modeling Using C and Open-Source Tools

  • Jose M. Garrido(Author)
  • 2013(Publication Date)
  • Chapman and Hall/CRC

    (Publisher)

  Chapter 8 Arrays 8.1 Introduction An array stores multiple values of data with a single name and most program-ming languages include facilities that support arrays. The individual values in the array are known as elements . Many programs manipulate arrays and each one can store a large number of values in a single collection. To refer to an individual element of the array, an integer value or variable known as the array index is used after the name of the array. The value of the index repre-sents the relative position of the element in the array. Figure 8.1 shows an array with 13 elements. This array is a data structure with 13 cells, and each cell contains an element value. In the C programming language, the index values start with 0 (zero). FIGURE 8.1: A simple array. To use arrays in a C program the following steps are carried out: 1. Declare the array with appropriate name, size, and type 2. Assign initial values to the array elements 3. Access or manipulate the individual elements of the array In C, an array is basically a static data structure because once the array is de-clared, its size cannot be changed. The size of an array is the number of elements it can store. An array can also be created at execution time using pointers. A simple array has one dimension and is considered a row vector or a column vector. To manipulate the elements of a one-dimensional array, a single index is re-quired. A vector is a single-dimension array and by default it is a row vector. A matrix is a two-dimensional array and the typical form of a matrix is an array with data items organized into rows and columns. In this array, two indexes are used: one index to indicate the column and one index to indicate the row. Figure 8.2 shows 99 100 Introduction to Computational Modeling a matrix with 13 columns and two rows. Because this matrix has only two rows, the index values for the rows are 0 and 1. The index values for the columns are from 0 up to 12.

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  Programming Logic and Design, Introductory

  • Joyce Farrell(Author)
  • 2017(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Each of these real-life arrays helps you organize objects or information. You could store all your papers or receipts in one huge cardboard box, or find courses if they were printed randomly in one large book. However, using an organized storage and display system makes your life easier in each case. Similarly, an array provides an organized storage and display system for a program’s data. How Arrays Occupy Computer Memory When you declare an array, you declare a structure that contains multiple data items; each data item is one element of the array. Each element has the same data type, and each element occupies an area in memory next to, or contiguous to, the others. You can indicate the number of elements an array will hold—the size of the array—when you declare the array along with your other variables and constants. For example, you might declare an uninitialized, three-element numeric array named prices and an uninitialized string array of 10 employee names as follows: num prices[3] string employeeNames[10] When naming arrays, programmers follow the same rules as when naming variables. That is, array names must start with a letter and contain no embedded spaces. Additionally, many programmers observe one of the following conventions when naming arrays to make it more obvious that the name represents a group of items: • Arrays are often named using a plural noun such as prices or employeeNames. • Arrays are often named by adding a final word that implies a group, such as priceList, priceTable, or priceArray. 228 C H A P T E R 6 Arrays Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Each array element is differentiated from the others with a unique subscript, also called an index, which is a number that indicates the position of a particular item within an array.

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  Alice 3 in Action with Java™

  • Joel Adams(Author)
  • 2014(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  However, an array is not a good data structure for storing a sequence whose size changes, or where items are fre-quently inserted or removed. Instead, programmers use the list data structure, which we examine in Section 12.2. © Cengage Learning 2015 © Cengage Learning 2015 Copyright 2015 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Chapter 12 Arrays and Lists in Java 473 12.1.5 Multidimensional Arrays The arrays we have examined to this point have had just one property: length . Because length determines the amount of space an array needs, an array’s length is often referred to as its dimension , and the arrays we have seen so far have been one-dimensional arrays . Java also allows us to declare arrays with multiple dimensions. For example, many kinds of data can be naturally organized into a table that has two dimensions: rows and columns . To model such tables, we can build a class, as shown in Figure 12-11. 1 /** Table.java models a table with rows and columns.

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  Fundamentals of Python

  Data Structures

  • Kenneth Lambert(Author)
  • 2018(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  This chapter examines the data organization and concrete details of processing that are particular to arrays and linked structures. Their use in implementing various types of collections is discussed in later chapters. The Array Data Structure An array represents a sequence of items that can be accessed or replaced at given index positions. You are probably thinking that this description resembles that of a Python list. In fact, the data structure underlying a Python list is an array. Although Python programmers would typically use a list where you might use an array, the array rather than the list is the primary implementing structure in the collections of Python and many other programming languages. Therefore, you need to become familiar with the array way of thinking. Some of what this chapter has to say about arrays also applies to Python lists, but arrays are much more restrictive. A programmer can access and replace an array’s items at given positions, examine an array’s length, and obtain its string representation—but that’s all. The programmer cannot add or remove positions or make the length of the array larger or smaller. Typically, the length or capacity of an array is fixed when it is created. Python’s array module does include an array class, which behaves more like a list but is limited to storing numbers. For purposes of the discussion that follows, you will define a new class named Array that adheres to the restrictions mentioned earlier but can hold items of any type. Ironically, this Array class uses a Python list to hold its items. The class defines methods that allow clients to use the subscript operator [], the len function, the str function, and the for loop with array objects. The Array methods needed for these operations are listed in Table 4-1. The variable a in the left column refers to an Array object.

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  A Textbook of Data Structures and Algorithms, Volume 1

  Mastering Linear Data Structures

  • G. A. Vijayalakshmi Pai(Author)
  • 2022(Publication Date)
  • Wiley-ISTE

    (Publisher)

  3 Arrays 3.1. Introduction In Chapter 1, an abstract data type (ADT) was defined to be a set of data objects and the fundamental operations that can be performed on this set. In this regard, an array is an ADT whose objects are a sequence of elements of the same type, and the two operations performed on it are store and retrieve. Thus, if a is an array, the operations can be represented as STORE (a, i, e) and RETRIEVE (a, i), where i is termed the index and e is the element that is to be stored in the array. These functions are equivalent to the programming language statements a[i ]:= e and a[i], where i is termed subscript and a is termed array variable name in programming language parlance. Arrays can be one-dimensional, two-dimensional, three-dimensional or in general multidimensional. Figure 3.1 illustrates a one-dimensional and two-dimensional array. It may be observed that while one-dimensional arrays are mathematically likened to vectors, two-dimensional arrays are likened to matrices. In this regard, two-dimensional arrays also have the terminologies of rows and columns associated with them. Figure 3.1. Examples of arrays 46 A Textbook of Data Structures and Algorithms 1 In Figure 3.1, A[1:5] refers to a one-dimensional array where 1 and 5 are referred to as the lower and upper indexes or the lower and upper bounds of the index range, respectively. Similarly, B[1:3, 1:2] refers to a two-dimensional array where 1, 3 and 1, 2 are the lower and upper indexes of the rows and columns, respectively. Additionally, each element of the array, namely, A[i] or B[i, j], resides in a memory location also called a cell. Here, the cell refers to a unit of memory and is machine dependent. 3.2. Array operations An array, when viewed as a data structure, supports only two operations, namely: (i) storage of values, that is, writing into an array (STORE (a, i, e)); (ii) retrieval of values, that is, reading from an array (RETRIEVE (a, i)).

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  Microsoft® Visual C# 2015

  An Introduction to Object-Oriented Programming

  • Joyce Farrell, , , (Authors)
  • 2015(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 260 C H A P T E R 6 Using Arrays Chapter Summary • An array is a list of data items, all of which have the same type and the same name but are distinguished from each other using a subscript or index. You declare an array variable by inserting a pair of square brackets after the type and reserve memory for an array by using the keyword new . Any array’s elements are numbered 0 through one less than the array’s length. In C#, arrays are objects that derive from a class named System.Array . An array’s elements are initialized to default values. To initialize an array to nondefault values, you use a list of values that are separated by commas and enclosed within curly braces. • Arrays are most powerful when variable subscripts are used to process array elements. Any array subscript must remain in the range of 0 through Length - 1 . The Length property automatically holds an array’s length. You can use the foreach statement to cycle through every array element without using subscripts. • When you want to determine whether a variable holds one of many possible valid values, you can compare the variable to a list of values in an array. You can set up a parallel array to access additional information. • The BinarySearch() method finds a requested value in a sorted array. The method returns –1 if the value is not found in the array; otherwise, it returns the array position of the sought value.

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  Elementary Synchronous Programming

  in C++ and Java via algorithms

  • Ali S. Janfada(Author)
  • 2019(Publication Date)
  • De Gruyter Oldenbourg

    (Publisher)

  https://doi.org/10.1515/9783110616484-008 8 One-dimensional arrays 8.1 vectors In previous chapters, we addressed independent and non-homonymous variables in algorithm writing and programming. Now, we start working with variables named arrays which include one or more indices. These variables have the same name but different indices. In the process of solving certain problems, we have to deal with a large number of variables having similar behaviours in the program. In these situa-tions, defining all the variables independently consumes the time of the algorithm, increases its size and thus makes it useless. Therefore, we use arrays which have ho-monymous variables and different indices in order to overcome this problem. An im-portant advantage of using arrays is in object-oriented programming: arrays, as the predefined objects, pass by the reference. In the present chapter, we concentrate on one-dimensional arrays and remove the phrase “one-dimensional”. This type of array is occasionally regarded as a vector or a list. For example, an array of eight entries is illustrated in the following diagram. u u u u u u u u u[1] u[2] u[3] u[4] u[5] u[6] u[7] u[8] As shown, eight different variables exists in this diagram all having the same name while different indices. In theoretical studies, these variables are written as u 1 , u 2 , …, u 8 . All of the entries of an array should be of the same data type which is then asso-ciated with the array data type. For instance, an array is integer if all of its entries are integers. The declaration of arrays in programming is as follows. declaration of arrays in C++: declaration of arrays in Java: data type array name [ array length ] ; data type ˽ array name []=new ˽ data type [ array length ]; For example, the statement in C++: in Java: int u[8]; int u[]=new int[8]; declares the variable u as a one-dimensional integer array with a length of 9. As re-gards the entry u n in programs, we write u[n] .

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  C# Programming

  From Problem Analysis to Program Design

  • Barbara Doyle, , , (Authors)
  • 2015(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  © zeljkodan/Shutterstock.com A RRAYS IN THIS CHAPTER, YOU WILL: ? Learn array basics. ? Declare arrays and perform compile-time initialization of array elements ? Access elements of an array ? Become familiar with methods of the Array class ? Write methods that use arrays as parameters ? Write classes that include arrays as members and instantiate user-defined array objects ? Work through a programming example that illustrates the chapter’s concepts 7 CHAPTER Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 400 | Chapter 7: Arrays In previous chapters, you were introduced to the basics of programming. You learned about the three programming constructs of simple sequence, selection, and itera-tion. You learned to handle data and declare memory locations to store and access values using an identifier. In this chapter, you will discover how to work with col-lections of data that are referenced by a single identifier name. You will learn about one type of collection, called an array, which is similar to a vector in mathematics or cells in a spreadsheet in that each entry can be referenced by the location of the item in the collection. You will create arrays that can hold multiple data values. Using an index to reference the location of the item, you will learn how to access single values and iterate through collections to process all the values. You will learn about special properties and methods of the .NET Array class and learn how to define arrays of user-defined objects.

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