java array programming

8/12/2019 java array programming

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Chapter III

Arrays in Java

Java ProgrammingCOSC 450

Dr. Mohamad EL ABED


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Chapter III - Objectives

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To use the array data structure to represent lists and tables ofvalues

To define an array, initialize an array and refer to individual

elements of an array

To pass arrays to functions

To use arrays to store, sort and search lists and tables of

values

To define and manipulate multiple-subscripted arrays


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Chapter III - Outline

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Arrays: Definition and Declaration

The Length of an Array

Initializing Arrays with Input Values

Enhanced for Statement

Searching Arrays

Multidimensional Arrays

Variable-Length Argument Lists


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Definition An arrayis a group of memory locations related by the fact

that they all have the same nameand the same type

You can make an array of any type

int, double, String, etc.

Declaration

Type[] table_name = newType[length]

int [] values = newint [5];


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Example

myList[0] references the first elementin the array

myList[9] references the last elementin the array


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To create an array of a given size, use the operator new:


Or you may use a variable to specify the size:

int size = 12;

int [] values = newint [size];


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Searching Arrays




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Once an array is created, its size is fixed. It cannot be changed.

You can find its size using length function

Example


values.length returns 25


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Searching Arrays




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Usingjava.util.Scanner


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Searching Arrays




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The enhanced for statement iterates through the elements of

an array withoutusing a counter, thus avoiding the possibility

of stepping outside the array

Syntaxfor (elementType value: arrayRefVar) {

// Process the value

}

Example


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Searching Arrays




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Searching Arrays

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Programmers often work with large amounts of data;

It is necessary to determinewhether an array containsa value

that matches a certain key value

The process of finding a particular element of an array is called

searching

o Linear search

o Binary search


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Searching an Array with Linear Search

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The linear searchcompares each element of the array with

the search key

Since the array is not in any particular order, its just as likely

that the value will be found in the firstelement as in the last


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Problem Statement

Write a function that returns 1 if a given array contains a key

value passed by the function parameter; 0 otherwise


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Linear Search Technique disadvantages

The linear searchingmethod works well for smallor unsorted

arrays

However, for largearrays linear searching is inefficient

If the array is sorted, the high-speed binary searchtechnique

can be used


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Searching an Array with Binary Search

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The binary searchalgorithm eliminatesfrom consideration

one-halfof the elements in a sortedarray after each comparison

The algorithm locatesthe middleelement of the array and

comparesit to thekey value


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Example 1

2 1 5 4 7Array:

Key value: 7

Sorted Array:

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1 2 3 4 5 7 11

The array contains 7


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Example 2

2 1 5 4 7Array:

Key value: 6

Sorted Array:

11 3

1 2 3 4 5 7 11

The array do not contains 6


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Linear Search vs. Binary Search

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In a worstcase-scenario, searchingan array of 1024 elements

takes:

o 1024 comparisons using a linear search

o 10 comparisons using a binary search


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Searching Arrays




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Arrays in C++ can have multiplesubscripts

A common use of multidimensional arrays is to represent

tablesof values consisting of information arranged in rows

and columns

To identify a particular table element, we must specify two

subscripts: The firstidentifies the elements rowand the

secondidentifies the elements column


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In general, an array with m rows and n columns is called anm-by-n array

An example of double-subscripted array

int[][] a = newint[3][4];


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Or you may use variables to specify the 2D array:


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Uneven rows

One consequence of 2D arrays is that each row can be a

different size

Example Lower Triangular array


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Searching Arrays




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With variable-length argument lists, you can create methods

that receive an unspecified number of arguments

A type followed by an ellipsis () in a methods parameter list

indicates that the method receives a variablenumber of

arguments of that particular type


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Example


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Common Programming Error

Placing an ellipsisin the middle of a parameter list is a syntax

error

An ellipsismay be placed only at the end of the parameter

list


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End of Chapter III

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