Chapter 6: Arrays and Strings

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Chapter 6 Arrays and Strings

• Introducing Arrays
• Declaring Arrays
• Creating Arrays
• Initializing Arrays
• Array of Objects
• Copying Arrays
• Multidimensional Arrays
• String , StringBuffer, and StringTokenizer
• Command-Line Parameters

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Introducing Arrays

• Array is a data structure that represents a
  collection of the same types of data.
• Java treats these arrays as objects.
• An Array of 10 Elementsof type double

double myList new double10
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Declaring Arrays

• datatype arrayname
• Example
• int myList
• datatype arrayname
• Example
• int myList

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Creating Arrays

• arrayName new datatypearraySize
• Example
• myList new double10

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Declaring and Creatingin One Step

• datatype arrayname new datatypearraySize
• double myList new double10
• datatype arrayname new datatypearraySize
• double myList new double10

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Initializing Arrays

• Using a loop
• for (int i 0 i lt myList.length i)
• myListi (double)i
• Declaring, creating, initializing in one step
• double myList 1.9, 2.9, 3.4, 3.5

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Example 6.2Using Arrays in Sorting

• Objective Use the selectionSort() method to
  write a program that will sort a list of double
  floating-point numbers.

TestSelectionSort
Run
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Example 6.3Testing Linear Search

• Objective Implement and test the linear search
  method by creating an array of 10 elements of int
  type randomly and then displaying this array.
  Prompt the user to enter a key for testing the
  linear search.

TestLinearSearch
Run
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Array of Objects

• Declaring and creating
• Circle circleArray new Circle10
• Initializing
• for (int i0 iltcircleArray.length i)
• circleArrayi new Circle()

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Copying Arrays

• Using a loop
• int sourceArray 2, 3, 1, 5, 10
• int targetArray new intsourceArray.length
• for (int i 0 i lt sourceArrays.length i)
• targetArrayi sourceArrayi

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The arraycopy Utility

• arraycopy(sourceArray, src_pos, targetArray,
  tar_pos, length)
• Example
• System.arraycopy(sourceArray, 0, targetArray, 0,
  sourceArray.length)

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Multidimensional Arrays

• int matrix new int1010
• or
• int matrix new int1010
• for (int i0 iltmatrix.length i)
• for (int j0 jltmatrixi.length j)
• matrixij (int)(Math.random()1000)

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Example 6.7Testing Multidimensional Arrays

• Objective Use two-dimensional arrays to create
  two matrices, and then add the two matrices.

TestMatrixAddition
Run
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The String Class

• Declaring a String
• String message "Welcome to Java!"
• String s new String()
• String Comparisons
• String Concatenation
• Substrings
• String Length
• Retrieving Individual Charactersin a String

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String Comparisons

• equals
• String s1 "Welcome"
• String s2 "welcome"
• if (s1.equals(s2))
• ...

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Substrings

• String is an immutable class its valuescannot
  be changed individually.
• String s1 "Welcome to Java"
• String s2 s1.substring(0,10) "HTML"

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Finding String Length

• Finding string length using the length() method
• message "Welcome"
• message.length() (returns 7)

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Retrieving Individual Characters in a String

• Do not use message0
• Use message.charAt(index)
• Index starts from 0

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The StringBuffer Class

• The StringBuffer class is an alternative to the
  String class. In general, a string buffer can be
  used wherever a string is used.StringBuffer is
  more flexible than String. You can add, insert,
  or append new contentsinto a string buffer.
  However, the value ofa string is fixed once the
  string is created.

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StringBuffer Constructors

• public StringBuffer()
• No characters, initial capacity 16 characters.
• public StringBuffer(int length)
• No characters, initial capacity specified by the
  length argument.
• public StringBuffer(String str)
• Represents the same sequence of charactersas
  the string argument. Initial capacity 16plus the
  length of the string argument.

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Appending New Contentsinto a String Buffer

• StringBuffer strBuf new StringBuffer()
• strBuf.append("Welcome")
• strBuf.append(' ')
• strBuf.append("to")
• strBuf.append(' ')
• strBuf.append("Java")

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The StringTokenizer Class Constructors

• StringTokenizer(String s, String delim, boolean
  returnTokens)
• StringTokenizer(String s, String delim)
• StringTokenizer(String s)

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The StringTokenizer Class Methods

• boolean hasMoreTokens()
• String nextToken()
• String nextToken(String delim)

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Example 6.9Testing StringTokenizer

• Objective Using a string tokenizer, retrieve
  words from a string and display them on the
  console.

TestStringTokenizer
Run
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Command-Line Parameters

• class TestMain
• public static void main(String args)
• ...
• java TestMain arg0, arg1, arg2, ..., argn

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ProcessingCommand-Line Parameters

• In the main method, get the arguments from
  args0, args1, ..., argsn, which corresponds
  to arg0, arg1, ..., argn in the command line.

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Example 6.10Using Command-Line Parameters

• Objective Write a program that will perform
  binary operations on integers. The program
  receives three parameters an operator and two
  integers.

TestCommandParameters
Run
Java TestCommandParameters 2 3
Run
Java TestCommandParameters - 2 3
Run
Java TestCommandParameters / 2 3