Announcements

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Announcements

• Final ExamTBD

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• public static void main(String args)
• final int ASIZE 5
• int intArray new intASIZE
• for(int i 0 i lt ASIZE i)
• intArrayi i
• System.out.println( intArray0)
• changeZero(intArray)
• System.out.println( intArray0)
• static void changeZero(int passedArray)
• passedArray0 1000

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Initializing Arrays

• char cArray3 'a', 'b', 'c'
• int iArray 1, 2, 3, 4
• double dArray 3.4, 5.67e4

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Two Dimensional Arrays

• char cArray new char1020
• int iArray new int10050
• cArray00 a
• cArray01 b
• cArray919 x
• iArray00 99
• iArray15 135
• iArray9949 0

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Math Class

• Contains Typical Math Methods
• In Package java.lang (i.e., automatically
  imported)
• Access using Math.math_thing
• Math.PI Math.E (log e 1)
• double pow (double base, double exp)
• double sqrt(double number)
• int round(double number)
• int abs( int number)
• min(number1,number2) and max(number1, number2)
• double random() //random number between 0.0 and
  1.0

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Tokenizing/Parsing

• Taking Apart a String and Separating It into
  Smaller Strings (i.e., tokens)
• Usually, Tokens are Items Separated by Whitespace
• Tokens Can Be Defined with Different Separators
• Parsing Takes Tokens and Applies Some
  Manipulation of Those Tokens

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StringTokenizer Class

• import java.util.
• String bigString This is a sentence.
• StringTokenizer st new StringTokenizer(bigString
  )
• while (st.hasMoreTokens())
• System.out.println(st.nextToken())
• // Displays This, is, a, and sentence. one
• // per line

8
Classes

• A Class Is an Object Type
• A Class Represents a Thing (e.g., employee,
  wrench, list, store, shopping cart, etc.)
• Service Class Class used by Other Programs
• Programmers Define Classes with Data Members (or
  Fields) and Methods
• Must Be Created in ClassName.java File
• Client Program Program using a class

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Access Modifiers

• Used to Identify What May Use Methods
• public any method may use (Usually methods)
• private only methods in same class may use
  (usually data members)

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Designing a Class

• Decide How It Will Be Used
• Decide on Interface (i.e., public representation,
  public methods)
• Decide on Implementation (i.e., private data and
  data manipulation)

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Example Class
Class Employee
firstName
lastName
salary
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Constructor

• Class Method of Same Name
• Example class Employee Method Employee()
• Called When Variable (invoking object) Declared
  (instantiated) of Class Type
• Initializes Instantiated Object
• May Have Multiple Constructors Each with
  Different Parameters

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• class Employee // Employee.java
• private String firstName
• private String lastName
• private double salary
• public Employee()
• // set attributes of invoking object
• firstName "NoFirstName"
• lastName "NoLastName"
• salary 0.0

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Accessor Methods

• Public Methods for Getting Attributes of Class

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• class Employee
• private String firstName
• private String lastName
• private double salary
• public Employee()
• firstName "NoFirstName"
• lastName "NoLastName"
• salary 0.0
• public String GetFirstName()
• return firstName
• public String GetLastName()
• return lastName

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Client Program

• A Program that Uses a Class Is a Client of that
  Class
• Class Objects are Declared and Instantiated Using
  the new keyword.
• new ClassName(parameters) Calls Constructor for
  Class
• Class Public Methods Called Using Dot (e.g.,
  variable.GetFirstName())
• variable is the invoking object

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• class useEmployee //useEmployee.java
• public static void main(String args)
• Employee emp1 new Employee()
• System.out.println("Name is"
  emp1.GetFirstName() " " emp1.GetLastName())
  

firstName
emp1
NoFirstName
lastName
NoLastName
salary
0.0
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Mutator Methods

• Class Methods Used to Modify a Class Object are
  Called Mutator Methods
• Allows Restricted Manipulation of Class Object
  Data

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• public boolean SetSalary(double passedSalary)
• if (passedSalary lt MAXSALARY)
• salary passedSalary
• return true
• else
• return false

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• class useEmployee
• public static void main(String args)
• Employee emp1 new Employee()
• System.out.println("Name is"
  emp1.GetFirstName() " " emp1.GetLastName())
• if (emp1.SetSalary(55000))
• System.out.println("Salary set to 55000")
• else
• System.out.println("Salary not set")

21
Static Variables and Methods

• static means in class methods and variables
• static variable one per class (not one per
  object)
• static method no invoking object (invoke with
  className.method())
• Example Math class methods

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Static Variable Example

• public class MyClass
• private final int STARTID 1
• //the following are one per object
• private int IDNum -1
• //the following are one per class
• private static int nextIDNum STARTID
• public MyClass()
• IDNum nextIDNum
• nextIDNum

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Static Method Example

• public class MyClass
• private final int STARTID 1
• //the following are one per object
• private int IDNum -1
• //the following are one per class
• private static int nextIDNum STARTID
• public static int GetNextID()
• // Called by MyClass.GetNextID()
• return nextIDNum

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Other Class Methods

• boolean equals( objType comObj)
• compares invoking object with passed object
• Returns true if both are equal, false if not
• void display()
• Displays attributes
• String toString()
• Converts all attributes to String and returns
  String