Announcements Final Exam:TBD

public static void main(String [] args) { final int ASIZE = 5; int [] intArray= new int[ASIZE]; for(int i = 0; i < ASIZE; i++) intArray[i] = i; System.out.println( intArray[0]); changeZero(intArray); System.out.println( intArray[0]); } static void changeZero(int [] passedArray) { passedArray[0] = 1000; }

Initializing Arrays char [] cArray3 = {'a', 'b', 'c'}; int [] iArray = {1, 2, 3, 4}; double [] dArray = {3.4, 5.67e4};

Two Dimensional Arrays char [][] cArray = new char[10][20]; int [][] iArray = new int[100][50]; cArray[0][0] = ‘a’; cArray[0][1] = ‘b’; cArray[9][19] = ‘x’; iArray[0][0] = 99; iArray[1][5] = 135; iArray[99][49] = 0;

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

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

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

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

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)

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)

Example Class firstName lastName salary Class Employee

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

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; }

Accessor Methods Public Methods for Getting Attributes of Class

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; } public double GetSalary() { return salary; }

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

class useEmployee //useEmployee.java { public static void main(String [ ] args) { Employee emp1 = new Employee(); System.out.println("Name is" + emp1.GetFirstName() + " " + emp1.GetLastName()); } firstName lastName salary emp1 0.0 “NoFirstName” “NoLastName”

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

public boolean SetSalary(double passedSalary) { if (passedSalary <= MAXSALARY) { salary = passedSalary; return true; } else { return false; }

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"); }

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

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++; }

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; }

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