Initializing Arrays char c Array 3 a b

Initializing Arrays char [] c. Array 3 = {'a', 'b', 'c'}; int [] i. Array = {1, 2, 3, 4}; double [] d. Array = {3. 4, 5. 67 e 4};

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

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 Class. Name. 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 Employee first. Name last. Name salary

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

class Employee // Employee. java { private String first. Name; private String last. Name; private double salary; public Employee() { first. Name = "No. First. Name"; last. Name = "No. Last. Name"; salary = 0. 0; } }

Accessor Methods • Public Methods for Getting Attributes of Class

class Employee { private String first. Name; private String last. Name; private double salary; public Employee() { first. Name = "No. First. Name"; last. Name = "No. Last. Name"; salary = 0. 0; } public String Get. First. Name() { return first. Name; } public String Get. Last. Name() { return last. Name; } public double Get. Salary() { 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 Class. Name(parameters) Calls Constructor for Class • Class Public Methods Called Using Dot (e. g. , variable. Get. First. Name(); )

class use. Employee //use. Employee. java { public static void main(String [ ] args) { Employee emp 1 = new Employee(); System. out. println("Name is" + emp 1. Get. First. Name() + " " + emp 1. Get. Last. Name()); } first. Name } emp 1 “No. First. Name” last. Name “No. Last. Name” salary 0. 0

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

public boolean Set. Salary(double passed. Salary) { if (salary <= MAXSALARY) { salary = passed. Salary; return true; } else { return false; } }

class use. Employee { public static void main(String [ ] args) { Employee emp 1 = new Employee(); System. out. println("Name is" + emp 1. Get. First. Name() + " " + emp 1. Get. Last. Name()); if (emp 1. Set. Salary(55000)) { System. out. println("Salary set to 55000"); } else { System. out. println("Salary not set"); } } }