Image Processing

Classes, Types and ObjectsClasses, Types and Objects

Data StructuresData Structures

Chapter 1Chapter 1

Prof. Vidya Manian

Dept. of Electrical and Comptuer Engineering

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Java Programming Basics

ECE, UPRM

Overview

•Objects, classes

•expressions

•Control flow

•Arrays

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Objects

•Objects –store data and provide methods foraccessing and modifying data

•An object is an instance (member) of a class

•Class – specifies type of objects, operationsthat it performs

•Data of objects are stored as instancevariables (fields) (of types e.g. integers,floating point numbers, Booleans)

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Operations

•Methods :constructors, procedures, andfunctions

•Example: class declaration

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•Counter class is public-other class can createand use a counter object

•Instance variable –count

•Constructor method initializes it to 0

•Accessor method, get Count

•Update methods, incrementCount,decrementCount

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Class modifiers

•Abstract-empty methods with abstractkeyword

•Final – cannot have subclasses

•Public – can be instantiated by anything thatimports the class

•Base types (primitve types (boolean, char,byte, short, int, long, float, double)

•Int x, x=14 or x=195

•Float, y=3.1415

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Example of base types

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•Comments: /** **/ or //

•‘new’ creates a new object and returnsreference to that object

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new operator

•A new object is dynamically allocated inmemory, initialized to default values ‘null’

•Constructor is called

•The new operator returns a reference (amemory address) to the newly created object

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Number classes

•Byten.byteValue()

•Shortn.shortValue()

•Integern.intValue()

•Longn.longValue()

•Floatn.floatValue()

•Doublen.doubleValue()

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String objects

•String is a sequence of characters that comesform some alphabet (set of possiblecharacters)

•P = “barney the bear”

•Length 15

•Concatenation

•String s = “kilo” + “meters”

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Object reference

•Reference variable is a pointer to some object

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Dot operator

•Can have many references to the same object

•Dot operator”.”-access methods and instancevariables associated with an object

•Examples of signatures (methods name withparameters)

•oven.cookDinner();

•oven.cookDinner(food);

•oven.cookDinner(food,seasoning);

•Note: Java doesn not allow 2 methods withthe same signature to return different types

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Instance Variables

•Instance variables must have a type (int, float,double) or a reference type : class such asString, an array

•A referrence variable v, points to object o, wecan access any of the instance variables fo othat the access rules allow

•Public instance variables are accessible byeveryone

•Dot operator can get and set the value of anyinstance variable (v.i)

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•gnome.name =“professor smith”;

•gnome.age=35;

•gnome –reference to a Gnome object, withpublic instance variables name and age

•Variable modifiers

•Public: anyone can access

•Protected: only methods of the same packageor of its subclasses can access protectedinstance variables

•Private: only methods of the same class canaccess it

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•Static: variables are used to store “global”information about a class

•Final: a final instance variable is one that mustbe assigned an initial value, and can never beassigned a new value after that(MAX_HEIGHT)

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•What are the base types ?

•What is variable gnomeBuddy ?

•What is variable name ?

•Note: Constant values associated with a classshould be declared to be both static and final

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Enum Types

•Take on values from a specified set of names

•Modifier enum name {value_name0,value_name1,….};

•Modifer – black, public, protected or private

•Name – any legal Java identifier

•public enum Day{MON,TUE,WERD,THU,FRI,SAT,SUN}

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•Output:

•Initially d is MON

•Then it is WED

•I say d and t are the same: true

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Methods

•Similar to functions and procedures

•Method has 2 parts: body and signature

modifiers type name(type0 parameter0, …typen-1 parametern-1) {

// method body…

}

•type is the return type of the method, name –name of the method

•When a method of a class is called, it isinvoked on a specific instance of the class andcan change the state of the object

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•Similar to instance variables, Methodmodifiers can be public, protected, private orabstract

•Note: All parameters are passed by value,changing the internal reference inside amethod will not change the reference thatwas passed in

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Constructors

•A constructor is a special kind of method thatis used to initialize newly created objects

•Note: name of constructor, name, must besame as the name of the class it constructs

•Return type not specified for constructor

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•Constructor definition and invocation

•Return statements are not allowed in aconstructor body

•A new instance of this class is created and itsconstructor is used to initialize its isntancevariables

•Must be called using new operator

•Fish myFish = new Fish(y, “Wally”);

•Classes that define Stand – alone Javaprogram has the main method

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•Java Aquarium //system looks for compiledversion of Aquarium class and invokes thespecial main method in that class

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Statement blocks and localvariables

•Two ways of declaring local variables

•type name;

•type name = initial_value;

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Expressions

•Expressions involve the use of literals,variables and operators

•Variables and constants are used expressionsto define new values/modify variables

•Literal: is any “constant” value

–Null object reference

–Boolean: true and false

–Integer: type int, (32-bit integer), long iteger: 176Lor -52l (64-bit integer)

–Floating point: default for floating point numbersis double, 3.14E2 or .19e10

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–Character, ‘a’, ‘?’ are character constants

–Special characters

–String literal: sequence of characters “have a niceday”

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Operators

•Assignment operator : variable=expression

•i = j = 25;

•Arithmetic operators: +, -, *, /, %

•Increment and decrement operators

–int i=8;

–int j=i++;

–int k=++i;

–int m=i--;

–int n = 9+i++;

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Logical operators

•< , <=, ==, !=, >=, >

•Boolean: ! Not

•&& conditional and, || conditional or

•Bitwise operators: ~ bitwise complement, &bitwise and, | bitwise or, ^ bitwise exclusiveor, <<, >>, >>>

•Operational assignment operators: variable op= expression

•Variable = variable op expression

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Arrays

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Declaring arrays

•Element_type[] array_name = {init_val_0,init_value_1,.., init_val_N-1}

•int[] primes = {2,3,5,7,11}

•element_type[] array_name;

•new element_type[length]

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Arrays are objects

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Cloning an array

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// Example 1 // --------- // First declare

//reference and then construct it.

int[] ExampleArray1;

ExampleArray1 = new int[24];

// Example 2 // --------- // This can be considered

//the short form for declaring and construction.int[] ExampleArray2 = new int[24];

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// Example 3 // --------- // Construct and assign

//an array using a single command.

String[] ExampleArray3 = { "Sun Solaris" , "HP-UX" , "Linux" , "MS Windows" , "Macintosh" };

int[] array = null;

int[] arr = new int[] {1,2,3};

int[][] twoDimArray = { {1,2,3}, {4,5,6}, {7,8,9} };

int[][] myArray = new int[5][];

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Testing 2D array

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class TestTwoDimArrays { // initialize # of rows

static int [][] myArray = new int[3][];

public static void main(String[] args) {

myArray[0] = new int[3]; // initialize # of cols

myArray[1] = new int[4]; // in each row

myArray[2] = new int[5];

for(int i=0; i<3; i++)

// fill and print the array

fillArray(i, i+3); System.out.println(); }

// end main()

private static void fillArray(int row, int col) {

for( int i=0; i<col; i++)

myArray[row][i] = i;

for( int i=0; i<col; i++)

System.out.print(myArray[row][i]);

System.out.println();

}

Exercises in group

•Suppose that we create an array A ofGameEntry objects, with integer scores field,we cloe A and store the result in an array B. Ifwe set A[4].score =550, what is the scorevalue of GameEntry object referenced byB[4]?

•Write a Java method that takes an array of intvalues and determines if all the numbers aredifferent from each other.

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