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Basic Concepts

Mehdi Einali

Advanced Programming in Java

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agendaReviewUser input

ScannerStrong type checkingOther flow-control structures

switchbreak & continue

StringsArrays

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reviewVariables

Primitive data typesOperatorsMethods

Parameter passingCall by value

ConditionsIf, else, else if

Loopswhiledo-whilefor

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VariablesVariables defined and initialized

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Variables2 types of variables

Class variables(Fields)Local variables

Method VariableMethod parameterBlock Variable

There is no global variablesJava use static binding for variables

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VariablesA variable always refers to its nearest enclosing binding.(Scoping)

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User InputPrint on console

System.out.printlnHow to read from console?ScannerExample:

Scanner scanner = new Scanner(System.in);int n = scanner.nextInt();double d = scanner.nextDouble();

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ExampleScanner scanner = new Scanner(System.in);

int a = scanner.nextInt();int b = scanner.nextInt();long pow = power(a,b);System.out.println(pow);

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Type CheckingJava has a strong type-checking mechanismSome assignment is not permitted

int intVal = 2;long longVal =12;

intVal = longVal;Syntax ErrorlongVal = intVal;OKintVal = (int)longVal; OK (Type Casting)

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Direct Type castThe arrows are transitiveAll other conversions need an explicit castboolean is not convertiblechar is a special type

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Type Conversion Grid

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Type ConversionN : the conversion cannot be performedY : the conversion is performed automatically and implicitly by JavaC : the conversion is a narrowing conversion and requires an explicit castY* : the conversion is an automatic widening conversion, but that some of the least significant digits of the value may be lost by the conversion

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Examplei = 123456789; //a big integerf = i; //f stores and approximation of iSystem.out.println(f);//output : 1.23456792E8i = (int) f;System.out.println(i); //output : 123456792

floating-point types are approximations of numbers They cannot always hold as many significant digits as the integer types

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ComparisonCompare doublesUsing == with float or double is an anti-patternAn infinite loop:

for (float f = 10f; f != 0; f -= 0.1) {System.out.println(f);

}

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Numeric AssignmentsNumeric Suffix

Double d = 123.54d;Float f = 123f;Long l = 123123 l; byte b = 127;//Nothing

Assignment OverflowLarge long to int

Lower bits are usedNo runtime error

Large double to integerBrings a max int

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Operators and castDivision (“/”) operates differently on integers and on doubles!

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Flow controls

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Structured programmingSequence

SelectionIf-elseswitch-case

Iterationforwhiledo-while

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BlockSometimes a group of statements needed tobe executed in all ornothing manner

It is same as single statement and can

be replaced with a method

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Block Variable

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If-else

Braces is optional for single statementRemember: place braces for clarify for indentation

else will bind to last if

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Short cut Boolean evaluation

&& vs & , || vs |

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Loop-1Constructs

InitializeStepTermination condition

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Loop-2

Watch out infinite loop

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Switch statementswitch (i) {case 1:

System.out.println("1");break;

case 2:System.out.println("2");break;

default:System.out.println("default");

}

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BreakJump out of loop block

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ContinueStops the execution of the body of the loop and continues from the beginning of the loop

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Nested loopouter: for (int i = 0; i < 10; i++){inner: for (int j = 0; j < 10; j++) {

if (j == 2){break outer;

} else {System.out.println(i);System.out.println(j);continue inner;

} }}

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Switch without break01234456789

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CommentsComments are ignored by compilerOne-line comment

//nextInt = scanner.nextInt();

Multiple-line comment/*nextInt = scanner.nextInt();for(int i=0;i<nextInt;i++){

System.out.println(i);} */

Javadoc comments/** * ... text ... */

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String

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StringA sequence of charactersCharacter:

char ch = ‘a’;char ch = ‘1’;char ch = ‘#’;

Strings:String st = “Ali”;String st = “123”;String st = “1”;String st = “”;

String is not a primitive type

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StringString in C and C++

char* and char[]\0 at the end of String

Some functionsstrlen, strcpy, …

String in java is a classString in java is not equal to char[]Constant strings

“salam!”“Hellow World!”

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String and other typesString input = "Nader and Simin, A Separation";char ch = input.charAt(0);int i = input.indexOf("Nader");int j = input.lastIndexOf("Simin");String newS = input.replace("Separation", "Reconciliation");String sth = newS + ch + i + j;System.out.println(sth);

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String methodscharAtconcat plus (+) operatorcontainsstartsWithendsWithindesxOf first index of sthlastIndexOfreplacesubstringlengthsplit

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Immutable StringString in java is an immutable classAfter creating a string, you can not change itIf you want to change it, you should create a new stringThere is no such methods for strings:

setCharAt(int)setValue(String)

Methods like replace and replaceAll, do not change the value

They return a new String

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exampleWhat is the output of this code?

String str = "Gholi";str.replaceAll("li", "lam");System.out.println(str);

String str = "Gholi";String replaced =

str.replaceAll("li", "lam");

System.out.println(replaced);

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Data HierarchyBitByteCharacterWord

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Java CharactersSome characters are special charactersSpecial characters are shown using backslashExamples:

New line: \nTab : \tDouble-quote : \”Single-quote : \’Backslash : \\

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Arrays

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ArrayCollections of related data itemsrelated data items of the same typeArrays are fixed-length entities they remain the same length once they are createdAn array is a group of variables

called elementscontaining values that all have the same typeThe position number of the element is it’s indexArray elements are sequentially located in memory

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samplesCreate an array of 10 integer elements

int[] array = new int[10]; int array[] = new

int[10];//equalCreate an array of n characters

char[] characters = new char[n];Change value of 5’th element

array[5] = 12;Retrieving value of n’th element

char ch = array[n];

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Array Creation Shortcutchar[] array = new char[3];array[0] = 'a';array[1] = 's';array[2] = 't';The above code can be rewritten as:char[] array = {'a','s','t'};Other examples:int[] numbers = {1,2,3,5,9,123};boolean[] b = {true, true, false, true};

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Multidimensional Arraysint[][] matrix = new int[3][4];matrix[2][3] = 2;System.out.println(matrix[2][1]);

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Unbalanced Multidimensional Array

int[][] matrix = new int[3][];matrix[0] = new int[2];matrix[1] = new int [5];matrix[2] = new int [4];matrix[2][3] = 2;System.out.println(matrix[2][1]);matrix[0][3] = 2;//Runtime Error

ArrayIndexOutOfBoundsException

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Quiz (5min)

a)-ab@db)-ab@d@c)-a@d@d)-abd@e)exception

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end