Fundamentals 2 1

Programs and Data Most programs require the temporary storage of data. The data to be processed is stored in a temporary storage in the computer's memory: space memory. A space memory has three characteristics Identifier Data Type State 2

Identifier is a sequence of characters that denotes the name of the space memory to be used. This name is unique within a program. Identifier Rules It cannot begin with a digit (0 – 9). It may contain the letters a to z, A to Z, the digits 0 to 9, and the underscore symbol, _. No spaces or punctuation, except the underscore symbol, _, are allowed. Identifiers in Java are case-sensitive. Thus, the identifiers myNumber and mynumber, are seen as two different identifiers by the compiler. 3

State My be changed  variable All lowercase. Capitalizing the first letter of each word in a multiword identifier, except for the first word. Cannot be changed  constant All uppercase, separating words within a multiword identifier with the underscore symbol, _. 4

Data Type The data type defines what kinds of values a space memory is allowed to store. All values stored in the same space memory should be of the same data type. All constants and variables used in a Java program must be defined prior to their use in the program. 5

Java built-in Data Types 6

Primitive Data Types 7 Type Size (bits) RangeDescription booleantrue, falseStores a value that is either true or false. char160 to 65535Stores a single 16-bit Unicode character. byte8-128 to +127Stores an integer. short to Stores an integer. int32 bits-2,147,483,648 to +2,147,483,647 Stores an integer. long64 bits-9,223,372,036,854,775,808 to +9,223,372,036,854,775,807 Stores an integer. float32 bitsaccurate to 8 significant digitsStores a single-precision floating point number. double64 bitsaccurate to 16 significant digitsStores a double-precision floating point number.

Variable/Constant Declaration When the declaration is made, memory space is allocated to store the values of the declared variable or constant. The declaration of a variable means allocating a space memory which state (value) may change. The declaration of a constant means allocating a space memory which state (value) cannot change. 8

Constant Declaration final dataType constIdentifier = literal | expression; final int MAX = 1024; final int MIN = 128; final int AVG = (MAX + MIN) / 2; 9 These are called literals. This is called expression.

Variable Declaration A variable may be declared: – With initial value. – Without initial value. Variable declaration with initial value; dataType variableIdentifier = literal | expression; double avg = 0.0; int i = 1; int x =5, y = 7, z = (x+y)*3; Variable declaration without initial value; dataType variableIdentifier; double avg; int i; 10

More declaration examples String declaration – with initial value: String word="Apple"; – without initial value: String word; char declaration – with initial value: char symbol ='*'; – without initial value: char symbol; 11 Boolean declaration: – with initial value: boolean flag=false; boolean valid=true; – without initial value: boolean flag;

Exercises A-Declare a variable of double type with initial value=0.0; B- Declare a constant of String type with initial value=“Good” C- Declare a variable of type string with initial value equals to the value of constant in B. D-Is the following names are valid, why? – Student name – 1course – course*name 12

Operators Operators are special symbols used for: – mathematical functions – assignment statements – logical comparisons Examples of operators: – // uses + operator – – 4 * (5 – 3) // uses +, -, * operators Expressions: can be combinations of variables and operators that result in a value Introduction to OOP Dr. S. GANNOUNI & Dr. A. TOUIR Page 13

Groups of Operators There are 5 different groups of operators: – Arithmetic Operators – Assignment Operator – Increment / Decrement Operators – Relational Operators – Logical Operators Introduction to OOP Dr. S. GANNOUNI & Dr. A. TOUIR Page 14

Java Arithmetic Operators Introduction to OOP Dr. S. GANNOUNI & Dr. A. TOUIR Page 15 Addition+ Subtraction– Multiplication  Division/ Remainder (modulus )% Assignment Operator =

Arithmetic Operators The following table summarizes the arithmetic operators available in Java. Introduction to OOP Dr. S. GANNOUNI & Dr. A. TOUIR Page 16 This is an integer division where the fractional part is truncated.

Example Introduction to OOP Dr. S. GANNOUNI & Dr. A. TOUIR Page 17 Example of division issues : 10 / 3 gives / 3 gives As we can see, if we divide two integers we get an integer result. if one or both operands is a floating-point value we get a floating-point result.

Modulus Introduction to OOP Dr. S. GANNOUNI & Dr. A. TOUIR Page 18  Generates the remainder when you divide two integer values. 5%3 gives 25%4 gives 1 5%5 gives 05%10 gives 5  Modulus operator is most commonly used with integer operands. If we attempt to use the modulus operator on floating-point values we will garbage!

Example: Sum of two integer Introduction to OOP Dr. S. GANNOUNI & Dr. A. TOUIR Page 19 public class Sum { // main method public static void main( String args[] ){ int a, b, sum; a = 20; b = 10; sum = a + b; System.out.println(a + ” + ” + b + “ = “ + sum); } // end main } // end class Sum

Arithmetic/Assignment Operators Introduction to OOP Dr. S. GANNOUNI & Dr. A. TOUIR Page 20 Java allows combining arithmetic and assignment operators into a single operator: Addition/assignment+= Subtraction/assignment  = Multiplication/assignment  = Division/assignment/= Remainder/assignment %=

Increment/Decrement Operators Introduction to OOP Dr. S. GANNOUNI & Dr. A. TOUIR Page 21 Only use ++ or   when a variable is being incremented/decremented as a statement by itself. x++; is equivalent to x = x+1; x--; is equivalent to x = x-1;

Relational Operators Relational operators compare two values They Produce a boolean value (true or false) depending on the relationship OperationIs true when a >ba is greater than b a >=ba is greater than or equal to b a ==ba is equal to b a !=ba is not equal to b a <=ba is less than or equal to b a <ba is less than b Introduction to OOP Dr. S. GANNOUNI & Dr. A. TOUIR Page 22

Example int x = 3; int y = 5; boolean result; result = (x > y); now result is assigned the value false because 3 is not greater than 5 Introduction to OOP Dr. S. GANNOUNI & Dr. A. TOUIR Page 23

Logical Operators Symbol Name && AND || OR ! NOT || TF TTT FTF && TF TTF FFF Introduction to OOP Dr. S. GANNOUNI & Dr. A. TOUIR Page 24

Example boolean x = true; boolean y = false; boolean result; result = (x && y); result is assigned the value false result = ((x || y) && x); (x || y) evaluates to true (true && x) evaluates to true result is then assigned the value true Introduction to OOP Dr. S. GANNOUNI & Dr. A. TOUIR Page 25

Operators Precedence Parentheses(), inside-out Increment/decrement++, --, from left to right Multiplicative*, /, %, from left to right Additive+, -, from left to right Relational, =, from left to right Equality==, !=, from left to right Logical AND&& Logical OR|| Assignment=, +=, -=, *=, /=, %= Introduction to OOP Dr. S. GANNOUNI & Dr. A. TOUIR Page 26

Standard Output Window Using System.out, we can output multiple lines of text to the standard output window. Introduction to OOPDr. S. GANNOUNI & Dr. A. TOUIRPage 27 The exact style of standard output window depends on the Java tool you use.

The println Method We use println instead of print to skip a line. Introduction to OOPDr. S. GANNOUNI & Dr. A. TOUIRPage 28 int x = 123, y = x + x; System.out.print( " x = “ ); System.out.println( x ); System.out.print( " x + x = “ ); System.out.println( y ); System.out.println( " THE END“ ); x = 123 x + x = 246 THE END

Standard Input To input primitive data values, we use the Scanner class. 4 steps are needed to be able to use input primitive: – Step 1: import the Scanner class: import Java.util.Scanner; – Step 2 : declaring a reference variable of a Scanner Scanner read ; //we named the object read – Step 3: creating an instance of the Scanner read = new Scanner (System.in); – Step 4: use specific methods to enter data int x = read.nextInt(); Introduction to OOPDr. S. GANNOUNI & Dr. A. TOUIRPage 29

Example Introduction to OOPDr. S. GANNOUNI & Dr. A. TOUIRPage 30 import java.util.Scanner; public class TestInput { public static void main(String[] args) { Scanner input ; int area,length, width; input = new Scanner (System.in); // creating an instance System.out.println("enter the length "); length = input.nextInt(); //reading the length from the keyboard System.out.println("Enter the Width "); width = input.nextInt(); //reading the width from the keyboard area = length * width ; System.out.println("the length is "+ length); System.out.println("the width is "+ width); System.out.println("the area is "+ area); }

Output enter the length 2 Enter the Width 3 the length is 2 the width is 3 the area is 6 Introduction to OOPDr. S. GANNOUNI & Dr. A. TOUIRPage 31

Common Scanner Methods MethodExample Scanner input = new Scanner (System.in); nextByte( )byte b = input.nextByte( ); nextDouble( )double d = input.nextDouble( ); nextFloat( )float f = input.nextFloat( ); nextInt( )int i = input.nextInt( ); nextLong( )long l = input.nextLong( ); nextShort( )short s = input.nextShort( ); next() String str = input.next(); Introduction to OOPDr. S. GANNOUNI & Dr. A. TOUIRPage 32