Fundamentals 2

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

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.

State My be changed  variable Cannot be changed  constant 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, _.

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.

Java built-in Data Types

Primitive Data Types Type Size (bits) Range Description boolean true, false Stores a value that is either true or false. char 16 0 to 65535 Stores a single 16-bit Unicode character. byte 8 -128 to +127 Stores an integer. short -32768 to +32767 int 32 bits -2,147,483,648 to +2,147,483,647 long 64 bits -9,223,372,036,854,775,808 to +9,223,372,036,854,775,807 float accurate to 8 significant digits Stores a single-precision floating point number. double accurate to 16 significant digits Stores a double-precision

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.

Constant Declaration final dataType constIdentifier = literal | expression; final int MAX = 1024; final int MIN = 128; final int AVG = (MAX + MIN) / 2; 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;

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

Exercises Student name 1course course*name 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

Dr. S. GANNOUNI & Dr. A. TOUIR Operators Operators are special symbols used for: mathematical functions assignment statements logical comparisons Examples of operators: 3 + 5 // uses + operator 14 + 5 – 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

Dr. S. GANNOUNI & Dr. A. TOUIR 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

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

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

Dr. S. GANNOUNI & Dr. A. TOUIR Example Example of division issues: 10 / 3 gives 3 10.0 / 3 gives 3.33333 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. Introduction to OOP Dr. S. GANNOUNI & Dr. A. TOUIR

Dr. S. GANNOUNI & Dr. A. TOUIR Modulus Generates the remainder when you divide two integer values. 5%3 gives 2 5%4 gives 1 5%5 gives 0 5%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! Introduction to OOP Dr. S. GANNOUNI & Dr. A. TOUIR

Example: Sum of two integer 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 Introduction to OOP Dr. S. GANNOUNI & Dr. A. TOUIR

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

Increment/Decrement Operators 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; Introduction to OOP Dr. S. GANNOUNI & Dr. A. TOUIR

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

Dr. S. GANNOUNI & Dr. A. TOUIR 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

Dr. S. GANNOUNI & Dr. A. TOUIR Logical Operators Symbol Name && AND || OR ! NOT && T F || T F Introduction to OOP Dr. S. GANNOUNI & Dr. A. TOUIR

Dr. S. GANNOUNI & Dr. A. TOUIR 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

Dr. S. GANNOUNI & Dr. A. TOUIR 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

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

Dr. S. GANNOUNI & Dr. A. TOUIR The println Method We use println instead of print to skip a line. 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 Introduction to OOP Dr. S. GANNOUNI & Dr. A. TOUIR

Dr. S. GANNOUNI & Dr. A. TOUIR 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 OOP Dr. S. GANNOUNI & Dr. A. TOUIR

Dr. S. GANNOUNI & Dr. A. TOUIR Example 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); } Introduction to OOP Dr. S. GANNOUNI & Dr. A. TOUIR

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

Common Scanner Methods Method Example 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 OOP Dr. S. GANNOUNI & Dr. A. TOUIR