Fundamentals 2

1. Fundamentals 2

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

3. 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.

4. 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, _.

5. 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.

6. Java built-in Data Types

7. Primitive Data Types

8. 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.

9. 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.

10. 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;

11. 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; • Boolean declaration: • with initial value: • boolean flag=false; • boolean valid=true; • without initial value: • boolean flag;

12. 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

13. 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 Dr. S. GANNOUNI & Dr. A. TOUIR

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

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

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

17. Example Exampleof 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. Dr. S. GANNOUNI & Dr. A. TOUIR

18. Modulus • Generates the remainder when you divide two integer values. • 5%3 gives 2 5%4 gives 1 • 5%5 gives0 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! Dr. S. GANNOUNI & Dr. A. TOUIR

19. 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 Dr. S. GANNOUNI & Dr. A. TOUIR

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

21. 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; Dr. S. GANNOUNI & Dr. A. TOUIR

22. Relational Operators • Relational operators compare two values • They Produce a boolean value (true or false) depending on the relationship Dr. S. GANNOUNI & Dr. A. TOUIR

23. 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 Dr. S. GANNOUNI & Dr. A. TOUIR

24. Logical Operators Symbol Name && AND || OR ! NOT Dr. S. GANNOUNI & Dr. A. TOUIR

25. 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 Dr. S. GANNOUNI & Dr. A. TOUIR

26. Operators Precedence Dr. S. GANNOUNI & Dr. A. TOUIR

27. 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. Dr. S. GANNOUNI & Dr. A. TOUIR

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“ ); The println Method • We use println instead of print to skip a line. x = 123 x + x = 246 THE END Dr. S. GANNOUNI & Dr. A. TOUIR

29. 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 aScanner • 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(); Dr. S. GANNOUNI & Dr. A. TOUIR

30. Example import java.util.Scanner; publicclass TestInput { publicstaticvoid 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); } } Dr. S. GANNOUNI & Dr. A. TOUIR

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

32. 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(); Dr. S. GANNOUNI & Dr. A. TOUIR