FUNDAMENTALS 2 CHAPTER 2

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

GROUPS OF OPERATORS  There are 5 different groups of operators:  Arithmetic Operators  Assignment Operator  Increment / Decrement Operators  Relational Operators  Logical Operators

JAVA ARITHMETIC OPERATORS Addition+ Subtraction – Multiplication  Division / Remainder (modulus )% Assignment Operator =

ARITHMETIC OPERATORS  The following table summarizes the arithmetic operators available in Java.

EXAMPLE 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  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 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 Java allows combining arithmetic and assignment operators into a single operator: Addition/assignment += Subtraction/assignment -= Multiplication/assignment  = Division/assignment /= Remainder/assignment %=

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;

RELATIONAL OPERATORS 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  Relational operators compare two values  They Produce a boolean value (true or false) depending on the relationship

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

LOGICAL OPERATORS || TF TTT FTF Symbol Name && AND || OR ! NOT && TF TTF FFF

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

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=, +=, -=, *=, /=, %=

INPUT & OUTPUT

INPUT AND SYSTEM.IN  System.out  An object with methods named println and print  System.in  not intended to be used directly  We use a second object, from a class Scanner, to help us.  Constructing a Scanner object to read console input: Scanner name = new Scanner(System.in);  Example: Scanner console = new Scanner(System.in);

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.

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

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();

JAVA CLASS LIBRARIES, IMPORT  Java class libraries: Classes included with Java's JDK.  organized into groups named packages  To use a package, put an import declaration in your program.  Syntax: // put this at the very top of your program import packageName.*;  Scanner is in a package named java.util import java.util.*; import java.util.Scanner;  To use Scanner, you must place the above line at the top of your program (before the public class header).

SCANNER METHODS Each method waits until the user presses Enter.  The value typed is returned. System.out.print("How old are you? "); // prompt int age = console.nextInt(); System.out.println("You'll be 40 in " + (40 - age) + " years.");  prompt: A message telling the user what input to type. MethodDescription nextInt() reads a token of user input as an int nextDouble() reads a token of user input as a double next() reads a token of user input as a String nextLine() reads a line of user input as a String

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();

EXAMPLE SCANNER USAGE import java.util.*; // so that I can use Scanner public class ReadSomeInput { public static void main(String[] args) { Scanner console = new Scanner(System.in); System.out.print("How old are you? "); int age = console.nextInt(); System.out.println(age + "... That's quite old!"); }  Output (user input underlined): How old are you? That's quite old!

ANOTHER SCANNER EXAMPLE import java.util.*; // so that I can use Scanner public class ScannerSum { public static void main(String[] args) { Scanner console = new Scanner(System.in); System.out.print("Please type three numbers: "); int num1 = console.nextInt(); int num2 = console.nextInt(); int num3 = console.nextInt(); int sum = num1 + num2 + num3; System.out.println("The sum is " + sum); }  Output (user input underlined): Please type three numbers: The sum is 27  The Scanner can read multiple values from one line.

INPUT TOKENS  token: A unit of user input, as read by the Scanner.  Tokens are separated by whitespace (spaces, tabs, newlines).  How many tokens appear on the following line of input? 23 John Smith 42.0 "Hello world" $2.50 " 19"  When a token is not the type you ask for, it crashes. System.out.print("What is your age? "); int age = console.nextInt(); Output: What is your age? Timmy java.util.InputMismatchException at java.util.Scanner.next(Unknown Source) at java.util.Scanner.nextInt(Unknown Source)...

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); }

OUTPUT enter the length 2 Enter the Width 3 the length is 2 the width is 3 the area is 6

29 COMMONLY USED ESCAPE SEQUENCES

PARSING

31 PARSING NUMERIC STRINGS  Integer, Float, and Double are classes designed to convert a numeric string into a number.  These classes are called wrapper classes.  parseInt is a method of the class Integer, which converts a numeric integer string into a value of the type int.  parseFloat is a method of the class Float and is used to convert a numeric decimal string into an equivalent value of the type float.  parseDouble is a method of the class Double, which is used to convert a numeric decimal string into an equivalent value of the type double.

32 PARSING NUMERIC STRINGS  A string consisting of only integers or decimal numbers is called a numeric string.  To convert a string consisting of an integer to a value of the type int, we use the following expression: Integer.parseInt(strExpression) Example: Integer.parseInt("6723") = 6723 Integer.parseInt("-823") = -823

33 PARSING NUMERIC STRINGS  To convert a string consisting of a decimal number to a value of the type float, we use the following expression: Float.parseFloat(strExpression) Example: Float.parseFloat("34.56") = Float.parseFloat(" ") =  To convert a string consisting of a decimal number to a value of the type double, we use the following expression: Double.parseDouble(strExpression) Example: Double.parseDouble("345.78") = Double.parseDouble(" ") =