FUNDAMENTALS 2 CHAPTER 2
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FUNDAMENTALS 2CHAPTER 2
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
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.
EXAMPLEExample 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.
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!
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
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
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
|| T F
T T T
F T F
Symbol Name
&& AND
|| OR
! NOT
&& T F
T T F
F F F
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? "); // promptint age = console.nextInt();System.out.println("You'll be 40 in " + (40 - age) + " years.");
prompt: A message telling the user what input to type.
Method Description
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
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();
EXAMPLE SCANNER USAGEimport 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? 14
14... 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: 8 6 13
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
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COMMONLY USED ESCAPE SEQUENCES
PARSING
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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.
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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") = 6723Integer.parseInt("-823") = -823
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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") = 34.56Float.parseFloat("-542.97") = -542.97
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") = 345.78Double.parseDouble("-782.873") = -782.873
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