Java fundamentals

Java Language Fundamentals

Java Simplified / Session 2 / 1 of 28

Objectives
 Java Overview
 Interpret the Java Program
 Understand the basics of Java Language
 Identify the Data Types
 Understand arrays
 Identify the Operators
 Format output using Escape Sequence

Overview
 Java is an Object-Oriented Programming (OOP)
Language
 Can be considered as (((C++)--)++)
 Eliminate unnecessary complexities in C++ like
 Multiple Inheritance
 Pointer
 Better features as oppose to C++
 Platform independence
 Support for the internet
 Security

Features of Java
 Simple
 Object-oriented
 Compiled and interpreted
 Portable
 Distributed
 Secure

Programming Environment
 Command line
javac hello.java
java hello
 Integrated Development Environment (IDE)
Eclipse
NetBeanIDE

Java Development Kit (JDK)
 Contains the software and tools needed to
compile, debug and execute applets and
applications
 A set of command line tools
 Current release: Java 1.6.x
 Freely available at Sun’s official website
http://www.oracle.com/technetwork/java/javaee/do
wnloads/index.html

Java Simplified / Session 1 / 7 of 32

A Sample Java program

// This is a simple program called First.java
class First
{
public static void main (String [] args)
{
System.out.println ("My first program in Java ");
}
}

Compiling and executing

The java compiler creates a file called 'First.class'
that contains the byte codes
To actually run the program, a java interpreter called java
is required to execute the code.

Passing Command Line Arguments
class CommLineArg
{
public static void main (String [] pargs)
{
System.out.println("These are the arguments passed to
the main method.");
System.out.println(pargs [0]);
}
}

Passing Command Line Arguments
Output

Basics of the Java Language
Data types

Classes Variables

Java
Basics

Control
Operators
Structures

Keywords
abstract boolean break byte byvalue
case cast catch char class
const continue default do double
else extends false final finally
float for future generic goto
if implements import inner Instanceof
null operator outer package private
protected Public rest return short
static Super switch synchronized this
threadsafe Throw throws transient true
try Var void volatile while

Primitive Data types
Data type Size Range
byte 1 -128-127
short 2 -32768-32767
int 4 -2,147,483,648-2,147,483,647
long 8 -263-263-1
float 4
double 8
boolean 1 bit true, false
char 2 Single character

Variables
 Variables must be declared before using,
 Syntax
datatype identifier [=value][, identifier[=value]...];
 Three components of a declaration are:
 Data type
 Name
 Initial value to be assigned (optional)

Example
int numberOfStudents;
String name;
double x, y;
boolean isFinished;
char firstInitial, middleInitial, lastInitial;

Example
class DynVar
{
public static void main(String [] args)
{
double len = 5.0, wide = 7.0;
double num = Math.sqrt(len * len + wide * wide);
System.out.println("Value of num after dynamic initialization is " + num);
}
}

Output

Scope and Lifetime of Variables
 Variables can be declared inside a block.
 The block begins with an opening curly brace and
ends with a closing curly brace.
 A block defines a scope.
 A new scope is created every time a new block is
created.
 Scope specifies what objects are visible to other
parts of the program.
 It also determines the life of an object.

Example
class ScopeVar
{
{
int num = 10;
if ( num == 10)
{
// num is available in inner scope
int num1 = num * num;
System.out.println("Value of num and num1 are " + num + " " + num1);
}
//num1 = 10; ERROR ! num1 is not known
System.out.println("Value of num is " + num);
}
}
Output

Type Casting
 In type casting, a data type is converted into
another data type.
 Example
float c = 34.89675f;
int b = (int)c + 10;

Automatic type and Casting
 There are two type of data conversion: automatic type
conversion and casting.
 When one type of data is assigned to a variable of
another type then automatic type conversion takes
place provided it meets the conditions specified:
 The two types are compatible
 The destination type is larger than the source type.
 Casting is used for explicit type conversion. It loses
information above the magnitude of the value being
converted.

Type Promotion Rules
 All byte and short values are promoted to int
type.
 If one operand is long, the whole expression is
promoted to long.
 If one operand is float then the whole
expression is promoted to float.
 If one operand is double then the whole
expression is promoted to double.

Array Declarations
 Three ways to declare an array are:
datatype [] identifier;
int [] anArray;
anArray = new int[10];
datatype [] identifier = new datatype[size];
int [] anArray = new int[10];
datatype [] identifier = {value1,value2,….valueN};
int [] anArray = {100,200,300,400,500};

Example – One Dimensional Array
class ArrDemo
{
public static void main(String [] arg)
{
double nums[] = {10.1, 11.3, 12.5,13.7, 14.9};
System.out.println(" The value at location 3 is : " +
nums[3]);
}
}

Output

Example – Multi Dimensional Array
class MultiArrayDemo
{
public static void main ( String [] arg)
{
int multi[][] = new int [4][];
multi[0] = new int[1];
int num = 0;
for (int count = 0; count < 4; count++)
{
for (int ctr = 0; ctr < count+1; ctr++)
{
multi[count][ctr] = num;
num++;
}
}

Operators
 Arithmetic Operators
 Relational Operators
 Logical Operators
 Conditional Operators
 Assignment operators

Arithmetic Operators
 Operands of the arithmetic operators must be of
numeric type.
 Boolean operands cannot be used, but character
operands are allowed.
 These operators are used in mathematical
expressions.

Example
class ArithmeticOp {
public static void main ( String [] arg) {
int num = 5, num1 = 12, num2 = 20, result;
result = num + num1;
System.out.println("Sum of num and num1 is : (num + num1) " + result);
result = num % num1;
System.out.println("Modulus of num and num1 is : (num % num1) " + result);
result *= num2;
System.out.println("Product of result and num2 is : (result *= num2) " + result);
}
}

Relational Operators
 Relational operators test the relation between two
operands.
 The result of an expression in which relational
operators are used, is boolean (either true or false).
 Relational operators are used in control structures.

Example
class RelOp
{
{
float num = 10.0F;
double num1 = 10.0;
if (num == num1)
System.out.println ("num is equal to num1");
else
System.out.println ("num is not equal to num1");
}
} Output

Logical Operators
 Logical operators work with boolean operands.
 Some operators are
&
|
^
!

Conditional Operators
 The conditional operator is unique, because it is a ternary or
triadic operator that has three operands to the expression.
 It can replace certain types of if-then-else statements.
 The code below checks whether a commuter’s age is greater
than 65 and print the message.
CommuterCategory = (CommuterAge > 65)? “Senior Citizen” : “Regular”;

Assignment Operators
 The assignment operator is a single equal sign, =,
and assigns a value to a variable.
 Assigning values to more than one variable can be
done at a time.
 In other words, it allows us to create a chain of
assignments.

Operator Precedence
 Parentheses: ( ) and [ ]
 Unary Operators: +, -, ++, --, ~, !
 Arithmetic and Shift operators: *, /, %, +, -, >>, <<
 Relational Operators: >, >=, <, <=, ==, !=
 Logical and Bitwise Operators: &, ^, |, &&, ||,
 Conditional and Assignment Operators:
?=, =, *=, /=, +=, -=
 Parentheses are used to change the order in which an
expression is evaluated. Any part of an expression
enclosed in parentheses is evaluated first.

Classes in Java
 Class declaration Syntax

class Classname
{
var_datatype variablename;
:

met_datatype methodname(parameter_list)
:
}

Formatting output with Escape Sequences
 Whenever an output is to be displayed on the
screen, it needs to be formatted.
 The formatting can be done with the help of escape
sequences that Java provides.
System.out.println (“Happy tBirthday”);
 Output: Happy Birthday

Control Flow
 All application development environments provide a
decision making process called control flow
statements that direct the application execution.
 Flow control enables a developer to create an
application that can examine the existing
conditions, and decide a suitable course of action.
 Loops or iteration are an important programming
construct that can be used to repeatedly execute a set
of actions.
 Jump statements allow the program to execute in a
non-linear fashion.

Control Flow Structures in Java
 Decision-making
 if-else statement
 switch-case statement
 Loops
 while loop
 do-while loop
 for loop

if-else statement
 The if-else statement tests the result of a condition, and
performs appropriate actions based on the result.
 It can be used to route program execution through two different
paths.
 The format of an if-else statement is very simple and is given
below:
if (condition)
{
action1;
}
else
{
action2;
}

Example
class CheckNum
{
{
int num = 10;
if (num % 2 == 0)
System.out.println(num + " is an even number");
else
System.out.println(num + " is an odd number");
}
}

switch – case statement
 The switch – case statement can be used in place of
if-else-if statement.
 It is used in situations where the expression being
evaluated results in multiple values.
 The use of the switch-case statement leads to
simpler code, and better performance.

Example
class SwitchDemo
{
public static void main(String[] args)
{
int day = 4;
String str; case 5:
switch (day) str = "Friday";
{ case 0:
break;
case 6: str = "Sunday";
str = "Saturday";
break;
case 1:
break;
default: str = "Monday";
str = "Invalid day";
break;
case 2:
}
System.out.println(str);
str = "Tuesday";
Output
} break;
} case 3:
str = "Wednesday";
break;
case 4:
str = "Thursday";
break;

while Loop
 while loops are used for situations when a loop has to
be executed as long as certain condition is True.
 The number of times a loop is to be executed is not pre-
determined, but depends on the condition.
 The syntax is:
while (condition)
{
action statements;
.
.
}

Example
class FactDemo
{
{
int num = 5, fact = 1;
while (num >= 1)
{
fact *= num;
num--;
}
System.out.println("The factorial of 5 is : " + fact);
} Output
}

do – while Loop
 The do-while loop executes certain statements till the
specified condition is True.
 These loops are similar to the while loops, except that a
do-while loop executes at least once, even if the
specified condition is False. The syntax is:
do
{
action statements;
.
.
} while (condition);

Example
class DoWhileDemo
{
{
int count = 1, sum = 0;
do
{
sum += count;
count++;
}while (count <= 100);
System.out.println("The sum of first 100 numbers
is : " + sum);
}
}
Output
The sum of first 100 numbers is : 5050

for Loop
Syntax:
for (initialization statements; condition; increment / decrement
statements)
{
action statements;
.
.
}

Example
class ForDemo
{
public static void main(String [] args) {
int count = 1, sum = 0;
for (count = 1; count <= 10; count += 2) {
sum += count;
}
System.out.println("The sum of first 5 odd numbers is : " + sum);
}
}

Output
The sum of first 5 odd numbers is : 25

Jump Statements
 Three jump statements are:
 break
 continue
 return
 The three uses of break statements are:
 It terminates a statement sequence in a switch
statement.
 It can be used to exit a loop.
 It is another form of goto.

Example
class BrDemoAppl
{
{
for (int count = 1; count <= 100; count++)
Output {
The value if of num 10) : 1
(count == is
break;
The value of num is : 2
The value of num is : 3 value of num is : " + count);
System.out.println("The
}
System.out.println("The loop is over");
}
The} value of num is : 6
The loop is over

Summary
 A Java program consists of a set of classes. A program may contain
comments. The compiler ignores this commented lines.
 The Java program must have a main() method from where it begins
its execution.
 Classes define a template for units that store data and code related to
an entity.
 Variables defined in a class are called the instance variables.
 There are two types of casting:widening and narrowing casting.
 Variables are basic unit of storage.
 Each variable has a scope and lifetime.
 Arrays are used to store several items of same data type in consecutive
memory locations.

Summary Contd…
 Java provides different types of operators. They include:
 Arithmetic
 Bitwise
 Relational
 Logical
 Conditional
 Assignment
 Java supports the following programming constructs:
 if-else
 switch
 for
 while
 do-while
 The three jump statements-break,continue and return helps to
transfer control to another part of the program.

Java fundamentals

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