Session 2Session 2

Java Language Fundamentals

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ReviewReview

Java was introduced by Sun Microsystems in 1995. Java is a programming language popularly used to build programs that can

work on the Net. Its primary features are: it is object-oriented and a cross platform language. Swing, Drag and Drop, Java 2D API, Java Sound and RMI are some of the

features added to the existing version of Java. A Java applet is designed to work in a pre-defined “sandbox” only. This

makes it safe to be used on the Internet. Java bytecodes are machine language instructions understood by the Java

Virtual Machine and usually generated as a result of compiling Java language source code.

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Review Contd…Review Contd…

Java programs can be divided into following categories-applets, applications, GUI applications, servlets and database applications.

Java visual development tools help the programmer to develop Java applications and applets more quickly and efficiently.

The JDK contains the software and tools needed to compile, debug and execute applets and applications written in the Java language. It’s basically a set of command-line tools.

Enhancement in Swing, AWT, a new I/O class and so on has been added in the latest version of Java 1.4.2.

The future will use a lot of Java related programs for consumer gadgets with embedded technologies.

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ObjectivesObjectives

Interpret the Java ProgramUnderstand the basics of Java Language Identify the Data TypesUnderstand arrays Identify the OperatorsFormat output using Escape Sequence

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A Sample Java A Sample Java programprogram

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

}}

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Analyzing the Java Analyzing the Java Program Program

The symbol // stands for commented line. When longer comments are needed, mark each line with a //.

◦ Or use the /* and */ comment delimiters -> block off a longer comment

The line class First declares a new class called First. public static void main (String [] args)

◦ This is the main method from where the program begins its execution.

System.out.println (“My first program in java”);◦ object.method(parameters)

◦ This line displays the string My first program in java on the screen.

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Phase 1: Creating a Phase 1: Creating a ProgramProgramconsists of editing a file with an editor program

(normally known simply as an editor).A file name ending with the .java extension

indicates that the file contains Java source code. ◦ Eclipse (www.eclipse.org), ◦ NetBeans (www.netbeans.org),◦ JBuilder (www.borland.com), ◦ JCreator (www.jcreator.com), ◦ BlueJ (www.blueJ.org), ◦ jGRASP (www.jgrasp.org) ◦ jEdit (www.jedit.org).

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Phase 2: Compiling a Java Program into Phase 2: Compiling a Java Program into BytecodesBytecodes the programmer uses the command javac (the Java compiler) to compile a program. For

example, to compile a program called Welcome.java, you would type

javac Welcome.java

If the program compiles, the compiler produces a .class file called Welcome.class that

contains the compiled version of the program.

The Java compiler translates Java source code into bytecodes that represent the tasks to

execute in the execution phase (Phase 5). Bytecodes are executed by the Java Virtual

Machine (JVM)—a part of the JDK and the foundation of the Java platform.

A virtual machine (VM) is a software application that simulates a computer, but

hides the under- lying operating system and hardware from the programs that interact

with the VM.

the same VM is implemented on many computer platforms, applications that it executes can be used

on all those platforms.

bytecodes are platform-independent instructions—they are not dependent on a particular

hardware platform (>< machine codes).

->So Java’s bytecodes are portable—that is, the same bytecodes can execute on any

platform containing a JVM that understands the version of Java in which the bytecodes

were compiled.

The JVM is invoked by the java command.

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Phase 3: Loading a Program into Phase 3: Loading a Program into MemoryMemory the program must be placed in memory before it can execute

—known as loading.

java Welcome

The class loader takes the .class files containing the

program’s bytecodes and transfers them to primary memory.

The class loader also loads any of the .class files provided by

Java that your program uses.

The .class files can be loaded from a disk on your system or

over a network (e.g., your local college or company network,

or the Internet).

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Phase 4: Bytecode Phase 4: Bytecode VerificationVerificationas the classes are loaded, the bytecode

verifier examines their bytecodes to ensure that they are valid and do not violate Java’s security restrictions.

Java enforces strong security, to make sure that Java programs arriving over the network do not damage your files or your system (as computer viruses and worms might).

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Phase 5: ExecutionPhase 5: Execution the JVM executes the program’s bytecodes, thus performing the

actions specified by the program.

In early Java versions, the JVM was simply an interpreter for Java

bytecodes -> execute slowly. Today’s JVMs typically execute

bytecodes using a combination of interpretation and so-called just-in-

time (JIT) compilation.

Thus Java programs actually go through two compilation phases—

one in which source code is translated into bytecodes (for portability

across JVMs on different computer platforms) and a second in which,

during execution, the bytecodes are translated into machine language

for the actual computer on which the program executes.

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Compiling and executing the Compiling and executing the Java programJava program

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.

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Passing Command Line Passing Command Line ArgumentsArguments

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]);System.out.println(pargs [1]);System.out.println(pargs [2]);

}}

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Passing Command Line Passing Command Line ArgumentsArguments

Output

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Basics of the Java Basics of the Java Language Language

Classes & Methods

Data types

Variables

Constants

Operators

Control structures

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Classes in Java Classes in Java

Class declaration Syntax

class Classname {

var_datatype variablename;:

 met_datatype methodname(parameter_list):

}

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Sample classSample class

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Data Types Data Types

byte char boolean short int long float double

Array

Class

Interface

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Integer TypesInteger TypesThe integer types are for numbers without

fractional parts. Negative values are allowed.

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Floating-Point TypesFloating-Point TypesThe floating-point types denote numbers

with fractional parts

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The char TypeThe char Type•The char type is used to describe individual characters.

•For example, 'A' is a character constant with value 65.

•It is different from "A", a string containing a single character. Unicode code units can be

expressed as hexadecimal values that run from \u0000 to \uFFFF.

• For example, \u2122 is the trademark symbol (™) and \u03C0 is the Greek letter pi (π).

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The boolean TypeThe boolean Type The boolean type has two values, false and true. It is used for

evaluating logical conditions.

You cannot convert between integers and boolean values.

void bubbleSort(int[] x, int n) { boolean anotherPass; // true if something was out of order

do { anotherPass = false; // assume everything sorted for (int i=0; i<n-1; i++) { if (x[i] > x[i+1]) { int temp = x[i]; x[i] = x[i+1]; x[i+1] = temp; //

exchange anotherPass = true; // something wasn't sorted, keep going

} } } while (anotherPass);

}

void bubbleSort(int[] x, int n) { boolean anotherPass; // true if something was out of order

do { anotherPass = false; // assume everything sorted for (int i=0; i<n-1; i++) { if (x[i] > x[i+1]) { int temp = x[i]; x[i] = x[i+1]; x[i+1] = temp; //

exchange anotherPass = true; // something wasn't sorted, keep going

} } } while (anotherPass);

}04:42 PM

Type CastingType Casting

In type casting, a data type is converted into another data type.

Example float c = 34.89675f;

int b = (int)c + 10;

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Automatic type and Automatic type and CastingCasting

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.

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Type Promotion RulesType 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.

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VariablesVariablesThree components of a variable

declaration are:◦ Data type

◦ Name

◦ Initial value to be assigned (optional)

Syntaxdatatype identifier [=value][,

identifier[=value]...];

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Initializing VariablesInitializing Variables you must explicitly initialize it by means of an assignment

statement—you can never use the values of uninitialized variables.

the Java compiler flags the following sequence of statements as an

error:

int vacationDays;

System.out.println(vacationDays); // ERROR--variable not initialized

in Java you can put declarations anywhere in your code.

double salary = 65000.0;

System.out.println(salary);

int vacationDays = 12; // ok to declare a variable here

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ExampleExample

Output

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);}

}

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Scope and Lifetime of Scope and Lifetime of VariablesVariables

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.

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ExampleExampleclass ScopeVar{public static void main(String [] args){int num = 10;if ( num == 10){

// num is available in inner scopeint num1 = num * num;

System.out.println("Value of num and num1 are " + num + " " + num1);

}//num1 = 10; System.out.println("Value of num is " + num);

}}

Output

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ConstantsConstants use the keyword final to denote a constant.

public class Constants

{

public static void main(String[] args)

{

final double CM_PER_INCH = 2.54;

double paperWidth = 8.5;

double paperHeight = 11;

System.out.println("Paper size in centimeters: "

+ paperWidth * CM_PER_INCH + " by " + paperHeight * CM_PER_INCH);

}

} The keyword final indicates that you can assign to the variable once, and then its

value is set once and for all. It is customary to name constants in all uppercase.

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ConstantsConstants It is probably more common in

Java to want a constant that is

available to multiple methods

inside a single class. These are

usually called class constants.

You set up a class constant with

the keywords static final.

Note that the definition of the

class constant appears outside

the main method. Thus, the

constant can also be used in

other methods of the same

class.

public class Constants2

{

public static void main(String[] args)

{

double paperWidth = 8.5;

double paperHeight = 11;

System.out.println("Paper size in

centimeters: “ + paperWidth *

CM_PER_INCH + " by " + paperHeight *

CM_PER_INCH);

}

public static final double CM_PER_INCH =

2.54;

}

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Array DeclarationsArray Declarations

Three ways to declare an array are:

◦datatype identifier [ ];

◦datatype identifier [ ] = new datatype[size];

◦datatype identifier [ ] = {value1,value2,….valueN};

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Example – One Dimensional Example – One Dimensional ArrayArray

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

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Example – Multi Example – Multi Dimensional ArrayDimensional Arrayclass MultiArrayDemo

{public static void main ( String [] arg){

int multi[][] = new int [4][];multi[0] = new int[4];multi[1] = new int[4];multi[2] = new int[4];multi[3] = new int[4];int num = 0;for (int count = 0; count < 4; count++){

for (int ctr = 0; ctr < count+1; ctr++)

{multi[count][ctr] =

num;num++;

}}

for (int count = 0; count < 4; count++)

{for (int ctr = 0; ctr < count+1;

ctr++){

System.out.print(multi[count][ctr] + " ");

System.out.println();}

}}

}Output

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Operators Operators

Arithmetic Operators

Bitwise Operators

Relational Operators

Logical Operators

Conditional Operators

Assignment operators04:42 PM

Arithmetic OperatorsArithmetic 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.

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ExampleExampleclass 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);System.out.println("Value of num before the operation is : " + num);

num ++;System.out.println("Value of num after ++ operation is : " + num);double num3 = 25.75, num4 = 14.25, res;res = num3 - num4;System.out.println("num3 – num4 is : " +res);res -= 2.50;System.out.println("res -= 2.50 " + res);System.out.println("Value of res before -- operation is : "+ res);res--;System.out.println("Value of res after -- operation is : " + res);

}}

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Output

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Bitwise OperatorsBitwise Operators

A bitwise operator allows manipulation of

individual bits in an integral primitive data type.

These operators act upon the individual bits of their

operands.

Bitwise operators perform Boolean algebra on the

corresponding bits in the two arguments to produce

the result.

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The bitwise operators are

& (“and”) | (“or”) ^ (“xor”) ~ (“not”) These operators work on bit patterns. For example, if n is an integer

variable, then

int fourthBitFromRight = (n & 8) / 8; gives you a 1 if the fourth bit from the right in the binary representation of

n is 1, and 0 if not. Using & with the appropriate power of 2 lets you mask out all but a single

bit.

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Relational OperatorsRelational 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.

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ExampleExampleclass RelOp{

public static void main(String [] args){

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

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Logical OperatorsLogical OperatorsLogical operators work with Boolean

operands. Some operators are

◦&◦ |◦^◦!

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Conditional OperatorsConditional OperatorsThe 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”;

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Assignment OperatorsAssignment 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.

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Operator Precedence 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.

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Mathematical Functions and Mathematical Functions and ConstantsConstants The Math class contains an assortment of mathematical functions that you

may occasionally need, depending on the kind of programming that you do.

To take the square root of a number, use the sqrt method:

double x = 4;

double y = Math.sqrt(x);

System.out.println(y); // prints 2.0

The Java programming language has no operator for raising a quantity to a

power. You must use the pow method in the Math class.

double y = Math.pow(x, a);

Math.PI

Math.E

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Formatting output with Escape Formatting output with Escape Sequences 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

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Control FlowControl 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.

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Control Flow Structures in Control Flow Structures in JavaJava

Decision-making◦if-else statement◦switch-case statement

Loops◦while loop◦do-while loop◦for loop

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if-else statementif-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;

}04:42 PM

ExampleExampleclass CheckNum{public static void main(String [] args){int num = 10;if (num % 2 == 0)System.out.println(num + " is an even number");

elseSystem.out.println(num + " is an odd number");

}}

Output

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switch – case statementswitch – case statementThe 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.

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ExampleExampleclass SwitchDemo{

public static void main(String[] args){

int day = 4;String str;switch (day){

case 0: str = "Sunday";break;

case 1: str = "Monday"; break;

case 2: str = "Tuesday"; break;

case 3: str =

"Wednesday"; break;

case 4: str = "Thursday"; break;

case 5: str =

"Friday";

break;case 6:

str = "Saturday";

break;

default: str = "Invalid

day"; }

System.out.println(str);}

}Output

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while Loopwhile 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;

.

.

.

}

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ExampleExampleclass FactDemo{public static void main(String [] args){int num = 5, fact = 1;while (num >= 1){

fact *= num; num--;}System.out.println("The factorial of 5 is : " + fact);

}}

Output

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do – while Loopdo – 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);

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ExampleExampleclass DoWhileDemo{public static void main(String [] args){int count = 1, sum = 0;do{

sum += count;count++;

}while (count <= 100);System.out.println("The sum of first 100 numbers

is : " + sum);}

}

The sum of first 100 numbers is : 5050

Output

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for Loopfor Loop All loops have some common features: a counter variable that is initialized before the

loop begins, a condition that tests the counter variable and a statement that modifies

the value of the counter variable.

The for loop provides a compact format for incorporating these features.

Syntax:

for (initialization statements; condition; increment / decrement statements)

{

action statements;

.

.

}04:42 PM

ExampleExampleclass 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);}

}

The sum of first 5 odd numbers is : 25

Output

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Jump StatementsJump StatementsThree 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.

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ExampleExampleclass BrDemoAppl{

public static void main(String [] args){

for (int count = 1; count <= 100; count++)

{ if (count == 10)

break; System.out.println("The value of

num is : " + count); }

System.out.println("The loop is over");}

}

The value of num is : 1The value of num is : 2The value of num is : 3The value of num is : 4The value of num is : 5The value of num is : 6The value of num is : 7The value of num is : 8The value of num is : 9The loop is over

Output

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SummarySummary 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.

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Summary Contd…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.

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