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Java – An Introduction
• Programming language developed by Sun Microsystems in 1991.
• Originally called Oak by James Gosling
• Originally created for consumer electronics ( TV, VCR, Mobile Phone, etc.)
• Internet and Web was just emerging, so Sun turned it into a language of Internet
Programming.
• Pure Object oriented language
• Java is a whole platform, with a huge library, containing lots of reusable code, and
an execution environment that provides services such as

security

portability across operating systems

automatic garbage collection.
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Need for Java
• Many different types of controllers with different set of CPU are used in electronic
devices.
• The problem with C and C++ is that designed to be compiled for a specific target.
• An attempt to solve these problems, Gosling and others began work on a portable,
platform-independent language that on a variety of CPUs under differing
environments.
• Second force was the introduction of World wide web demand a language that
could useful in creating portable application.
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Java “White Paper” Buzzwords
• Simple
• Object Oriented - technique for programming that focuses on the data (= objects)
and on the interfaces to that object.
• Portable
• Architecture Neutral - By generating bytecode instructions, make it executable on
many processors, given the presence of the Java runtime system.
• Interpreted - Java interpreter can execute Java bytecodes directly on any machine.
• Network-Savvy - Java has an extensive library of routines for coping with TCP/IP
protocols like HTTP and FTP.
• High Performance – JIT Compiler monitor the code and optimize the code for speed.
• Robust - Emphasis on early checking for possible problems, later dynamic (runtime)
checking, and eliminating situations that are error-prone.
• Multithreaded
• Secure - intended to be used in networked/distributed environments.
• Dynamic
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Java Milestones
Year
Milestones
1990
Sun decided to develop a software that could be used for consumer
electronics. A project called Green Project created and head by James
Gosling.
1991
Explored Possibility of using C++, with some updates announced a new
language named “Oak”
1992
Demonstrate a new language to control a list of home appliances
1994
Team developed a new Web browser called “Hot Java” to locate and run
applets.
1995
Oak was renamed to Java. Companies such as Netscape, Microsoft
announced their support for Java
1996
Java became the language for Internet Programming and General
purpose OO language.
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Java Applications
Java is used to develop two types of application program:
•
Stand-alone applications
•
Web applications (applets)
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Java Environment
JDK
- Java Development Kit ( Program enable users to create java applications)
JRE
IDE
- Java Runtime Environment ( Software to run java programs)
- Eclipse, Jcreator, NetBeans
Setting Path
MyComputer -> Environment Variables ->Advanced -> Path -> C:\Jdk1.7\bin
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Sample Helloworld application
/* Simple Helloworld Java application */
class test
{
public static void main(String[] args)
{
System.out.println(“Helloworld Java”);
}
}
// save it as test.java
Compile : javac test.java
Execute : java test
Helloworld Java
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Process of Building and Running Java Applications
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Sample Java Execution
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Java is Compiled and Interpreted
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How different from compiled languages?
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Platform Independency
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Introduction to JVM
• JVM is the interpreter used to convert the byte code to machine code on the fly and
execute it.
• Byte code is optimized instruction set which independent of machine.
JVM Architecture
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JVM
Advantages
• Enable java program run in protected environment
• Write once, run anywhere (one size fits all)
• Browser can cache the downloaded code and reuse it later
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Spot the errors
1. Fix the errors
Class Demo
public static void Main(String[] args)
{
System.out.println("afternoon");
system.out.println("morning");
}
}
If a NoClassDefFoundError occurs when you run a program, what is the cause of the
error?
If a NoSuchMethodError occurs when you run a program, what is the cause of
the error?
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Spot the errors
2. Identify and fix the errors in the following code:
public class Welcome
{
public void main(string args[])
{
System.out.println('Welcome to Java!);
}
)
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Input Processing
import java.util
public class InputDemo
{
Scanner in;
public static void main(String[] args)
{
in=new Scanner(System.in);
System.out.println(“Enter a value”);
int i=in.nextInt();
System.out.println(“User has Entered :” + i );
}
}
nextLine, next, nextDouble, hasNext, hasNextInt, hasNextDouble
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Reading Input
Using Console class – Java.io
import java.util
public class InputDemo
{
public static void main(String[] args)
{
Console con= System.Console();
String name=con.readLine();
String pass=con.readPassword();
System.out.println(“User Name : “+name +” and Password :” + pass);
}
}
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Declaration rules for a Java file
 A source code file can have only one public class.
 If the source file contains a public class, the filename must match the public class
name.
 A file can have only one package statement, but multiple imports.
 The package statement (if any) must be the first (non-comment) line in a source file.
 The import statements (if any) must come after the package and before the class
declaration.
 If there is no package statement, import statements must be the first (noncomment) statements in the source file.
 package and import statements apply to all classes in the file.
 A file can have more than one nonpublic class.
 Files with no public classes have no naming restrictions.
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Class Access modifiers
 There are three access modifiers: public, protected, and private.
 There are four access levels: public, protected, default, and private.
 Classes can have only public or default access.
 A class with default access can be seen only by classes within the same package.
 A class with public access can be seen by all classes from all packages.
 Class visibility revolves around whether code in one class can
 Create an instance of another class
 Extend (or subclass), another class
 Access methods and variables of another class
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Java Tokens
Smallest individual units in a program are known as tokens. The compiler
recognizes them for building up expressions and statements.
A Java program is a collection of tokens, comments and white spaces.
Java language includes five types of tokens. They are:
1. Identifiers
2. Comments
3. Keywords
3. Literals
4. Operators
5. Separators
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Identifiers
Identifiers are programmer – designed tokens. They are used for naming classes,
methods, variables, objects, labels, packages and interfaces in a program. Java
identifiers follow the following rules:
• Identifiers must start with a letter, a currency character ($), or a connecting
character such as the underscore ( _ ).
• Identifiers cannot start with a number!
• After the first character, identifiers can contain any combination of letters, currency
characters, connecting characters, or numbers.
• In practice, there is no limit to the number of characters an identifier can contain.
• You can't use a Java keyword as an identifier.
• Identifiers in Java are case-sensitive; foo and FOO are two different identifiers.
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Legal and Illegal identifiers
Legal Identifiers
Illegal identifiers
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Naming Conventions
• Names of all public methods and instance variables start with a leading lowercase
letter. Example: average, sum
• When more than one word are used in a name, the second and subsequent words
are marked with a leading uppercase letters. Example: dayTemperature,
firstDayofMonth, totalMarks.
• All private and local variables use only lowercase letters combined with underscores
Example: length, batch_strength
• All classes and interfaces start with a leading uppercase letter(and each subsequent
word with a leading uppercase letter). Example: Student, HelloJava, Vehicle,
MototCycle
• Variables that represent constant values use all uppercase letters and underscores
between words. Example: TOTAL, F_MAX, PRINCIPAL_AMOUNT
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Comments
Comments help programmers to communicate and understand the program. They are
not programming statements and thus are ignored by the compiler. In Java, comments
are:
Line Comment – Statement preceded by two slashes (//)
Block Comment – Statement enclosed between /* and */
Java Document Comment – Statement enclosed between /**
*/
using Javadoc the document section converted to help files.
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Java Keywords
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Java Default Access Modifier
Default Access Modifier
Variable or method without access modifier is available to any class within
the same package. Variables inside interface are implicitly public and final and
methods in interface are public.
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Eight Primitives:
Eight primitives of java are:
Four of them are integer types; two are floating-point number types; one is the character type
char; and one is a Boolean type for truth values.
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Data Types:
Integer types :
Float types :
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Character Type
In order to store character constants in memory. Java provides a character data type
called char. The char type assumes a size of 2 bytes but, basically, it can hold only a single
character.
Boolean Type
Boolean type is used when we want to test a particular condition during the execution
of the program. There are only two values that a boolean type can take: true or false.
Remember, both these words have been declared as keywords. Boolean type is denoted by the
keyword boolean and uses only one bit of storage.
Variables
Variables is an identifier that denotes the storage location used to store a data value.
Variable declaration denotes three things:
• Type of the value the variable going to store.
• Based on the place of declaration the initial value assigned.
• Name of the variable to refer the value.
• Based on the type the size of memory allocation is determined.
Rules for variable declaration:
 Variable name must contain numbers, alphabets, and underscore symbol.
 They must not begin with a digit.
 Uppercase and lowercase are distinct. This means that the variable Total is not the same as
total or TOTAL.
 It should not be a keyword.
 White space is not allowed.
 Variable names can be of any length. A variable must be declared before it can be assigned a
value. A variable declared in a method must be assigned a value before it can be used.
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Variable
When a variable is assigned a value that is too large (in size) to be stored, it causes
overflow. Java does not report warnings or errors on overflow.
Example :
int value = 2147483647 + 1; // value will actually be -2147483648 ( causes overflow)
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Java variable types
Three types of variable used in java:
• Local variables ( declared inside function or construct)
• Instance variable ( Non static variable declared inside the class and accessed using
object)
• Static variable (declared with static modifier and accessed using class name).
Example:
class VariableDemo
{
int a=10;
static int b=20;
public static void main(String[] ar)
{
String c=“Hello”;
VariableDemo ob=new VariableDemo();
System.out.println(c + b + ob.a);
}
}
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Assignment Statements & Expression
variable can get the value using assignment statement or assignment expression.
Value is assigned using assignment operator
Example :
int a = 10;
An expression represents a computation involving values, variables, and operators
that, taking them together, evaluates to a value.
Example:
int x = 5 * (3 / 2) + 3 * 2;
Note: Java is strongly typed language i.e., variable on the left must be compatible with
the data type of the value on the right.
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Constants
Named constants or constant represent permanent data that never changes its value,
once gets initialized.
Example:
final double pi= 3.14;
Final indicate that you can assign to the variable once.
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Operators in Java
•
•
•
•
•
•
•
•
Arithmetic operators
Relational operators
Logical operators
Assignment operators
Increment and Decrement operators
Conditional operators
Bitwise logical operators
Special operators
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Arithmetic Operators
Relational Operators
Logical Operators
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Bitwise Operator
Example
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Assignment Operator
Assignment operators are used to assign the value of an expression to a variable. C# has a set
of ‘shorthand’ assignment operators which are used in the form
v op= exp
v
exp
op
-
is the variable
is the expression
is the binary operator
v op= exp is equivalent to v = v op(exp);
Ex:
x + = y + 1; is equivalent to x = x + (y +1)
Advantages:
. What appears on the left – hand side need not be repeated and
therefore it becomes easier to write.
. The statement is more concise and easier to read.
. The use of shorthand operators results in a more efficient code.
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Increment and Decrement Operator
The operators are ++ and - ++ means Increment Operator
- - means Decrement Operator
The operator ++ adds 1 to the operand while – subtracts 1. Both are unary operators and are
used in the following form:
++m; or
--m or
m++
m—
++m; is equivalent to m = m + 1 (or m + = 1;)
--m; is equivalent t o m = m – 1 (or m - = 1;)
We use the increment and decrement operators extensively in for and while loops
For Example:
Case 1
m = 5;
y = ++m;
Case 2
m = 5;
y = m--;
The statement
a [ i ++ ] = 10; is equivalent to
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a [ i ] = 10;
i = i + 1;
Conditional Operator
It is also known as Ternary operator
Syntax:
exp_1? exp_2: exp_3
Example
Special Operators
Instanceof Operator
The instanceof is an object reference operator and returns true if the object on the
left – hand side is an instance of the class given on the right – hand side. This operator allows us
to determine whether the object belongs to a particular class or not.
Example:
person
instanceof
student
Dot Operator
The dot operator (.) is used to access the instance variables and methods of class
objects.
Example:
person1.age
person1.salary( )
//Reference to the variable age
//Reference to the method salary( )
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Decision Making Statements
Two types of Decision making statements in java:
• If else
• Switch
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If Statement ( one way if statement)
Consists of a Boolean condition followed by one or statement.
Syntax:
if(Boolean_expression)
{
//Statements will execute if the Boolean expression is true
}
Example: Problem statement
Calculate the area of the circle in case of radius is positive integer
class Area
{
public static void main(String[] ar)
{
Scanner s=new Scanner(System.in);
int rad=s.nextInt();
if(rad>0)
{
System.out.println( “ the area is “ + (3.14 * rad * rad));
}
}
}
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Two way if statement
When there are multiple conditions need to be evaluated then we can use if-else construct. If
the condition is true one set of statement executes otherwise alternate set get executed.
Syntax:
if (boolean-expression) {
statement(s)-for-the-true-case;
}
else {
statement(s)-for-the-false-case;
}
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Nested if structure
Nested if structure come into play when there are too many alternate conditions to
be evaluated.
Syntax:
if (boolean-expression)
{
if (boolean-expression)
{
statement(s)-for-the-true-case;
}
}
else
{
statement(s)-for-the-false-case;
}
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Nesting if…else statement
if (Boolean-expression)
{
True-block statement(S)
if (Boolean-expression)
{
True-block Statement(s)
}
else
{
False-block Statement(s)
}
}
else
{
False-block statement(s)
}
else if Ladder:
if (condition_1)
Statement_1;
else if (condition_2)
Statement_2;
else if (condition_3)
Statement_3;
.
.
.
else if (condition_n)
Statement_n;
else
Default-Statement-x;
Common errors in Selection statement
1. Forgetting Necessary Braces
2. Wrong Semicolon at the if Line
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Common errors in Selection statement
3. Redundant Testing of Boolean Values
4. Dangling else Ambiguity
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Scenario to write if else:
1.
2.
Code to check whether the number entered by user is even or odd number.
Body Mass Index (BMI) is a measure of health on weight. It can be calculated by taking your weight in
kilograms and dividing by the square of your height in meters. The interpretation of BMI for people 16
years or older is as follows:
3.
Computing taxes : The United States federal personal income tax is calculated based on filing status
and taxable income. There are four filing statuses: single filers, married filing jointly, married filing
separately, and head of household. The tax rates vary every year. Table 3.2 shows the rates for 2009. If
you are, say, single with a taxable income of $10,000, the first $8,350 is taxed at 10% and the other
$1,650 is taxed at 15%. So, your tax is $1,082.5
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Scenarios
Lottery : Suppose you want to develop a program to play lottery. The program randomly
generates a lottery of a two-digit number, prompts the user to enter a two-digit number, and
determines whether the user wins according to the following rule:
1. If the user input matches the lottery in exact order, the award is $10,000.
2. If all the digits in the user input match all the digits in the lottery, the award is $3,000.
3. If one digit in the user input matches a digit in the lottery, the award is $1,000.
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Switch case
A switch statement allows a variable to be tested for equality against a list of values. Each value
is called a case, and the variable being switched on is checked for each case. If statement makes
a problem difficult, when too many choices are there to evaluate in such circumstances switch
is the alternative.
Syntax:
switch(expression)
{
case value :
//Statements
break;//optional
case value :
//Statements
break;//optional
default://Optional
//Statements
}
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THE SWITCH STATEMENT
switch (expression)
{
case value_1:
block_1;
break;
case value_2:
block_2;
break;
case value_3:
block_3;
break;
------------------------------------------default:
default_block
break;
}
Statement_x;
Rules for switch
• The switch-expression must yield a value of char, byte, short, or int type and must always be
enclosed in parentheses.
• The value1, and valueN must have the same data type as the value of the switch-expression.
Note that value1, and valueN are constant expressions, meaning that they cannot contain
variables, such as 1 + x.
• When the value in a case statement matches the value of the switch-expression, the
statements starting from this case are executed until either a break statement or the end of
the switch statement is reached.
• The keyword break is optional. The break statement immediately ends the switch statement.
• The default case, which is optional, can be used to perform actions when none of the
specified cases matches the switch-expression.
• The case statements are checked in sequential order, but the order of the cases (including
the default case) does not matter. However, it is good programming style to follow the
logical sequence of the cases and place the default case at the end.
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Scenario
Scissorrock-paper game: The program randomly generates a number 0, 1, or 2 representing
scissor, rock, and paper. The program prompts the user to enter a number 0, 1, or 2 and
displays a message indicating whether the user or the computer wins, loses, or draws.
In a “main” method, generate a random integer between 1 and 13 to represent the possible
values in a suit of playing cards.
• Use a “switch” statement that applies cases to your random integer.
• If the random number is 1, print out “Ace” to the console.
• If the random number is 11, print out “Jack” to the console.
• If the random number is 12, print out “Queen” to the console.
• If the random number is 13, print out “King” to the console.
The default case should simply print the random integer to the console.
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Conditional Expression
When we want to assign a value to a variable based on certain condition to be evaluated, the
we can use conditional expression.
Syntax:
X= boolean-expression ? expression1 : expression2;
Example :
To find the biggest of two numbers:
class Big
{
public static void main(String[] ar)
{
int a=Integer.parseInt(ar[0]);
int b=Integer.parseInt(ar[1]);
if(a>b)
System.out.println ( “ a is big “);
else
System.out.println ( “ b is big “);
}
//replaced entire if statement
int res = ( a > b ) ? a : b ;
}
Replaced by:
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Exercises
1. Rewrite the following statement using a conditional expression:
if (temperature > 90)
pay = pay * 1.5;
else
pay = pay * 1.1;
2. Write a program that prompts the user to enter the month and year and displays the
number of days in the month. For example, if the user entered month 2 and year 2000, the
program should display that February 2000 has 29 days. If the user entered month 3 and year
2005, the program should display that March 2005 has 31 days.
3. Write a program that prompts the user to enter an integer and checks whether the number
is divisible by both 5 and 6, or neither of them, or just one of them. Here are some sample
runs for inputs 10, 30, and 23.
4. What is y after the following switch statement is executed?
x = 3; y = 3;
switch (x + 3) {
case 6: y = 1;
default: y += 1; }
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5. Use a switch statement to rewrite the following if statement and draw the flow chart for
the switch statement:
if (a == 1)
x += 5;
else if (a == 2)
x += 10;
else if (a == 3)
x += 16;
else if (a == 4)
x += 34;
6. Write a switch statement that assigns a String variable dayName with Sunday, Monday,
Tuesday, Wednesday, Thursday, Friday, Saturday, if day is 0, 1, 2, 3, 4,5, 6, accordingly.
7. Rewrite the following if statement using the conditional operator:
if (count % 10 == 0)
System.out.print(count + "\n");
else
System.out.print(count + " ");
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Loops
• Loop is control structure that executes the sequence statement multiple times based on
condition. Java supports three different set of iteration statements such as:
 While loop
 Do – While loop
 For loop
 foreach loop
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While loop
• Based on conditional expression inside the loop, the set of statements get executed multiple
times
Syntax:
initialization;
while(test_condition)
{
Body of the Loop
}
Example:
Counting of numbers 1 to 100
//code
int sum, count=0;
while(count<100)
{
sum+=count;
count++;
}
S.O.P(count);
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Do-While loop
do-while loop is a variation of the while loop. The do-while loop executes the loop body first,
then checks the loop continuation-condition to determine whether to continue or terminate
the loop.
Syntax :
do {
// Loop body;
Statement(s);
} while (loop-continuation-condition);
Tip: Use the do-while loop if you have statements inside the loop that must be executed at
least once.
import java.util.Scanner;
public class TestDoWhile {
public static void main(String[] args) {
int data, sum = 0;
Scanner input = new Scanner(System.in);
System.out.print("Enter an int value (the program exits if the input is 0): ");
data = input.nextInt();
sum += data;
System.out.println("The sum is " + sum);
}}
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For Loop
A for loop is a repetition control structure that allows you to efficiently write a loop that needs
to execute a specific number of times.
Syntax:
for (initialization;test_condition;increment)
{
Body of the Loop
}
Example:
public class Test
{
public static void main(String args[])
{
for(int x =10; x <20; x = x+1)
{
System.out.print("value of x : "+ x );
System.out.print("\n");
}
}
}
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Enhanced for loop
Syntax:
for(declaration : expression)
{ //Statements }
Declaration:
The newly declared block variable, which is of a type compatible with the elements of the array
you are accessing. The variable will be available within the for block and its value would be the
same as the current array element.
Expression:
This evaluates to the array you need to loop through. The expression can be an array variable or
method call that returns an array.
Example:
public class Test
{
public static void main(String args[])
{
for( String s : args)
{
System.out.println(s);
}
}
}
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Scenario
1. Write a code to reverse the number using while loop.
2. Greatest Common divisor: Let the two input integers be n1 and n2. You know that number 1
is a common divisor, but it may not be the greatest common divisor. So, you can check
whether k (fork 2, 3, 4, and so on) is a common divisor for n1 and n2, until k is greater than n1
or n2. Store the common divisor in a variable named gcd. Initially, gcd is 1. Whenever a new
common divisor is found, it becomes the new gcd.
3. Predicating the Future Tuition: Suppose that the tuition for a university is $10,000 this year
and tuition increases 7% every year. In how many years will the tuition be doubled?
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Review Questions
Analyze the following code. Is count < 100 always true, always false, or sometimes true or
sometimes false at Point A, Point B, and Point C?
int count = 0;
while (count < 100) {
// Point A
System.out.println("Welcome to Java!\n");
count++;
// Point B
} // Point C
How many times is the following loop body repeated? What is the printout of the loop?
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What are the differences between a while loop and a do-while loop? Convert the following
while loop into a do-while loop.
int sum = 0;
int number = input.nextInt();
while (number != 0) {
sum += number;
number = input.nextInt();
}
Do the following two loops result in the same value in sum?
Can you always convert a while loop into a for loop? Convert the following while loop into a
for loop.
int i = 1, sum = 0;
while (sum < 10000) {
sum = sum + i;
i++;
}
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Suppose the input is 2 3 4 5 0. What is the output of the following code?
import java.util.Scanner;
public class Test {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
int number, max;
number = input.nextInt();
max = number;
while (number != 0) {
number = input.nextInt();
if (number > max)
max = number;
}
System.out.println("max is " + max);
System.out.println("number " + number);
}}
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What is the keyword break for? What is the keyword continue for? Will the following program
terminate? If so, give the output.
The for loop on the left is converted into the while loop on the right. What is
wrong? Correct it.
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After the break statement is executed in the following loop, which statement is executed?
Show the output.
for (int i = 1; i < 4; i++) {
for (int j = 1; j < 4; j++) {
if (i * j > 2)
break;
System.out.println(i * j);
}
System.out.println(i);
}
After the continue statement is executed in the following loop, which statement is executed?
Show the output.
for (int i = 1; i < 4; i++) {
for (int j = 1; j < 4; j++) {
if (i * j > 2)
continue;
System.out.println(i * j);
}
System.out.println(i);
}
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Identify and fix the errors in the following code:
public class Test {
public void main(String[] args)
{
for (int i = 0; i < 10; i++);
sum += i;
if (i < j);
System.out.println(i)
else
System.out.println(j);
while (j < 10);
{
j++;
};
{
j++;
} while (j < 10)
}
}
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What is wrong with the following code?
• Write a program that displays all the numbers from 100 to 1000, ten per line, that are
divisible by 5 and 6.
• Use a while loop to find the smallest integer n such that n2 is greater than 12,000.
• Write a program that reads an integer and displays all its smallest factors in increasing
order. For example, if the input integer is 120, the output should be as follows: 2, 2, 2, 3, 5.
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• Write a program that displays all the numbers from 100 to 1000, ten per line, that
are divisible by 5 and 6.
• Use a while loop to find the smallest integer n such that n2 is greater than 12,000.
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Array
• An array is a data structure which defines an ordered collection of a fixed number
of homogeneous data elements
• The size of an array is fixed and cannot increase to accommodate more elements
• In Java, array are objects and can be of primitive data types or reference types
• All elements in the array must be of the same data type
Creating an Array
1. Declaring the array
2. Creating memory locations
3. Putting values into the memory locations.
1. Declaration of Arrays
Syntax: type [ ] arrayname;
Example:
int [ ] counter;
float [ ] marks;
int [ ] x,y;
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Introduction
• An array is a group of like-typed variables that are referred to
by a common name.
• Arrays of any type can be created and may have one or more
dimensions.
• A specific element in an array is accessed by its index.
• Arrays offer a convenient means of grouping related
information.
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2. Creating memory locations
Syntax:
arrayname = new type [size];
Examples:
number = new int [5];
average = new float [10];
3. Declaration and Creation in one step
Syntax:
type [ ] arrayname = new type [size];
Examples:
int [ ] number = new int [5];
4. Initialization of Arrays
Syntax:
type [ ] arrayname = {list of values};
Example:
int [ ] number = {32,45,34,56,34};
int [ ] number = new int [3] {10,20,30};
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Alternative Array Declaration Syntax
int al[] = new int[3];
int[] a2 = new int[3];
The following declarations are also equivalent:
• char twod1[][] = new char[3][4];
• char[][] twod2 = new char[3][4];
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Array Representation
public class TestArray {
public static void main(String[] args) {
double[] myList = {1.9, 2.9, 3.4,1.5};
// Print all the array elements
for (double element: myList) {
System.out.println(element);
}}}
Output:
1.9
2.9
3.4
3.5
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One-Dimensional Arrays
• A one-dimensional array is a list of like-typed variables.
• To create an array you first must create an array variable of the
desired type.
• The general form of a one- dimensional array declaration is
• Syntax:
type var-name[ ]
Example
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Multidimensional Arrays
• In Java, multidimensional arrays are actually arrays of arrays.
• To declare a multidimensional array variable, specify each
additional index using another set of square brackets.
example,
• int twoD[][] = new int[4][5];
• Example
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Variable – Size Arrays
Variable – Size array is called Array of Array or Nested Array or Jagged Array
Ex:
int [ ] [ ] x = new int [3] [ ]; //Three rows array
x [0] = new int [2]
x [1] = new int [4]
x [2] = new int [3]
//First Rows has two elements
//Second Rows has four elements
//Third Rows has three elements
x[0]
x[0] [1]
x[1]
x[1] [3]
x[2]
x[2] [2]
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public class MyArrayc2
{
public static void main(String args[ ])
{
Scanner s=new Scanner(System.in);
int[][] jag=new int[3][];
jag[0]=new int[4];
jag[1]=new int[3];
jag[2]=new int[5];
System.out.println("Enter the array elements");
for(int i=0;i<jag.length;i++)
{
for(int j=0;j<jag[i].length;j++)
jag[i][j]=s.nextInt();
}
for(int i=0;i<jag.length;i++)
{
for(int j=0;j<jag[i].length;j++)
{
System.out.print(jag[i][j] + "\t ");
}
System.out.println();
}
}
}
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Variable length arguments
Java allows us to pass a variable number of arguments of the same type to a method.
The parameter in the method is declared as follows:
typeName... parameterNames
Rules:
A function should contain only one variable length parameter
The variable length parameter must be last in the list
Preceded by any number usual parameters.
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import java.util.*;
class vArgu
{
public static void printMax(int... numbers )
{
for (int i = 0; i < numbers.length; i++)
{
System.out.println( numbers[i] );
}
}
public static void main(String[] ar)
{
printMax(1,2,3,4,5);
}
}
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Example Problems
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How to sort an array and search an element inside it?
How to sort an array and insert an element inside it?
How to determine the upper bound of a two dimentional array?
How to reverse an array?
How to write an array of strings to the output console?
How to search the minimum and the maximum element in an array?
How to merge two arrays?
How to fill (initialize at once) an array?
How to extend an array after initialisation?
How to sort an array and search an element inside it?
How to remove an element of array?
How to remove one array from another array?
How to find common elements from arrays?
How to find an object or a string in an Array?
How to check if two arrays are equal or not?
How to compare two arrays?
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Quiz
1)What is the output of this program?
class array_output {
public static void main(String args[]) {
int array_variable [] = new int[10];
for (int i = 0; i < 10; ++i) {
array_variable[i] = i;
System.out.print(array_variable[i] + " ");
i++; } } }
2) class evaluate {
public static void main(String args[]) {
int arr[] = new int[] {0,1, 2, 3, 4, 5, 6, 7, 8, 9};
int n = 6;
n = arr[arr[n] / 2];
System.out.println(arr[n] / 2);
} }
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JAR File and Class Path
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Introduction
• The JAR file format is a compressed format used primarily to distribute Java
applications and libraries.
• It is built on the ZIP file format, and functions in a similar way
• Many files are compressed and packaged together in a single file, making it easy to
distribute the files over a network
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Path & ClassPath
• PATH and CLASSPATH are operating system level
environment variables.
• PATH is used to define where the system can find the
executables (.exe) files
– Example path= c:\program files\java\jdk.7.0_05\bin
• CLASSPATH is used to specify the location of .class files
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JAR
Steps to create jar File:
create a java code save the file
compile the java files to create .class files
create a manifest
manifest is the description contains the main
class header
Example: Main-Class: classname
save it in .mft extension
create jar
java cfm name.jar manifest.mft *.class
Executing the jar
java –jar name.jar
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