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1. Java Essentials for Hadoop

2. Agenda
What is Java ?
Features of Java
How Java Works
Java Data Types
Java Operators
Statements & Blocks in Java
Java Class
Java Basic Constructs
Creating an Object
Arrays

3. What is Java ?
Java is a high level programming language
developed by Sun Microsystems and
released in November 1995.
Java can be used to create complete
applications that may run on a single
computer or be distributed among servers
and clients in a network.
Java is Object-Oriented and follows the
principal of “write once run anywhere”
codes.

4. Features of Java
Simple
Object Oriented
Multithreaded
Distributed
Platform Independent
Secure
Robust

5. What is JDK and JRE ?
JDK
+
Development
tools
 Compiler
 Debugger
JRE
JVM
Utility
Classes

6. How Java Works ?
Source
Code
Byte
Code
JVM
JIT Compiler
Java
Interpreter
Runtime
System
Output of
the
program
Java Compiler
Hexadecimal format
It is used to speed up the execution
Converts total byte code
into machine code

7. Data Types
Data Type Size Default value
Boolean 1 bit False
char 2 bytes 'u0000'
byte 1 byte 0
short 2 bytes 0
int 4 bytes 0
long 8 bytes 0L
float 4 bytes 0.0f
double 8 bytes 0.0d
String(any object) - null
Primitive Data Types
Non-primitive Data Types
(Reference type)
1. Class Type
2. Interface Type
3. Array type

8. Operators
Provide a way to perform different operations on variables.
Operator Type operators
Assignment =
Arithmetic + , - , * , /
Relational < , > , <= , >= , == , !=
Logical && , || , !
Bitwise &, |, ^, >>, <<
Unary ++ , --, +, -, !

9. Statements & Blocks in JAVA
Statements are always terminated by
a semi-colon(;)
A block is a compound
statement enclosed in curly
brackets.
Statement forms a complete
command to be executed.
class Stat
{
Boolean flag ; //statement 1
Int x = 20 ; //Statement 2
.
.
}
Open braces for a block
End of block, using close braces

10. A class can be defined as a template/blue print that describes the
behaviors and states that object of its type support.
Objects have states and behaviors.
Example: Bicycles have state (current gear, current pedal cadence, two wheels,
number of gears) and behavior (braking, accelerating, slowing down, changing gears).
An object is an instance of a class.
Java Class

11. Example of a class
public class hello {
public static void main(String[] args)
{
int number = 10; //variable
System.out.println("Hello");
System.out.println(number);
}
}
class Myclass
{
//data members
//constructors
// methods or member functions
}

12. Method
Public static void myFunction(arg1, arg2, arg3)
{
}
Modifier
Java keyword
return type
function name
Any number of
arguments
//Body of the method

13. Public
• Can be accessed from anywhere.
Protected
• Can be accessed in the same package or any derived
class.
Default
• Can be accessed within the class only.
Private
• Can be accessed within the same package.
Modifiers

14. Java Basic Constructs
If…else case
Switch Case
Loops in Java – for loop, while loop,
do while loop

15. If Else - Syntax
If (condition)
{
Statements
}
else
{
Statements
}
Statements
true
false
condition

16. Switch - Syntax
Switch(x)
{
Case 1:
Statements
Case 2:
Statements
default :
Statements
}
Case 1
Statements
Statements
Case 2
true
false
true
false
default
End of the switch
Statement

17. For Loop - Syntax
for (initialization;
condition;
increment/decrement;)
{
statement 1;
statement 2;
…
}
Initialization
Inside the for loop
true
false
Increment/
decrement
End of for loop
condition

18. While Loop - Syntax
while (<condition>)
{
statement1;
…
}
Initialization
Inside the for loop
true
false
Increment/
decrement
End of for loop
condition

19. Do While Loop Syntax
do
{
statement 1;
statement 2;
……
} while (<condition>) ;
Initialization
Inside the do while loop
true
false
Increment/
decrement
End of for loop
condition
condition

20. Creation of the Object
Class_name object_name = new class_name();
Name of the class
Creates a reference object
Allocate memory
Constructor of the class
Creates a new object

21. An array is a list of similar elements.
An array has a fixed:
- name
- type
- length
These must be declared when the array is created.
Array size cannot be changed during the execution
of the code.
Arrays