Java Essentials for Hadoop
Agenda
What is Java ?Features of JavaHow Java WorksJava Data TypesJava OperatorsStatements & Blocks in JavaJava Class Java Basic ConstructsCreating an ObjectArrays
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.
Features of Java
Simple
Object Oriented
Multithreaded
Distributed
Platform Independent
Secure
Robust
What is JDK and JRE ?
JDK
+
Development tools
Compiler Debugger
JRE
JVMUtility
Classes
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
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 TypesNon-primitive Data Types
(Reference type)
1. Class Type2. Interface Type3. Array type
Operators
Provide a way to perform different operations on variables.
Operator Type operators
Assignment =
Arithmetic + , - , * , /
Relational < , > , <= , >= , == , !=
Logical && , || , !
Bitwise &, |, ^, >>, <<
Unary ++ , --, +, -, !
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 1Int x = 20 ; //Statement 2..
}
Open braces for a block
End of block, using close braces
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
Example of a class
public class hello {public static void main(String[] args)
{int number = 10; //variableSystem.out.println("Hello");System.out.println(number);
}}
class Myclass{
//data members//constructors
// methods or member functions}
Method
Public static void myFunction(arg1, arg2, arg3){
}
Modifier
Java keyword
return type
function name
Any number of arguments
//Body of the method
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
Java Basic Constructs
If…else case
Switch Case
Loops in Java – for loop, while loop, do while loop
If Else - Syntax
If (condition){
Statements }
else{
Statements}
Statementstrue
false
condition
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
For Loop - Syntax
for (initialization; condition; increment/decrement;)
{statement 1;
statement 2; …
}
Initialization
Inside the for looptrue
false
Increment/decrement
End of for loop
condition
While Loop - Syntax
while (<condition>) {
statement1;…
}
Initialization
Inside the for looptrue
false
Increment/decrement
End of for loop
condition
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
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
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
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