What is Exception handling in Java

 Exception handling  is a powerful mechanism in java programming. Exception is a problem in the program of an application at run time and exception handling is a technique or mechanism to maintain the normal flow of the application.Directly we can point exception as a abnormal behavior of a program or an application. The exception could be at compile time or at run time, both can divide in the type of the exception.

                   

  Exception and Sub Classes of Exception Class

These are type of exception

1. Checked Exception
The checked exception is a compile time exception and the class with checked exception extends Throwable class except RuntimeException and the exceptions are IOException and SQLException etc.An example considers as, when we want to open a file in our program and that file is not exist then it is IOException.


2. Unchecked Exception
The exceptions which check at run time call the RuntimeException or checked Exception.In these we have fore types.
• ArrayIndexOutOfBoundException
Ex.-- int arr[]=new int[3];
         arr[6]=13;  // ArrayIndexOutOfBound


• ArithmeticException
Ex.-- a=4/0; // ArithmeticException


• NullPointerException
Ex.-- String str=null; 
         System.out.println(str.length()); // NullPointerException


• NumberFormatException
Ex.-- String str='g';
         int a=Integer.pareseInt(str); // NumberFormatException


3. Error
The errors are the basically mistakes by the programmers and could be the situation which can not be recoverable.Like mistyping the name of a method or variable name, is example of programmer mistake, OutOfMemoryError by the over flow of Stack is another type which is not recoverable but these are ignored at compile time. 

try-catch and finally blocks in exception handling 

In the try block we put the code which could generate an Exception in the program.The try block is a enclosing block of the suspected code for Exception generate or the code which can generate an Exception but try block should be with the catch or with the finally and catch both blocks to handle an Exception.

The catch block must use after to the try block to handle the Exception with the name of the Exception.In this series the finally block is optional.The finally block if in the it always executes.The finally block use normally for the cleaning up the code like close the database connections,closing the the file and close the network connections which should be close after the work.

here is a simple example of these blockes.

int a;

try{

a=4/0; // ArithmeticException

}

catch(ArithmeticException e1)
{
//body of catch block
}
finally
{
System.out.println("this is finally block");
}
catch have an parameter and the name of the exception same as the given example.multiple catch block can exist in a class for different type of exception.

Garbage collector

Garbage collection in java is a low priority thread that run's automatically.It run and destroy the objects that are not being referred to any variable.
We can request to run the garbage collector using System.gc(); but it is not guaranteed that it is request will full fill.

ex-

The ab in line 4  now eligible for garbage collection in these line code automatically by garbage collector.

Java Data Types

Litterls in Java

Data value that appears explicitly in our program are called Java Literals. The literals are stored in the variable's to use for long time.

The literals are comes under different types that could be integer,character,float,boolean,String and null type literals. I have given Example in image of four type literals.Lets take a look of rest types with them.

Integer Literals 
Integer Literals are the number type Literals.Like 2478 and -234 are the example of Integer Literals.
int a=25;

Float Literals
Float Literals are the Float type or real number Literals. 24.277 and -34.343 are example of Float Literals.
float fl=2.23;

Character Literals
Character Literals are Charecter type Literals. In that first you know about the ASCII values.The ASCII Character set include 128 character including the letters and Symbols.

Boolean Literals 
In java programming the 0 and 1 are also treated as literals.Where 0 is for false and 1 is equivalent to the true.
boolean active=true;

String Literals
Any group of charecters call the String Literals.Where the String Literals are the place where you can save any meaning full charecter set like name of a persone.
String name="Shiva";

Object-Oriented Programming in Java

If a problem is solving in the term's of classes and object's it is called object oriented programming.The object oriented programming satisfy some of  features like polymorphism,encapsulation,inheritance and  abstraction.

    Object oriented programming include's data and function's at a same place in the form of object's.java include package,interface's,classes and all the feature of object oriented programming to satisfy the object Oriented programming feature's.
    The object's are instance of the class.

 

The instance always has same fields and methods like class.

Java features

The Features which make's java as most power full language.

Simple:The java is a simple language because it has different simple features.The java codes are simple and does not contain any pointer concept in explicit way.Automatic memory allocation and deallocation with strong memory management provides us bug free system.

Performance:Garbage collector and lightweight thread process enhance the performance of java programs.An another technique of it that is just in time compilation technique that improves the performance of java programs.

Eliminating week point's of C:.It does not use memory pointers.Java does not use preprocessor.

Security:

Platform Independent or Portable:

Byte Code:Byte code are always the form of 0 and 1 that is ease to understood by any machine. 

JVM:Java vertual machine make's a java program platform independent .

Object Oriented:

Robust:

Multi Threading:

Architectural Nature:

Distributed and Dynamic:Java supports HTTP and FTP protocols and also supports other protocols like TCP/IP and IP protocol's.These protocols help's the java to enable for the network to use remote access.Different networking features with servlet and applet's on the internet.

Metadata:

Class

A class is a prescription for a particular kind of object.We can use the class definitions to create objects of that class type.Class is also an example of encapsulation because it include that feature.This is to create objects of that class type.That include all the component specified belonging to the class.

The thing's that we can include in our class definition are fields(variables),methods.

Similarly a class is a collection of entities that have similar characteristics or we can say that a class provides definition for an object.

      class Demo

         {

           int demo1;

           int demo2;

          void DemoMethod(int dm1,int dm2)

               {

                 demo1=dm1;

                 demo2=dm2;

                }

           void DemoShow()

               {

                 System.Out.println("Demo1:"+demo1"Demo2:"+demo2);

                }

            }

In this example Demo is name of a class and demo1,demo2 are variables and the DemoMethod, DemoShow are methods of Demo class.