24-02-25
-----------
Q)Modify the above Java application(ReadingFromFile.java) so as to
implement exception handling.
Note:- Exception handling is implemented in the following application.
          file is closed in finally block.
//ReadingFromFile.java
import java.io.FileReader;
import java.io.IOException;
import java.io.FileNotFoundException;
class ReadingFromFile{
    public static void main(String[] args)  {
          FileReader fileReader=null;
		  try{
			 fileReader=new FileReader("one.txt");
		     int c=fileReader.read();
		     while(c !=-1){
		       System.out.print((char)c);
		       c=fileReader.read();
		    }	       
		}//try
		catch(FileNotFoundException e){
            System.out.println("Speciifed file not found");
		}
		catch (IOException e){
			System.out.println(e);
		}		
		finally{
			 try{
                if(fileReader!=null){
                   fileReader.close();
				}
             }
			 catch(IOException e){
				 System.out.println(e);
			 }
		}
	}//main
}//class

Note:- usage of finally is mandatory but causing serious coding inconvenience.
To overcome this probelm. "try with resources" is given by Java exception handling mechanism.

import java.io.FileReader;
import java.io.IOException;
import java.io.FileNotFoundException;
class ReadingFromFile{
    public static void main(String[] args)  {
   
		  try(FileReader fileReader=new FileReader("one.txt")){
		     int c=fileReader.read();
		     while(c !=-1){
		       System.out.print((char)c);
		       c=fileReader.read();
		     }//while     
		  }//try
		  catch(FileNotFoundException e){
                      System.out.println("Speciifed file not found");
		  }
		catch (IOException e){
		     System.out.println(e);
		}			
	}//main
}//class

Note:- try with resources  replaces finally block.

=>The try-with-resources statement is a try statement that declares one or more resources. 
=>A resource is an object that must be closed after the program is finished with it.
=>The try-with-resources statement ensures that each resource is closed at the end of the try statement.
=>Any object that implements java.lang.AutoCloseable, which includes all objects which implement java.io.Closeable, can be used as a resource.

Q)What is serialization?
    =>serialization is a mechansim of converting an object into a stream of bytes
    so that either it can be stored into a disk file or exported to a remote machine.

Q)What is persistence in the context of an object?
=>The mechansim of storing an object into a disk file is nothig but persistence.
=>Without serialization, an object can't be persisted.

Q)Develop a Java application in which, an object is persisted into a disk file.
import java.io.*;
class Employee implements Serializable{
	int empno;
	String name;
	Employee(int empno,String name){
         this.empno=empno;
		 this.name=name;
		 System.out.println("object created and initialized");
	}
	void displayEmployeeData(){
		System.out.println("EMPNO:"+empno);
		System.out.println("NAME:"+name);
	}
}
class PersistenceExample{
	public static void main(String[] args) throws IOException {
		Employee e=new Employee(101,"Rama");
		FileOutputStream fos=new FileOutputStream("emp.data");//binary output stream
		ObjectOutputStream oos=new ObjectOutputStream(fos);
		oos.writeObject(e);
		System.out.println("Object is stored into hard disk");
	}
}