JAVA EE: Java Tutorial : Java Exception handling (throws keyword)

Thursday 23 June 2016

Java Tutorial : Java Exception handling (throws keyword)

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Java Tutorial : Java Exception handling (throws keyword)

ThrowsDemo1.java

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.Scanner;

public class ThrowsDemo1
{
    public static void main(String[] args)
    {

        try
        {
            new ThrowsDemo1().getFileInfo();
        }
        catch (IOException e)
        {
            System.out.println("Exception handled.");
        }

        System.out.println("normal flow...");

    }

    private void getFileInfo() throws IOException
    {

        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter the fileName : ");
        String fileName = scanner.nextLine();
        scanner.close();

        /*
         * Wrap a BufferedReader around FileReader.
         */
        BufferedReader bufferedReader = new BufferedReader(
                new FileReader(fileName));

        /*
         * Use the readLine method of the BufferedReader to
         * read one line at a time. the readLine method
         * returns null when there is nothing else to read.
         */
        String line = null;

        while ((line = bufferedReader.readLine()) != null)
        {
            System.out.println(line);
        }

        // Close the BufferedReader when we're done.
        bufferedReader.close();
    }

}

Output

Enter the fileName : myfile.txt
Peter
David
Julia
normal flow...

---------------------------------

Enter the fileName : hi.txt
Exception handled.
normal flow...

ThrowsDemo2.java

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.Scanner;

public class ThrowsDemo2
{
    public static void main(String[] args)
    {

        try
        {
            new ThrowsDemo2().getFileInfo();
        }
        catch (FileNotFoundException exe)
        {
            System.out.println("Exception handled inside FileNotFoundException catch block.");
        }
        catch (IOException exe)
        {
            System.out.println("Exception handled inside IOException catch block.");
        }
        catch (Exception exe)
        {
            System.out.println("Exception handled inside Exception catch block.");
        }
         System.out.println("normal flow...");  

    }

    private void getFileInfo() throws FileNotFoundException,
            IOException, Exception
    {

        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter the fileName : ");
        String fileName = scanner.nextLine();
        scanner.close();

        /*
         * Wrap a BufferedReader around FileReader.
         */
        BufferedReader bufferedReader = new BufferedReader(
                new FileReader(fileName));

        /*
         * Use the readLine method of the BufferedReader to
         * read one line at a time. the readLine method
         * returns null when there is nothing else to read.
         */
        String line = null;
        
        while ((line = bufferedReader.readLine()) != null)
        {
            System.out.println(line);
        }

        // Close the BufferedReader when we're done.
        bufferedReader.close();
    }

}

Output

Enter the fileName : hi.txt
Exception handled inside FileNotFoundException catch block.
normal flow...

ThrowsDemo3.java

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.Scanner;

public class ThrowsDemo3
{
    public static void main(String[] args) throws IOException
    {

        new ThrowsDemo3().getFileInfo();
        System.out.println("normal flow...");

    }

    private void getFileInfo() throws IOException
    {

        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter the fileName : ");
        String fileName = scanner.nextLine();
        scanner.close();

        /*
         * Wrap a BufferedReader around FileReader.
         */
        BufferedReader bufferedReader = new BufferedReader(
                new FileReader(fileName));

        /*
         * Use the readLine method of the BufferedReader to
         * read one line at a time. the readLine method
         * returns null when there is nothing else to read.
         */
        String line = null;

        while ((line = bufferedReader.readLine()) != null)
        {
            System.out.println(line);
        }

        // Close the BufferedReader when we're done.
        bufferedReader.close();
    }

}

Output

Enter the fileName : hi.txt
Exception in thread "main" java.io.FileNotFoundException: hi.txt (The system cannot find the file specified)
    at java.io.FileInputStream.open0(Native Method)
    at java.io.FileInputStream.open(FileInputStream.java:195)
    at java.io.FileInputStream.<init>(FileInputStream.java:138)
    at java.io.FileInputStream.<init>(FileInputStream.java:93)
    at java.io.FileReader.<init>(FileReader.java:58)
    at ThrowsDemo3.getFileInfo(ThrowsDemo3.java:28)
    at ThrowsDemo3.main(ThrowsDemo3.java:11)