Java Try Catch block

Question

I initially started programming in college and learnt vb.net. Now I have decided to make the move to Java and have some queries. In vb, the try catch statement is laid out as fo

Answer 1

The code that is on the page that is in link i have modified it with single exception. Problem here is that in this case you will not able to know that exception is where whether due to

IndexOutOfBoundsException or IOException

just you know that a exception occurs

import java.io.*;

import java.util.List;
import java.util.ArrayList;

public class ListOfNumbers {

    public static void main(String... s) {
        ListOfNumbers lon = new ListOfNumbers();
        lon.writeList();
    }

    private List list;
    private static final int SIZE = 10;

    public ListOfNumbers() {
        list = new ArrayList(SIZE);
        for (int i = 0; i < SIZE; i++) {
            list.add(new Integer(i));
        }
    }

    public void writeList() {
        PrintWriter out = null;

        try {
            System.out.println("Entering" + " try statement");

            out = new PrintWriter(new FileWriter("e://OutFile.txt"));
            for (int i = 0; i < SIZE; i++) {
                out.println("Value at: " + i + " = " + list.get(i));
            }
        } catch (Exception e) {
            System.err.println("Caught Exception: " + e.getMessage());

        } finally {
            if (out != null) {
                System.out.println("Closing PrintWriter");
                out.close();
            } else {
                System.out.println("PrintWriter not open");
            }
        }
    }
}

Let us understand the concept it is better to know why the code fails due to which particular type of exception whether

IndexOutOfBoundsException or IOException

Now The Code with handling of different Exception

import java.io.*;

import java.util.List;
import java.util.ArrayList;

public class ListOfNumbers {

    public static void main(String... s) {
        ListOfNumbers lon = new ListOfNumbers();
        lon.writeList();
    }

    private List list;
    private static final int SIZE = 10;

    public ListOfNumbers() {
        list = new ArrayList(SIZE);
        for (int i = 0; i < SIZE; i++) {
            list.add(new Integer(i));
        }
    }

    public void writeList() {
        PrintWriter out = null;

        try {
            System.out.println("Entering" + " try statement");

            out = new PrintWriter(new FileWriter("e://OutFile.txt"));
            for (int i = 0; i < SIZE; i++) {
                out.println("Value at: " + i + " = " + list.get(i));
            }
        } catch (IndexOutOfBoundsException e) {
            System.err.println("Caught IndexOutOfBoundsException: " +
                               e.getMessage());

        } catch (IOException e) {
            System.err.println("Caught IOException: " + e.getMessage());

        } finally {
            if (out != null) {
                System.out.println("Closing PrintWriter");
                out.close();
            } else {
                System.out.println("PrintWriter not open");
            }
        }
    }
}

Here we could come to know that whether it fails due to creation of file at location

e://OutFile.txt drive Not on my system

error printed as

Caught Exception: e:\OutFile.txt (The system cannot find the path specified) Entering try statement PrintWriter not open

Next Case

Now when i comment the line

list.add(new Integer(i));

import java.io.*;
import java.util.List;
import java.util.ArrayList;

    public class ListOfNumbers {

        public static void main(String... s) {
            ListOfNumbers lon = new ListOfNumbers();
            lon.writeList();
        }

        private List list;
        private static final int SIZE = 10;

        public ListOfNumbers() {
            list = new ArrayList(SIZE);
            for (int i = 0; i < SIZE; i++) {
                //    list.add(new Integer(i));
            }
        }

        public void writeList() {
            PrintWriter out = null;

            try {
                System.out.println("Entering" + " try statement");

                out = new PrintWriter(new FileWriter("OutFile.txt"));
                for (int i = 0; i < SIZE; i++) {
                    out.println("Value at: " + i + " = " + list.get(i));
                }
            } catch (IndexOutOfBoundsException e) {
                System.err.println("Caught IndexOutOfBoundsException: " +
                                   e.getMessage());

            } catch (IOException e) {
                System.err.println("Caught IOException: " + e.getMessage());

            } finally {
                if (out != null) {
                    System.out.println("Closing PrintWriter");
                    out.close();
                } else {
                    System.out.println("PrintWriter not open");
                }
            }
        }
    }

then it clearly says that it fails for index out of bound exception

Entering try statement Caught IndexOutOfBoundsException: Index: 0, Size: 0 Closing PrintWriter

So for the purpose of debugging the application properly and efficiently it is good.

I have created condition for the other type of exception

NoClassDefFoundError

java.lang.NoClassDefFoundError: ListOfNumbers
Caused by: java.lang.ClassNotFoundException: stackprac.ListOfNumbers
    at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
Exception in thread "main" Process exited with exit code 1.