Checked and Unchecked exceptions

In java, there are two types of exceptions we can find.

1.         Checked exceptions
2.       Unchecked exceptions

Checked exception:

Checked exceptions are checked at the compilation time. If some code contains checked exception, that exception should be handled using try catch block or throw using throws keyword.

Example :

Let’s say in a java program we open a file and try to read it. In there we have to use FileReader(). FileReader() throws an exception called “FileNotFoundException” . and also I there we have to use readLine() and close() methods. Those are also throws checked exception called “IOException”.

Sample code :

            import java.io.*;

class Main {

    public static void main(String[] args) {

        FileReader file = new FileReader("C:\\test\\a.txt");

        BufferedReader fileInput = new BufferedReader(file);

         

        // Print first 3 lines of file "C:\test\a.txt"

        for (int counter = 0; counter < 3; counter++)

            System.out.println(fileInput.readLine());

         

        fileInput.close();

    }

}

Output :

               Exception in thread "main" java.lang.RuntimeException: Uncompilable source code - 

unreported exception java.io.FileNotFoundException; must be caught or declared to be

thrown

         at Main.main(Main.java:5)

To fix this we have to use throws keyword or try-catch block.

Unchecked Exceptions :-

Unchecked exception are the exceptions which are not check in the compilation time. As an example, in C++, all exceptions are unchecked. So it is not forced by the compiler to handle or throw.

In Java, Errors and Run time Exception classes are unchecked. All others are checked.

Example :

                class Main {

   public static void main(String args[]) {

      int x = 0;

      int y = 10;

      int z = y/x;

  }

}

 Output :

        Exception in thread "main" java.lang.ArithmeticException: / by zero

         at Main.main(Main.java:5)

         Java Result: 1