Exception Handling

An exception is a problem that arises during the execution of a program. Exception interrupt the normal flow of the program and the program/Application terminates abruptly

---

Types of Exception

As per sun microsystem there are three type of exception -

1.      Checked Exception

2.      Unchecked Exception

3.      Error

Checked Exception

Checked exception are mandatory to handle otherwise they will give time error like IOException, SQLException etc.

Code Snippet –

import java.io.File;

import java.io.FileInputStream;

import java.io.IOException;

/**

 * Example of checked exception

 * @author Manoj

 */

public class Exception {

 public static void main(String[] args) {

   try {

     FileInputStream fileInputStream  = new FileInputStream(new File("test.txt"));

     byte array[] = new byte[2014];

     fileInputStream.read(array);

     fileInputStream.close();

     } catch (IOException e) { //IOException need to capture or throws

           e.printStackTrace();

     }

  }

}

Unchecked Exception

Checked exception are not mandatory to handle means compiler will not give any error. ArithmeticException, NullPointerException, ArrayIndexOutOfBoundsException etc. are unchecked exceptions.

Error

Error is irrecoverable like OutOfMemoryError, VirtualMachineError, AssertionError etc.

---

Create custom exception-

Checked Exception –

To create checked exception extends Exception class

Unchecked Exception –

To create unchecked exception extends runtime exception class.

Code snippet-

/**

 * Custome Exception creation

 * @author Manoj

 */

public class CustomExceptionTest {

     public static void main(String[] args) {

           try {

                new CheckedException().createException();

           } catch (CheckedException e) {

                e.printStackTrace();

           }

           new UnCheckedException().createException();

     }

}

class CheckedException extends Exception {

     private static final long serialVersionUID = 1L;

     public void createException() throws CheckedException {

           throw new CheckedException();

     }

}

class UnCheckedException extends RuntimeException {

     private static final long serialVersionUID = 1L;

     public void createException() {

           throw new UnCheckedException();

     }

}

Note: - We can’t throw checked exception inside a lambda expression but we can unchecked exception.

Refer below code snippet:-

public void unCheckedException(){

     Map<Integer, Integer> dataMap = new HashMap<>();

     dataMap.forEach( (a,b) -> { throw new ArithmeticException();});

}

public void checkedException(){

     Map<Integer, Integer> dataMap = new HashMap<>();

     dataMap.forEach( (a,b) -> { throw new Exception();}); //compile time error Unhandled exception type Exception

}

public void checkedExceptionHandled(){

     Map<Integer, Integer> dataMap = new HashMap<>();

     dataMap.forEach( (a,b) -> { try {

           throw new Exception();

     } catch (Exception e) {

           // TODO Auto-generated catch block

           e.printStackTrace();

     }});

}

---

Throws exception after return will give compile time error:

public static int method() throws Exception {

     try {

           return 1;

           throw new NullPointerException(); //Unreachable code compiler error

     } catch (Exception exc) {

           throw new Exception();

     }

}