Topic 4 Exception Handling Part II

7/30/2019 Topic 4 Exception Handling Part II

1/43

Programming Language (JAVA)

Unit 6.10 Exception Handling

Presentation2


2/43

Objectives

At the end of this presentation, you will be able to : Demonstrate the use of try, catch, finally blocks

List the built in exceptions

Create user defined exception


3/43

try block

The exceptions in a program are caught or

trapped using a try block.

A block of code which may generate anexception to terminate the program should be

placed inside the tryblock.


4/43

try block

Syntax

try

{

statements ;// code which generates exception

}


5/43

try block - Example

try

{

int A,B,C;A=Integer.parseInt(args[0]);

B=Integer.parseInt(args[1]);

C=A/B;

System.out.println(The value of C:- + C);

}


6/43

catch block

A try block should have at least one catchblock.

The try block may or may not generate anexception.

The catch block is responsible for catchingthe exception thrown from the try block.

Hence, a catch block is placed immediatelyafter a try block.


7/43

catch block

Syntax

catch(Exceptiontype object)

{

statements;// code which handles exception

}


8/43

catch block

Example

catch(ArithmeticException exp)

{

System.out.println(I have caught the

exception);

}


9/43

Exception Handling Mechanism


10/43

Hands-On!

Program excep1.javauses tryand catchblocks to handle the generated exception -

ArithmeticException


11/43

Hands-On!

Program ArrayExcepDemo.javageneratesArrayIndexOutOfBoundsException.


12/43

Activity 6.10.3

Fill in the blanks:

Step 1: Open the excep3.java file.

1. class excep32. {

3. public static void main(_______ args[])

4. {

5. int a=10,b=5,c=5,x=0;

6. _____


13/43


14/43

Activity 6.10.3 (Contd..)

Fill in the blanks:

12. System.out.println(The exception is caught);

13. }

14. System.out.println(The value of x is :- +x);

15. }

16. }

Step 2: Read the program and fill in the blanks withappropriate code.

Step 3: Save the program.

Step 4: Compile and execute it.


15/43

Activity 6.10.4

1. Give the output for program excep4.java.

Step 1: Open excep4.java file.

Step 2: Read the program, predict and write the

output.


16/43

Lab Exercise

1.Type the code of program error2.java.

class error2

{public static void main(String args[])

{

int a=Integer.parseInt(args[0]);int b=Integer.parseInt(args[1]);

int c=Integer.parseInt(args[2]);


17/43

Lab Exercise (Contd..)

int d=Integer.parseInt(args[3]);

double Result= a+b*c/d;

System.out.println(The value of theexpression is + Result);

}

}


18/43

Lab Exercise (Contd..)

1. Compile and execute the program error2.java

2. Enter positive values for a, b, c and d.

3. See the result.

4. Execute the program again and enter the valueof d as 0. An arithmetic exception occurs.

5. Add try and catch blocks to handle thisexception.

6. Compile, execute the program and see theresult.


19/43

Multiple Catch

Some times a code can generate more than

one type of exception.

If more than one type of exception arises,more than one catch statement should be

used to handle those exception types.


20/43

Hands-On!

Program MultiCatchDemo.javaillustrates theuse of multi catch statement.


21/43

Hands-On!

Program ExcepClassDemo.javaillustrates theuse ofExceptionclass to catch any type of

exception generated by the program.


22/43

Lab Exercise

2. Write a program to find the sum of 10

numbers in an array. Use try, catch block to

handle ArrayIndexOutOfBoundsException.


23/43

throw statement

The throw statement allows you to throw

exceptions that are not thrown by Java run-

time system. When throwis used inside the program, it

implies that the program is going to throw an

exception.


24/43

throw statement

Syntax

throw new exceptiontype ();


25/43

Hands-On!

Program throwdemo.javaillustrates the useof throw statement.


26/43

Activity 6.10.5

Fill in the blanks to complete the program thatthrows exception explicitly:

Step 1: Open the excep5.java student data file.

Step 2: Read the program and fill in the blanks withappropriate code.

1. _______ excep5

2. {

3. public static void main(String args[])

4. {

5. int a=5,b=10,c=0;


27/43

Activity 6.10.5 (Contd..)6. c = b/a;7. try8. {9. ________ new Exception(What will happen);10. }

11. catch(____________ ae)12. {13. System.out.println(The exception caught);14. }15. System.out.println(The value of c is :- +c);16. }

17. }

Step 3: Save the program.

Step 4: Compile and execute it.


28/43

finally

The finallyblock contains statements fordoing the final process such as de-allocationof memory etc.

It may be added immediately after the tryblock or after the last catchblock.

A try block should have at least one catch

block or finally block immediately following it.


29/43

finally

Syntax

finally

{

statements ;// code to be executed

}


30/43

Hands-On!

Program finallydemo.javademonstrates the

use of finally block.


31/43

Activity 6.10.6

Detect the errors in the following program:

Step 1: Open excep6.java student data file.

1. class excep62. {

3. public static void main(String args[])

4. {5. int a=0,b=5,c=0;

6. try

7. {


32/43


8. c=b/a;

9. }

10. catch(ArithemticException e)

11. {

12. System.out.println("Iam from catch block");

13. }


33/43


14. final

15. {

16. System.out.println("I am from finally block");

17. }

18. }

19. }

Step 2:Read the program and detect the errors in program.


34/43

Activity 6.10.7

Detect the errors in the following program:

Step 1: Open excep7.java student data file.

class excep7{

public static void main(String args[])

{int a[]={1,2};

try

{


35/43


if (a[1]>a[2])

System.out.println(a[1]);

Else

System.out.println(a[2]);

}

catch(ArrayIndexOutOfBoundsException e)

{


36/43


System.out.println("I am from catch block");

}

finally

{

System.out.println("I am from finally block");

}

}}

Step 2:Read the program and correct the mistakes.Step 3: Save, compile and execute the program.


37/43

Lab Exercise

3. Write a program to get 5 values of array

elements from the command line and print

those values in the main() method. Add trycatch blocks to handle

ArrayIndexOutOfBoundsException

4. Write a program to generate two exceptions

and catch using multiple catch blocks. Add a

finally block that prints The program is over.


38/43

User-Defined Exceptions

The built-in exceptions handle most of thecommon errors.

Certain application specific exceptions maynot be covered in the built-in exceptions.

Create a user-defined exception to handle thesituation.

Use exception handling mechanism to avoidthe abnormal program termination.


39/43

User-Defined Exceptions


40/43

Hands-On!

Program myexception.javaillustrates thecreation of User-Defined Exception.


41/43

Lab Exercise

5. Write a program to generate an exception

by your own (user defined exception) and

handle the exception.


42/43

Summary

In this presentation, you learnt the following:

finally block is used to handle any exception

generated by try block, even if the catchblock is not able handle the exception.

The finally block contains statements for

doing the final process such as de-allocationof memory etc.

The class Exception is the subclass of theclass Throwable.


43/43

Assignment

1. Define exception.

2. Write the syntax and example for a try

block.

3. Is it essential to capture all types of

exceptions?

4. What is the use of finally block?

Documents

Topic 4 Exception Handling Part II