Topic 4 Exception Handling Part I

7/30/2019 Topic 4 Exception Handling Part I

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Programming Language (JAVA)

Unit 6.10 Exception Handling

Presentation1


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Revision

1. What are the two types of packages?

2. List some of the Java packages.

3. What is a user-defined package?


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Objectives

At the end of this presentation, you will be able to : Define the concept of Exception Handling

Mechanism

Define the use of try, catch and throw keywords.


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Error Handling

Errors are common during programming

They result in

Wrong Output

Abrupt termination of the program

Crashing of the system

These problems when left undetected, willcause big problems.

Java provides error handling mechanism tosolve these problems.


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Exceptions in Java

Exceptions are handled in Java using the fivekeywords

try

catch

throw

throws

finally


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Exception Handling Mechanism

tryblock

catchblock

finally

block

throw

Exception


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Types of Errors

Generally, in any language there are twobroad classification of errors:

Compile Time errors Errors that occur due to wrong syntax in the

program.

Detected by compilers and .class file not created.

Runtime errors

Errors that occur while executing a program.

The .class file are created but may not runproperly.


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Hands-On!

Program compileerrordemo.javademonstrates a compile time error.


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Activity 6.10.1

Correct the errors in the following program

and execute it:

Step 1: Open the file error1.java file.Step 2: Compile the program and observe the

errors.

Step 3: Correct the errors and save theprogram.

Step 4: Compile and execute the program.


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Hands-On!

Program runerrordemo.java demonstrates aruntime error.


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Activity 6.10.2

Identify why an error occurs while running

the following program:

Step 1: Open the file error2. java file.

Step 2: Compile the program and execute it.

Step 3: Observe the runtime error that occurs.

Step 4: Mention the cause for the error.


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Need for Exception Handling

It is a very important mechanism in all theprogramming languages.

The needs are :

To avoid abnormal program termination.

To avoid system crashes.

It helps to detect and report the exceptionalcircumstances, in order to take a necessaryaction.


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Types of Exceptions

Exception Type DescriptionArithmetic

Exception

Occurs when an abnormal

arithmetic condition occurs.ArrayIndexOutOf

BoundsException

Occurs when a program tries to

access an array element whose

index value is out of range

NumberFormat

Exception

Occurs when you try to convert a

string, which is not in the form of

a number into numeric.


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Exception Handling

Java provides superior support for exception

handling.

Java exception can be manually generated

by the code

by the Java runtime system during the program

execution.


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Throwable Sub classes


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try,catch, throw blocks

An exception is an object, which is generated

during the execution of the program.

When an exception arises an exceptionobject of that exception class is created and

thrown.

The exception which is thrown can be caughtinside the program to stop the abnormal

program termination.


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Summary

In this presentation, you learnt the following:

Exception handling is a very important

mechanism adopted by the programmingfield.

Generally in any language the errors are

broadly classified into two categories. Runtime errors are the errors which occur

during the execution period.


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Summary

In this presentation, you learnt the following:

Java exception can be manually generated

by the code or the Java runtime system cangenerate exception during the programexecution.

The exception types are subclass of theclass Throwable.

The class Throwable has two subclassesnamely Error and Exception.


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Assignment

1. Define exception.

Topic 4 Exception Handling Part I

Documents

Transcript of Topic 4 Exception Handling Part I