Exception Handling

Education is not limited to just classrooms. It can be gained anytime, anywhere... - Ravi Ranjan (M.Tech-NIT)

Exception Handling in Java

  1. Exception Handling
  2. Advantage of Exception Handling
  3. Hierarchy of Exception classes
  4. Types of Exception
  5. Scenarios where exception may occur

The exception handling in java is one of the powerful mechanism to handle the runtime errors so that normal flow of the application can be maintained.

In this page, we will learn about java exception, its type and the difference between checked and unchecked exceptions.

What is exception

Dictionary Meaning: Exception is an abnormal condition.

In java, exception is an event that disrupts the normal flow of the program. It is an object which is thrown at runtime.

What is exception handling

Exception Handling is a mechanism to handle runtime errors such as ClassNotFound, IO, SQL, Remote etc.

Advantage of Exception Handling

The core advantage of exception handling is to maintain the normal flow of the application. Exception normally disrupts the normal flow of the application that is why we use exception handling. Let's take a scenario:

  1. statement 1;  
  2. statement 2;  
  3. statement 3;  
  4. statement 4;  
  5. statement 5;//exception occurs  
  6. statement 6;  
  7. statement 7;  
  8. statement 8;  
  9. statement 9;  
  10. statement 10;  

Suppose there is 10 statements in your program and there occurs an exception at statement 5, rest of the code will not be executed i.e. statement 6 to 10 will not run. If we perform exception handling, rest of the statement will be executed. That is why we use exception handling in java.

Do You Know ?

  • What is the difference between checked and unchecked exceptions ?
  • What happens behind the code int data=50/0; ?
  • Why use multiple catch block ?
  • Is there any possibility when finally block is not executed ?
  • What is exception propagation ?
  • What is the difference between throw and throws keyword ?
  • What are the 4 rules for using exception handling with method overriding ?

Hierarchy of Java Exception classes

hierarchy of exception handling

Types of Exception

There are mainly two types of exceptions: checked and unchecked where error is considered as unchecked exception. The sun microsystem says there are three types of exceptions:

  1. Checked Exception
  2. Unchecked Exception
  3. Error

Difference between checked and unchecked exceptions

1) Checked Exception

The classes that extend Throw able class except Runtime Exception and Error are known as checked exceptions e.g.IO Exception, SQL Exception etc. Checked exceptions are checked at compile-time.

2) Unchecked Exception

The classes that extend Runtime Exception are known as unchecked exceptions e.g. Arithmetic Exception, NullPointerException, and ArrayIndexOutOfBoundsException etc. Unchecked exceptions are not checked at compile-time rather they are checked at runtime.

3) Error

Error is irrecoverable e.g. Out Of Memory Error, Virtual Machine Error, Assertion Error etc.

Common scenarios where exceptions may occur

There are given some scenarios where unchecked exceptions can occur. They are as follows:

1) Scenario where Arithmetic Exception occurs

If we divide any number by zero, there occurs an Arithmetic Exception.

  1. int a=50/0;//ArithmeticException  

2) Scenario where Null Pointer Exception occurs

If we have null value in any variable, performing any operation by the variable occurs an Null Pointer Exception.

  1. String s=null;  
  2. System.out.println(s.length());//NullPointerException  

3) Scenario where NumberFormatException occurs

The wrong formatting of any value may occur Number Format Exception. Suppose I have a string variable that has characters, converting this variable into digit will occur NumberFormatException.

  1. String s="abc";  
  2. int i=Integer.parseInt(s);//NumberFormatException  

4) Scenario where ArrayIndexOutOfBoundsException occurs

If you are inserting any value in the wrong index, it would result ArrayIndexOutOfBoundsException as shown below:

  1. int a[]=new int[5];  
  2. a[10]=50//ArrayIndexOutOfBoundsException  

Java Exception Handling Keywords

There are 5 keywords used in java exception handling.

  1. try
  2. catch
  3. finally
  4. throw
  5. throws