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:
- statement 1;
- statement 2;
- statement 3;
- statement 4;
- statement 5;//exception occurs
- statement 6;
- statement 7;
- statement 8;
- statement 9;
- 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.
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:
- Checked Exception
- Unchecked Exception
Difference between checked and unchecked exceptions
1) Checked Exception
The classes that extend Throwable class except RuntimeException and Error are known as checked exceptions e.g.IOException, SQLException etc. Checked exceptions are checked at compile-time.
2) Unchecked Exception
The classes that extend RuntimeException are known as unchecked exceptions e.g. ArithmeticException, NullPointerException, ArrayIndexOutOfBoundsException etc. Unchecked exceptions are not checked at compile-time rather they are checked at runtime.
Error is irrecoverable e.g. OutOfMemoryError, VirtualMachineError, AssertionError etc.
Common scenarios where exceptions may occur
There are given some scenarios where unchecked exceptions can occur. They are as follows:
1) Scenario where ArithmeticException occurs
If we divide any number by zero, there occurs an ArithmeticException.
- int a=50/0;//ArithmeticException
2) Scenario where NullPointerException occurs
If we have null value in any variable, performing any operation by the variable occurs an NullPointerException.
- String s=null;
3) Scenario where NumberFormatException occurs
The wrong formatting of any value, may occur NumberFormatException. Suppose I have a string variable that have characters, converting this variable into digit will occur NumberFormatException.
- String s=“abc”;
- 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:
- int a=new int;
- a=50; //ArrayIndexOutOfBoundsException
Java Exception Handling Keywords
There are 5 keywords used in java exception handling.