Exceptional handling is one of the
best useful features provided by Java.
Exception can be any error that may
occur during the execution of the program.
Example: When user tries to
withdraw amount more than his account balance, an error occurs.
In Such situations instead of
ending the program abnormally, Exception handling is used to throw the valid
error messages to the end user.
The reasons for
an exception can be mainly categorized into three categories:
1.
User(client) error
2.
Developer error
3.
Hardware error.
Exceptions are
mainly divided into three categories
1.
Checked Exceptions
2.
Un checked Exceptions
3.
Error
Below is the hierarchy of
exceptions. Throwable is the root class for all exceptions.
Checked Exceptions:
v
Checked Exceptions are the exceptions which are
checked by compiler. I.e. our program will not compile if do not handle these
checked Exceptions.
v
All checked Exceptions are inherited from Exception
class
v
Checked exceptions can be handled either by
using try-catch block. Or by using throws keyword
v
Checked Exceptions are also called as Compile time Exceptions
Example:
In the below example user is trying
to read a file called ‘chckedException.txt’
in D drive. There is a chance giving wrong
location for the file.
File file=new File ("D: // chckedException.txt”);
FileReader fr = new FileReader (file);
To handle such situations, java
throws a compile time exception called FileNotFoundException
which should be handled by the developer while developing the code.
Developer can use either try catch
block or can choose to skip the exception handling by just throwing it using
throws keyword.
Solution 1:
public void readFile()
{
Try
{
File file=new File ("D: // chckedException.txt”);
FileReader fr = new FileReader (file);
}
Catch(FileNotFoundException ex)
{
System.out.println(“File
does not exist at the given location”);
}
}
Solution 2
public void readFile() throws Exception
{
File file=new File ("D: // chckedException.txt”);
FileReader fr = new FileReader (file);
}
