Answer: In Java exception is an event that occurs during the execution
of the program that disrupts the normal flow of instruction. In Java API throwable is a parent class of all Exception and Error classes.
There are two types of exceptions CheckedExceptions ( known as Compile-time
exceptions) and
UncheckedExceptions
( known as runtimeExceptions) both type of exceptions extends Exception
class.
CheckException: Checked exceptions must
be explicitly caught or propagated as described in Basic try-catch-finally Exception Handling.
Example:
import java.io.File;
import java.io.FileReader;
File file=new
File("E://file.txt");
FileReader fr =
new FileReader(file);
}
}
If you try to compile the above program you will get
exceptions.”FileNotFoundException”, and which forces the programmer to catch them
explicitly.
UncheckedException : Unchecked exception is an exception that occurs at time of
execution, these include programming bugs such logic in error or in-proper used
API
Example:If you have declared an array 5 and trying to call 6th
element of the array the ArrayIndexOutOfBoundsExceptionexception .
public class ArrayOutBoundDemo{
public static void
main(String args[]){
int
num[]={1,2,3,4};
}
}
Error: indicate serious problems and abnormal
conditions that most applications should not try to handle. Error defines
problems that are not expected to be caught under normal circumstances by our
program. For example memory error, hardware error, JVM error etc.
see in below diagram The exception hierarchy in Java:
We can handle the java exception in three way:
Throw: Sometime we might want to generate exception explicitly
in our code, for example in a user authentication program we should throw
exception to client if the password is null. throw keyword is used to throw exception to
the runtime to handle it.
Throws: When we are throwing any exception in a method and not
handling it, then we need to use throws keyword, We can provide multiple
exceptions in the throws clause and it can be used with main() method.
Try-catch: Java try
block is used to enclose the code that might throw an exception. It must be
used within the method.
Syntax:
Try{
}catch(Exception e){
}finaly{
}
A catch statement involves declaring the type of exception you are
trying to catch. If an exception occurs in try block.In finally block is optional
and can be used only with try-catch block. Since exception halts the process of
execution, we might have some resources open that will not get closed, so we
can use finally block. finally block gets executed always, whether exception
occurred or not
