throw and catch exceptions?

[radhika743]

Friends, Can anybody explain me,"How do you throw and catch exceptions?"

[surekhav]

Hi Radhika,
U actually put the part of code where there is a chance of exception into a try block and after closing the try block u have ur catch block where u ll be having the message to be printed abt the exception
For eg:
in Data base connectivity
We have many possible exceptions to occur for connection itself
So we usually put the connection establishment in try block

public static Connection getConnection()
{
Connection con=null;
try
{
String ConnectionString=jdbc:oracle:thinDatabaseName:port number:oracl;
DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());
con=DriverManager.getConnection(ConnectionString,username,password);
}
catch(Exception e)
{
System.err.println(e);//Prints the exception
}
return con;//returns the connection
}

}


Friends correct me if i'm wrong

[hemanthjava]

hi the question asked was How do you throw and catch exceptions. We use a "throws:" clause in th method header declaration and catch the exception thrown either in the same method or in the super class invoking method.

For more information check out

Java Exception Handling

[PrashanthU]

Radhika...

NOTE : There is some problem while i post using angular brackets so..plz...find <

Hope you are aware of the keywords that you come across Exception Handling...that include : try,catch,finally blocks..throw,throws..clauses...

The below explanation is in view that you are aware of the differences between 'throw' and 'throws'...

We generally come across or use 'throw' when we wish to throw an object of an Exception ( here the exception object thrown will be of the user defined exception class which has to extend the 'Exception' class under the 'Run-time Exception' class which in turn is under the top most exception class 'Throwable' class )....
----------------------
1) First you have to define your own exception class depending upon the requirement extending the Exception class...
as
class &lt:user-defined-exception> extends Exception
{
//....
}
2)During the main code which you will obviously be placing in the 'try' block...for handling specific exceptions...so somewhere in the main code you you have to handle user defined exception in which case you 'throw' and object of that corresponding user-defined-exception..which has to be caught (handled) by 'catch' block...

A simple way of doing it...

SYNTAX:
public class
{
public static void main(String args[])
{
try
{
//statements...

throw new &lt:user-defined-exception>();
}
catch( <user-defined exception> ref-var)
{
//handle the exception by printing custom message or call a method from the user-defined exception class
}
}

[rk_ramakrishnamca]

well said prashantu, I have a small doubt, what is difference between the throw and throws keywords?

[PrashanthU]

Ramakrishna..

On observing one can atleast infer some differences b/w 'throw' and 'throws'
throw --- an action explicitly done
throws --- probability of occurrence of an action

As i said 'throw' is generally used to throw an object of user-defined exception and handle accordingly...where as 'throws' is specified as part of a method definition which has the probability of throwing some Unchecked exceptions and has to be handled by the programmer...in general we use 'throws' clause during File I/O operations,Database Connectivity...

SYNTAX:

void method-name() throws exception1,exception2...
{
//
}

[rk_ramakrishnamca]

Thank you prashantu.