What is finally block in java?

Answer 1

The Finally block in java is used along with the try-catch statements.

The usual structure is

try {

.....

} catch(Exception e){

....

} finally {

.....

}

In the finally block we usually have code that is used to perform clean up activities corresponding to the code in the try block. When an exception occurs in the try block control comes to the catch block and the rest of the code in the try block would not execute. In such cases we may need to have some code that cleans up the objects that we created/used in the try block.

No matter what happens, the code inside the finally block would definitely execute.

The best use of finally block is when we are connecting to the database. In the try block we would have the statements that instantiate the connection, prepared statement, result set etc. If the query fails then all these objects would be left open and the code would continue. So in the finally block we usually nullify these statements so that even in case of an error the unused objects are cleared.

Example:

Connection con;

PreparedStatment PS;

ResultSet rs;

try{

con = ConnectionManager.getConnection();

PS = con.prepareStatement(query);

rs = PS.executyQuery();

......

} catch (Exception e){

e.printStackTrace();

} finally {

con.close();

PS.close();

}

In case of an error the connection & prepared statement objects would remain open if we do not have the finally block.

Tip: Whatever code we have inside the finally block would be run definitely if the try block is invoked. We can even use the finally block to check if the try block was reached and executed. If the try executes then we can rest assured that the finally would also get executed.

Answer 2

Sun's Java Tutorial gives a few situations where a finally block will not execute.

"Note: If the JVM exits while the try or catch code is being executed, then the finally block will notexecute. Likewise, if the thread executing the try or catch code is interrupted or killed, the finally block willnot execute even though the application as a whole continues."

This method calls the exit method in class Runtime and terminates the JVM. This method never returns normally and finally is never called.

try {
System.out.println("hello");

System.exit(0);

} finally {

System.out.println("bye");

} // try-finally

Answer 3

Finally block is a block that is always executed . It is mainly used to perform some important tasks such as closing connection stream etc.

Answer 4

If you include system.exit(0); before the finally block in your code then execution flow will stop and finally block will not be executed.