What is difference between final, finally and finalize method is
asked to my friend in a Java
interview with one of the US based Investment bank. Though it was just a
telephonic round interview, he was asked couple of good questions e.g. how
to avoid deadlock in Java, How
get() method of HashMap works and one of the puzzle which is based on
recursion. In short final keyword can be used along with variable,
method and class and has different meaning for all of them. finally is another
Java keyword which is used in Exception handling along with try, catch, throw
and throws. finalize() is a special method in Java which
is called by Garbage
Collector before reclaiming GC eligible objects. In this Java interview
questions article we will compare final
vs finally vs finalize and highlight some important difference between final, finally and finalize method in
Java.
final vs finally vs finalize in Java
As I said earlier final keyword can be used along with variable,method and Class
in Java. If you make a variable final, you can
not change it's value, it will act like a constant. final variables
are initialized at the time of creation except in case of blank final variable which is initialized in Constructor. If you make a method
final in Java, you can not override
it in sub class . If you make a class final means it
can not be sub classed. Making a class final automatically makes all its method
final and this is sometime required due to security reason, This is one of the
reason Why
String is final in Java. In short final is not related at all with either finally or finalize keyword. final
keyword also help to write Immutable classes which are critical for designing
thread-safe multi-threading system and reducing amount of synchronization. I
would suggest to see What
is final in Java for more information about final keyword.
Now let's see What is finally in Java? As I said finally is used
for exception handling along with try and catch. As per
Java programming language’s rule, for exception handling you at least need
either catch or finally block. finally block has
special advantage over catch that its guaranteed to be executed despite
whether Exception is thrown or not, this makes it, an ideal place to close
system resource e.g. InputStream
or OutputStream, which is required to release scarce file
descriptor. Closing streams, network connection, database connection in finally
block is good coding practice in Java. By the way from Java 7 you can use try
with resource block to close resource automatically. Since finally is
guaranteed to be executed on most cases, it also gives birth to some tricky Java questions where finally doesn't execute e.g. returning value from
finally block, calling System.exit from try block etc. finally block
always execute, except in case of JVM dies i.e. calling System.exit() . Again
finally is not related to final or finalize in any
way.
Now let’s see What is finalize() method, finalize() is called
by Garbage collection thread just before collecting eligible Objects. This is
the last chance for object to perform any cleanup but since its not guaranteed
that whether finalize() will be called, its bad practice to keep resource till
finalize call. Though you can build a safety net on finalize by double
checking scarce resources. See 10
points on finalize method to know more about specific points of finalize().
So, final, finally and finalize all are
different keyword, they are used for different purpose. only similarity between
them is that they are a Java programming language keyword, other than that final, finalize and finally are
completely different than each other.
Other Java programming interview questions from Javarevisited :
Source:http://javarevisited.blogspot.com/2012/11/difference-between-final-finally-and-finalize-java.html
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