Final keyword - Java

Reference can not be reassigned. But you can change its internals (it is mutable, if it was originally). So this works :
  final A ob = new A();
  ob.setI(6)
but this doesn't :

  final A ob = new A();
  ob = new A();

 ------------------------------------------------------------------------------------------------------------------------

 1. Final keyword can be applied to member variable, local variable, method or class in Java.
2. Final member variable must be initialized at the time of declaration or inside constructor, failure to do so will result in compilation error.

3. You can not reassign value to final variable in Java.

4. Local final variable must be initializing during declaration.

5. Only final variable is accessible inside anonymous class in Java.

6. Final method can not be overridden in Java.

7. Final class can not be inheritable in Java.

8. Final is different than finally keyword which is used on Exception handling in Java.

9. Final should not be confused with finalize() method which is declared in object class and called before an object is garbage collected by JVM.

10. All variable declared inside java interface are implicitly final.

11. Final and abstract are two opposite keyword and a final class can not be abstract in java.

12. Final methods are bonded during compile time also called static binding.

13. Final variables which is not initialized during declaration are called blank final variable and must be initialized on all constructor either explicitly or by calling this(). Failure to do so compiler will complain as "final variable (name) might not be initialized".

14. Making a class, method or variable final in Java helps to improve performance because JVM gets an opportunity to make assumption and optimization.

15. As per Java code convention final variables are treated as constant and written in all Caps e.g.

private final int COUNT=10;

16. Making a collection reference variable final means only reference can not be changed but you can add, remove or change object inside collection. For example:

private final List Loans = new ArrayList();
list.add(“home loan”);  //valid
list.add("personal loan"); //valid
loans = new Vector();  //not valid

That’s all on final in Java. We have seen what final variable, final method is and final class in Java and what does those mean. In Summary whenever possible start using final in java it would result in better and faster code.


Read more: http://javarevisited.blogspot.com/2011/12/final-variable-method-class-java.html#ixzz3ntHAPnsv

Comments

Post a Comment

Popular posts from this blog

EJB - Stateful vs Stateless

For  stateless session beans  the server can maintain a variable amount of instances in a pool. Each time a client requests such a stateless bean (e.g. through a method) a random instance is chosen to serve that request. That means if the client does two subsequent requests it is possible that two different instances of the stateless bean serve the requests. In fact there is no conversational state between the two requests. Also if the client disappears, the stateless bean does not get destroyed and can serve the next request from another client. On the other hand a  stateful session bean  is closely connected to the client. Each instance is created and bounded to a single client and serves only requests from that particular client. So happens that if you do two subsequent requests on a stateful bean, your request will be served always from the same instance of the bean. That means you can maintain a conversational state between the requests. At the end of the li...
Read more

Mirror binay tree - Java

public class TreeNode {     private TreeNode left;     private TreeNode right;     private Object value;     public TreeNode getLeft() {         return left;     }     public TreeNode setLeft(TreeNode left) {         this.left = left;         return this;     }     public TreeNode getRight() {         return right;     }     public TreeNode setRight(TreeNode right) {         this.right = right;         return this;     }     public Object getValue() {         return value;     }     public TreeNode setValue(Object value) {         this.value = value;         return this;     } } public class Mirror {     public stat...
Read more