• finalize

Garbage collection and finalize

• Java performs garbage collection for you and eliminates the need to free objects explicitly.
• This eliminates a common cause of errors in C/C++ and other languages (memory leaks). Never have to worry about dangling references.
• When an object is no longer reachable the space it occupies can be reclaimed.
• Space is reclaimed at the garbage collector's discretion.
• Creating and collecting large numbers of objects can interfere with time-critical applications.

finalize

• A class can implement a finalize method.
• This method will be executed before an object's space is reclaimed.
• Gives you a chance to use the state of the object to reclaim other non-Java resources.
• finalize is declared like this:

      protected void finalize() throws Throwable {
         // ...
      }
  

• Important when dealing with non-Java resources, such as open files.
• Example: a class that opens a file should provide a close() method. Even then, there is no guarantee that the programmer will call the close() method, so it should be done in a finalize method.

      public void close()
      {
         if (file != null)
         {
            file.close();
            file = null;
         }
      }
      protected void finalize() throws Throwable
      {
         try
         {
            close();
         } 
         finally
         {
            super.finalize();
         }
      }
  

• The close method is written carefully in case it is called more than once.
• super.finalize is called to make sure your superclass is also finalized.
• Train yourself to always do this.