@Deprecated

 @Deprecated  

• Used in managed packages
• Any classes,methods, interfaces, exceptions,variables or enums ,etc which can no longer be referenced in subsequent releases (of that Managed Package).
• Mostly used when you are refactoring / making more changes/improvements in your Managed Package as the requirements evolve.
• It restricts new subscribers to see "deprecated" elements while existing subscribers/API integrations  get proper functioning elements as they were.
• All 'global' modifiers need to be 'deprecated' as who referred your 'decprecated' element.
• Unmanaged packages cannot contain code that uses the deprecated keyword.
• Can't use with WebSerivces
• Enum, Interface, Abstract classes need to depcrecated totally - cant decpracate individual method or individual enum value.

 EXAMPLE : 

       
            // This method is deprecated. Use myOptimizedMethod(String a, String b) instead.

  @deprecated 
  global void myMethod(String a) { 

 }