Static

• DO NOT belong to any instance, but belongs to the class

• when to use ?

  • If only one instance of static member needed
  • needs to be shared across all the classes

• Applications

  • Variables

    • value are independent of the object
    • values are supposed to be shared across the objects/instances
    • can be accessed from both class/object

  • Methods

    • to access/manipulate static variables and other static methods that don’t depend upon objects.
    • static methods are widely used in utility and helper classes.
    • cannot be overridden
    • can’t use this or super keywords

  • Blocks

    • can have multiple static blocks and are resolved in the order of existence

  • Nested class

    • Generally used for Singleton class

    • public class Singleton  {
        private Singleton() {}
      
        private static class SingletonHolder {
          public static final Singleton instance = new Singleton();
        }
      
        public static Singleton getInstance() {
          return SingletonHolder.instance;
        }
      }

    • No Synchronization required

    • static nested classes can access all static members of the enclosing class, including private ones.

    • Java programming specification doesn’t allow us to declare the top-level class as static