Variable && Method

Member variable VS Local variable

1. Syntax form

   Member variables belong to classes, while local variables are variables or parameters of methods.

2. Storage method

   Member variable belongs to the class or instance. Objects exist in heap memory, and local variables exist in stack memory.

3. Survival time

   Member variables exist with the creation of objects, while local variables are generated with the call of methods and die with the end of method calls.

4. Default value

   Member variable will be automatically assigned to the default value of the type (Exception: the final member variable must be explicitly assigned), while the local variable will not be automatically assigned.

Static method VS Instance method

1. Call

   Static method can be called byclass.method&&object.method, while Instance method can only be called by the latter. Calling a static method does not require creating an object.

2. Restrictions on Access Class Members

   Static methods only allow access to static members.

Final

• final variable:
  • The value can’t be modified once it has been assigned.
  • If any value has not been assigned to that variable, then it can be assigned only by the constructor of the class.
• final method:
  • Cannot be overridden by its children’s classes.
  • A constructor cannot be marked as final because whenever a class is inherited, the constructors are not inherited. Hence, marking it final doesn’t make sense. Java throws compilation error saying - modifier final not allowed here
• final class:
  • No classes can be inherited from the final class . But that final class can extend other classes for its usage.

Static

• static method and static variable:
  • Belong to the class, not to the object of the class, so they are shared by all instances of the class.
  • Gets memory where the class is loaded during ***compile time.
  • Directly called with the help of class names. E.g. static method: Math.max(), Math.min(). static variable: array.length.
• static class:
  • *Only **inner class and work like other static members of the class.

Static Method Overload Vs Override

• Can be overload: There can be two or more static methods in a class with the same name but differing input parameters.
• Can’t be override: Overriding or dynamic polymorphism occurs during the runtime, but the static methods are loaded and looked up at the compile time statically.