final, static, this, super

Thursday. October 25, 2018 - 1 min

final

• final applies on variable, method and class
  • if the variable is primitive type, cannot change the value.
  • if the variable is a pointer, cannot point it to another object, but internal state of the object can be modified.
  • when final applies on a class, this class cannot be inherited. All method in a final class will be final method.
  • A final method cannot be overriden by subclasses.

static

• static applies to block, variable, method and nested class
• When a member is declared as static, it can be accessed without an instance.
• static block
  • Code inside static block is for initialization of a class(before constructor), and it is only executed one.
• static method
  • static method is part of the class itself, not belonging to any instance of the class.
  • cannot call non static method in the same class directly.
  • can only access static data
  • cannot refer to this or super
  • called by Class.method()
• static variable
  • shared by all instances of this class
  • part of the class not part of any instance
  • called by Class.vari
• why we use pulic static void main()
  • we need a start handler for our project, cause it is not possible to instanciate all classes.

this

• this refers to the current instance
  • this.variable
  • this.method()
• this is optional
  • this makes code readable

super

• super refers to variable and method in parent class
  • super.variable
  • super.method()