Final Variables – Object-Oriented Programming
Final Variables A final variable is a variable whose value cannot be changed during its lifetime once it has been initialized. A final variable is declared with the keyword final in its declaration. Any attempt to reassign a value will result in a compile-time error. Declaring a variable as final has the following implications: For all paths of execution through the code, the compiler checks that a final variable is assigned only once before it is accessed, and when in doubt, the compiler issues an error (p. 232). A blank final variable is a final variable whose declaration does not specify an initializer expression. A constant variable is a final variable of either a primitive type or type String that is initialized with a constant expression. Constant variables can be used as case labels of a switch statement. We distinguish between two kinds of final variables: final fields that are…
Abstract Methods in Classes – Object-Oriented Programming
Abstract Methods in Classes In this subsection we discuss in more detail declaring and overriding abstract methods in classes. Declaring an abstract Method An abstract method in an abstract class has the following syntax: Click here to view code image access_modifier abstractreturn_type method_name (formal_parameter_list) throws_clause; An abstract method does not have an implementation; that is, no method body is defined for an abstract method, and only the method header is provided in the class declaration. The keyword abstract is mandatory in the header of an abstract method declared in a class. Its class is then incomplete and must be explicitly declared as abstract. Subclasses of an abstract class must then override the abstract method to provide the method implementation; otherwise, they must also be declared as abstract. Overriding an abstract Method When overriding an abstract method from the superclass, the notation @Override should always be used in the overriding method in the subclass.…