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abstract class
subject			fact

abstract class	can define 1 programming interface
	can have concrete methods or instance variables
	can omit some or all of the implementation of its methods
	can provide 0 or more method declarations for all methods needed to implement its programming interface to its subclasses
	cannot be final
	cannot have instances
	defines generic behaviour
	has definition A class that can only be subclassed - it cannot be instantiated or the compiler will display an error message and refuse to compile the program
	has purpose to hold features that will be inherited by two or more subclasses
	is the opposite of concrete class
	is a subtopic of Classes
	is created by specifying the abstract keyword on the first line when you declare the class
	is not required to have any abstract methods
	is a kind of class
	usually is not fully defined
class	a class is a member of the default package unless its source file contains a package statement
	if a class has one or more abstract methods or the class does not implement all of its superclass's abstract methods then the class must be declared abstract
	if a class has no explicit constructor then the default constructor is used
	if a class implements an interface then the class must provide implementations for all methods declared in the interface and its superinterfaces or the class must be declared abstract
	if a class is not declared public then it is accessible only to members of the same package
	adds 0 or more variables to the variables it inherits from its superclass
	adds 0 or more methods to the methods it inherits from its superclass
	can access any public class in other packages
	can be imported from a package
	can extend only one superclass
	can implement more than one interface
	can override methods that are inherited from the class's superclass
	can protect its members from access by other classes or objects using an access modifier
	cannot inherit method implementations from an interface
	contains all of the code that relates to its objects including code describing how the objects of the class are structured - i.e. the data stored in each object that implement the properties the procedures, called methods, that implement the behaviour of the objects
	contains data associated with each object
	declares a list of variables, called instance variables, corresponding to data that will be present in each instance
	has benefit reusability modularity
	has example public class HelloWorld { public static void main(String[] args) { System.out.println("Hello World!"); } }
	has part class name
	has part code
	has part constructor
	has syntax class classname { // declarations of variables // declarations of constructors // declarations of other methods with public ones first }
	inherits 0 or more methods from its superclass
	inherits 0 or more variables from its superclass
	inherits behaviour from its superclass
	is a descendant of Object class
	is specified by 1 class definition
	may have access modifier public or private or protected
	represents several similar objects
	should be a member of 1 named package rather than the default package
	should be named after a thing its instances represent in the real world
	should be placed in its own source file
	should not be named after the internals of a computer system such as 'Record', 'Table', 'Data', 'Structure', or 'Information'
	should order elements as follows: class variables instance variables constructors the most important public methods methods that are simply used to access variables private methods
	to instantiate you create an instance of it
	uses an implements clause to declare that it contains methods for each of the operations specified by the interface
access unit	has access mode
syntactic unit	has syntax rule bold = mandatory italic = non-terminal normal font = optional

Kinds of abstract class :

• Number class (3 facts)

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