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Double class
subject			fact

Double class	is a subtopic of The Basics of Java
	is an instance of Java wrapper class
	see also double
Java wrapper class	contains the methods parseInt, toHexString, isDigit
	contains useful class methods
	corresponds to Java primitive data type
	has purpose to allow you to do something with primitive values beyond what the basic operators can accomplish
Java class	can extend only one superclass
	can have more than one constructor each of which has different sets of arguments
	can have the same name as another class if the two classes are not in the same package and their packages are never imported into the same file
	can implement more than one interface
	has form class classname { // declarations of variables // declarations of constructors (discussed below) // declarations of other methods with public ones first }
	is abstract if it has one or more abstract methods
	is stored in a file of the same name
	may implement particular low-level subsystems
	should be placed in its own source file
	should have a unique name since somebody in the future might want to import the packages containing both classes and hence create a name clash
	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
	uses an implements clause to declare that it contains methods for each of the operations specified by the interface
class	declares a list of variables, called instance variables, corresponding to data that will be present in each instance
	has part class name
	has part class variable
	has part code
	has part constructor
	has part instance variable
	has part method
	has part variables
	is divided up into methods
	is drawn as a box with the name of the class inside in a UML class diagram
	is needed in a domain model if you have to store or manipulate instances of it in order to implement a requirement
	represents several similar objects
	should be created to hold a responsibility if the responsibility cannot be attributed to any of the existing classes
	should be named after things their instances represent in the real world
	should not be named after the internals of a computer system such as 'Record', 'Table', 'Data', 'Structure', or 'Information'
data abstraction	groups the pieces of data that describe some entity, so that programmers can manipulate that data as a unit
	helps a programmer to cope with the complexity of data
	hides the details of data
module	has high cohesion if related aspects of a system are kept together in this module, and unrelated aspects are kept out
	lacks side effects if it does not modify any data, and does not leave behind any information, other than its result, that would have an effect on other computations
component	may perform a special-purpose function such as the user interface for a particular system

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