chapter_12_beginning_javabook

thisday thismonth thisyear dateprintformat

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Unformatted text preview: ass. 12.1 Base classes and derived classes 389 Date The inheritance mechanism makes all these members available in the lower classes. (Note again that these balloons do not belong to the actual class diagram.) this_day this_month this_year date_print_format is_last_day_of_month() this_is_a_leap_year() is_within_dates() index_for_day_of_week() get_day_of_week() increment() decrement() get_distance_to() get_week_number() is_equal_to() is_not_equal_to() is_earlier_than() is_later_than() toString() This kind of arrow denotes inheritance between classes. The arrow points to the base class (superclass) that is inherited. BetterDate CurrentDate to_string_with_month_name() to_american_format_string() This means that class BetterDate differs from class Date in that it has two additional methods. Class BetterDate has all those fields and methods that are in class Date, and in addition it has these two extra methods. When these sections are empty, it means that class CurrentDate has exactly the same members as its base class Date. These two classes differ in that their constructors are different. Constructors are not always shown in these kinds of class diagrams because it is well known that classes often have constructors. These diagrams do not attempt to describe classes perfectly. The purpose is to give a general overview of the class structure. These are not official UML diagrams Figure 12-1. Class diagram that describes relationships between three classes. 390 Chapter 12: Inheritance and class hierarchies Here, class CurrentDate inherits class Date. The methods of class Date are available methods for the objects of class CurrentDate. // CurrentDate differs from its superclass Date only in that its constructors are different. The first constructor assumes the American date print format. The first constructor creates an object of the standard Java class GregorianCalendar from which it can read the date information that is maintained by the operating system of the computer. After these assignment statements have been executed, this CurrentDate object contains the date of the computer. Calendar and GregorianCalendar are standard Java classes for handling information related to dates and time in Java programs. These classes will be discussed in a later chapter. CurrentDate.java (c) Kari Laitinen import import java.util.Calendar ; java.util.Gre...
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This document was uploaded on 01/20/2014.

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