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Constructor methods The statement: new TextItem( "Deitel & Deitel", 1041, "Dei 304.167");might result in the following object being created in the computer's memory:
Notice that the onLoan status is false and the value of daysLate is zero, even thought these values were not part of the statement. In fact, even though values like "Deitel & Deitel" were part of the statement, how did they get into an object? Statements that create objects are actually invoking methods called constructor methods. Each class has a constructor method that executes when a new object is to be created of that class. We might define a constructor method for our TextItem class as follows: void TextItem( String itemTitle,int itemNumPages, As can be seen, for this constructor the arguments to the method (title, number of pages and shelf mark) are used to initialise some of this new object's variables. In addition, some variables (onLoan and daysLate) are automatically initialised to values appropriate for a new object of the class.// use method arguments to initialise variables} A method is recognized as a constructor by having the same identifier (name) as the class, e.g. TextItem. All classes have constructor methods that state what should be done to create a new object of the class. Sometimes constructors are not explicit in the definition of the class (they may be inherited from another class ?we'll look more at inheritance in the next unit). Constructors do not have to have arguments ?for some classes of objects there is some reasonable way create an object that does not need to have any initial values provided.
RITSEC - Global Campus
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