![]() ![]() So yes, you can create an abstract class constructor in Java when you need to. Before diving into when to use an abstract class, let’s look at their most relevant characteristics: We define an abstract class with the abstract modifier preceding the class keyword. The Java spec only specifies that the anonymous class, which is the offspring of the (optionally) abstract class or implementation of an interface, can not have a constructor by her own right. However, since you have a list of AClass, you do not need to know the exact subtype: an abstract function that make a copy would be sufficient. In this tutorial, we’ll learn the basics of abstract classes in Java, and in what cases they can be helpful. You can have a constructor in the abstract class that accepts the init parameters. The only difference is that you can’t instantiate an abstract class, so you need to extend it and call the constructor using super(). I cannot create a copy constructor in AClass because it is an abstract class and I cannot know the name of the class which will inherit by AClass. However, be aware that a class can extend only one. The variables don’t have to be final variables, but if your abstract class has one or more variables, and you want them to be initialized on instantiation, then you need to create the constructor.įinally, an abstract class constructor behaves just like any other class type. Use an abstract class instead of a trait when the base functionality must take constructor parameters. but, as constructors are often substituted by factorymethods anyway, you could implement abstract. There is one condition when you might want to define a constructor in an abstract class, and that is when you want to enforce that all subclasses of the superclass have specific member variables initialized. Solved-Java abstract class, abstract constructor-Java. The only way to guarantee that a superclass constructor is called is to have only one constructor in the superclass. The variable is initialized when an instance of the subclass is created and then can’t be changed. The subclass has to call either one (or both, if you redefine both as in your example) of the superclass constructors but you cannot force it to redefine constructors with the same signatures of the superclass. ![]() ![]() Class Terrier extends Dog īy creating an abstract class that has a constructor, you ensure that its subclasses will have the final variable initialized. ![]()
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