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This is only necessary if a superclass implements a public clone() method, or to prevent a subclass from using this class's clone() method to obtain a copy. Classes don't usually inherit a public clone() method because Object doesn't have a public clone() method, so it is usually unnecessary to explicitly implement a non-functional clone() method.
A disadvantage is that one often cannot access the clone() method on an abstract type. Most interfaces and abstract classes in Java do not specify a public clone() method. Thus, often the only way to use the clone() method is if the class of an object is known, which is contrary to the abstraction principle of using the most generic type possible.
In Java, the Object class contains the clone() method, which copies the object and returns a reference to that copied object. Since it is in the Object class, all classes defined in Java will have a clone method available to the programmer (although to function correctly it needs to be overridden at each level it is used). Cloning an object in ...
To implement the pattern, the client declares an abstract base class that specifies a pure virtual clone() method. Any class that needs a " polymorphic constructor " capability derives itself from the abstract base class, and implements the clone() operation.
The implementation of methods is usually provided in a separate source file, with the following syntax ... Java x.toString() x.clone() [53] x.equals(y) x.compareTo(y ...
This example uses a String as the state, which is an immutable object in Java. In real-life scenarios the state will almost always be a mutable object, in which case a copy of the state must be made. It must be said that the implementation shown has a drawback: it declares an internal class.
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The resulting instance will inherit all the methods and properties that were defined in the class, which acts as a kind of template from which similarly typed objects can be constructed. Systems that support ex nihilo object creation allow new objects to be created from scratch without cloning from an existing prototype. Such systems provide a ...