* The Author class model a book's author. A toString() method that returns " name ( gender) at email", e.g., " Tan Ah Teck (m) at Author Class ( Author.java).(There are no setters for name and gender, as these properties are not designed to be changed.) Public getters/setters: getName(), getEmail(), setEmail(), and getGender().(There is no default constructor, as there is no default value for name, email and gender.) A constructor to initialize the name, email and gender with the given values.Three private member variables: name ( String), email ( String), and gender ( char of either 'm' or 'f' - you might also use a boolean variable called isMale having value of true or false).1: The Author and Book Classes Let's start with the Author classĪ class called Author is designed as shown in the class diagram. We shall begin with reusing classes via composition - through examples. With inheritance, you derive a new class based on an existing class, with modifications or extensions. With composition (aka aggregation), you define a new class, which is composed of existing classes. #POLYMORPHISM JAVA CODE#You can step through this code using the Java Visulaizer by clicking on the following link: Base Example.There are two ways to reuse existing classes, namely, composition and inheritance. The call to methodTwo in thodOne is to thodTwo which is the method from the Derived class.Finally the program returns to methodOne in the Derived class are prints "C". Then the "D" in the Derive methodTwo is printed. Polymorphism is subclassing a class the same parent has different children that all inherit properties from the parent but override them. methodTwo in the Derived class is executed which then calls thodTwo which invokes printin "B" from methodTwo in the Base class. After the call to methodOne in the super class printing "A", the code continues with the implicit thodTwo which resolves from the current object's class which is Derived.So all methods are looked for starting with the Derived class. That is, when a single entity behaves differently in different cases, it is. But the object is really a Derived object. Polymorphism is a concept by which we can perform a single task in different ways. This would be true if the object was created of type Base using new Base.Even though b is declared as type Base it is created as an object of the Derived class, so all methods to it will be resolved starting with the Derived class.If not, the parent of that class will be checked and so on until the method is found. If the method is found there it will be executed. This allows for the benefits of simplified syntax and reduced cognitive overload for developers. Polymorphism allows a child class to share the information and behavior of its parent class while also incorporating its own functionality. When a method is called at run-time the first place that is checked for that method is the class that created the object. Java incorporates the object-oriented programming principle of polymorphism. Remember that an object keeps a reference to the class that created it (an object of the class called Class). At run-time the actual method that is called depends on the actual type of the object. The code won’t compile if the methods don’t exist in that class or some parent class of that class. It is a combination of 2 Greek words: poly and morph. One of the most important features of object-oriented programming (OOPs) is Polymorphism. It is the ability of an object or method to take many forms according to requirements. But, you can only call methods that are available in the Object class unless you cast it back to the String class.Īt compile time the compiler uses the declared type to check that the methods you are trying to use are available to an object of that type. Polymorphism in Java is a concept which enables you to do a single action in various ways. The class String inherits from the class Object so an Object variable can hold a reference to a String object. 11.23 Code Practice with Object Oriented ConceptsĪny object variable can refer to an object of the declared type or any descendant (subclass) of the declared type at run-time.11.10 Access to Inherited Private Fields.11.9 Using Super to call an Overridden Method.11.1 Object-Oriented Programming Concepts.
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