I was having an issue with a subclass's method getting called that overrode a method, so I created a small app to test it. When the superclass calls a method that its subclass overrides, the superclass's version of the method still gets called instead of the subclass's version, which overrides the superclass's method and should be the method getting called. Show
Expected output: Actual output: Superclass:
Subclass:
asked Aug 19, 2015 at 21:28
Adam EvansAdam Evans 2,05221 silver badges28 bronze badges 3 Make sure that the object's class is answered Aug 19, 2015 at 22:20
1 It's also worth checking that you're not trying to override in an extension. For some reason the override can't be done in an extension. answered Mar 9, 2016 at 20:37
MikeCocoaMikeCocoa 3062 silver badges7 bronze badges 1 I just stumbled into this issue in Xcode 8.1 / Swift 3.0 I created a super class with a method stub with the intention of overriding it in my subclass, but calling it from the super and to my surprise the override wasn't being called. My solution to the problem was to create a protocol. Using the OP's example, my solution looks like this: Super:
Subclass:
Protocol:
Protocol extension:
answered Nov 12, 2016 at 1:22
0 In any object-oriented programming language, Overriding is a feature that allows a subclass or child class to provide a specific implementation of a method that is already provided by one of its super-classes or parent classes. When a method in a subclass has the same name, same parameters or signature, and same return type(or sub-type) as a method in its super-class, then the method in the subclass is said to override the method in the super-class. Nội dung chính
Method overriding is one of the way by which java achieve Run Time Polymorphism.The version of a method that is executed will be determined by the object that is used to invoke it. If an object of a parent class is used to invoke the method, then the version in the parent class will be executed, but if an object of the subclass is used to invoke the method, then the version in the child class will be executed. In other words, it is the type of the object being referred to (not the type of the reference variable) that determines which version of an overridden method will be executed. class Parent { void show() { System.out.println("Parent's show()"); } } class Child extends Parent { @Override void show() { System.out.println("Child's show()"); } } class Main { public static void main(String[] args) { Parent obj1 = new Parent(); obj1.show(); Parent obj2 = new Child(); obj2.show(); } } Output: Parent's show() Child's show() Rules for method overriding:
Note :
Why Method Overriding ? As stated earlier, overridden methods allow Java to support run-time polymorphism. Polymorphism is essential to object-oriented programming for one reason: it allows a general class to specify methods that will be common to all of its derivatives while allowing subclasses to define the specific implementation of some or all of those methods. Overridden methods are another way that Java implements the “one interface, multiple methods” aspect of polymorphism. Dynamic Method Dispatch is one of the most powerful mechanisms that object-oriented design brings to bear on code reuse and robustness. The ability to exist code libraries to call methods on instances of new classes without recompiling while maintaining a clean abstract interface is a profoundly powerful tool. Overridden methods allow us to call methods of any of the derived classes without even knowing the type of derived class object. When to apply Method Overriding ?(with example) Overriding and Inheritance : Part of the key to successfully applying polymorphism is understanding that the superclasses and subclasses form a hierarchy which moves from lesser to greater specialization. Used correctly, the superclass provides all elements that a subclass can use directly. It also defines those methods that the derived class must implement on its own. This allows the subclass the flexibility to define its methods, yet still enforces a consistent interface. Thus, by combining inheritance with overridden methods, a superclass can define the general form of the methods that will be used by all of its subclasses. Let’s look at a more practical example that uses method overriding. Consider an employee management software for an organization, let the code has a simple base class Employee, the class has methods like raiseSalary(), transfer(), promote(), .. etc. Different types of employees like Manager, Engineer, ..etc may have their implementations of the methods present in base class Employee. In our complete software, we just need to pass a list of employees everywhere and call appropriate methods without even knowing the type of employee. For example, we can easily raise the salary of all employees by iterating through the list of employees. Every type of employee may have its logic in its class, we don’t need to worry because if raiseSalary() is present for a specific employee type, only that method would be called. class Employee { public static int base = 10000; int salary() { return base; } } class Manager extends Employee { int salary() { return base + 20000; } } class Clerk extends Employee { int salary() { return base + 10000; } } class Main { static void printSalary(Employee e) { System.out.println(e.salary()); } public static void main(String[] args) { Employee obj1 = new Manager(); System.out.print("Manager's salary : "); printSalary(obj1); Employee obj2 = new Clerk(); System.out.print("Clerk's salary : "); printSalary(obj2); } } Output: Manager's salary : 30000 Clerk's salary : 20000 Related Article:
This article is contributed by Twinkle Tyagi and Gaurav Miglani. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to . See your article appearing on the GeeksforGeeks main page and help other Geeks. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above. When a method is overridden in a subclass?The ability of a subclass to override a method allows a class to inherit from a superclass whose behavior is "close enough" and then to modify behavior as needed. The overriding method has the same name, number and type of parameters, and return type as the method that it overrides. What does it mean when a method is overridden?In Java, method overriding occurs when a subclass (child class) has the same method as the parent class. In other words, method overriding occurs when a subclass provides a particular implementation of a method declared by one of its parent classes. When a superclass method is overridden in a subclass The subclass version of may invoke the superclass version of a portion of the work?When a superclass method is overridden in a subclass, the subclass version often calls the superclass version to do a portion of the work. Failure to prefix the superclass method name with the keyword super and a dot (.) How a superclass method is overridden in a subclass?A subclass within the same package as the instance's superclass can override any superclass method that is not declared private or final. A subclass in a different package can only override the non-final methods declared public or protected. When a subclass overrides a superclass method?When a method in a subclass has the same name, same parameters or signature, and same return type(or sub-type) as a method in its super-class, then the method in the subclass is said to override the method in the super-class. Method overriding is one of the way by which java achieve Run Time Polymorphism.
When a subclass method has the same name as a superclass method the subclass method overrides the superclass method?If a method in a subclass has the same signature as a method in the superclass, the subclass method overloads the superclass method. If two methods in the same class have the same name but different signatures, the second overrides the first.
How do you invoke an overridden superclass method from the subclass?The overridden method shall not be accessible from outside of the classes at all. But you can call it within the child class itself. to call a super class method from within a sub class you can use the super keyword.
Can a subclass call a superclass method?Subclass methods can call superclass methods if both methods have the same name. From the subclass, reference the method name and superclass name with the @ symbol.
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