To override a superclass method in a subclass, the subclass method
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You can override any method of a parent class by generating necessary code from a predefined template. PyCharm creates a stub that contains a call to the method of the superclass, leaving the developer with the task of providing some meaningful source code in the method's body. On the menu, click Ctrl+O. Alternatively, you can right-click anywhere in the class file, then click Generate
Alt+Insert, and select Override methods. Select the methods to override (hold the
Shift or Ctrl key to perform a multiple select). The list does not include the methods that are already overridden or cannot be accessed from the current subclass. Click OK and provide the source code for the method body. Hover over the Last modified: 21 July 2022 In the previous chapter, we talked about superclasses and subclasses. If a class inherits a method from its superclass, then there is a chance to override the method provided that it is not marked final. The benefit of overriding is: ability to define a behavior that's specific to the subclass type, which means a subclass can implement a parent class method based on its requirement. In object-oriented terms, overriding means to override the functionality of an existing method. ExampleLet us look at an example. class Animal { public void move() { System.out.println("Animals can move"); } } class Dog extends Animal { public void move() { System.out.println("Dogs can walk and run"); } } public class TestDog { public static void main(String args[]) { Animal a = new Animal(); // Animal reference and object Animal b = new Dog(); // Animal reference but Dog object a.move(); // runs the method in Animal class b.move(); // runs the method in Dog class } }This will produce the following result − OutputAnimals can move Dogs can walk and runIn the above example, you can see that even though b is a type of Animal it runs the move method in the Dog class. The reason for this is: In compile time, the check is made on the reference type. However, in the runtime, JVM figures out the object type and would run the method that belongs to that particular object. Therefore, in the above example, the program will compile properly since Animal class has the method move. Then, at the runtime, it runs the method specific for that object. Consider the following example − Exampleclass Animal { public void move() { System.out.println("Animals can move"); } } class Dog extends Animal { public void move() { System.out.println("Dogs can walk and run"); } public void bark() { System.out.println("Dogs can bark"); } } public class TestDog { public static void main(String args[]) { Animal a = new Animal(); // Animal reference and object Animal b = new Dog(); // Animal reference but Dog object a.move(); // runs the method in Animal class b.move(); // runs the method in Dog class b.bark(); } }This will produce the following result − OutputTestDog.java:26: error: cannot find symbol b.bark(); ^ symbol: method bark() location: variable b of type Animal 1 errorThis program will throw a compile time error since b's reference type Animal doesn't have a method by the name of bark. Rules for Method Overriding
Using the super KeywordWhen invoking a superclass version of an overridden method the super keyword is used. Exampleclass Animal { public void move() { System.out.println("Animals can move"); } } class Dog extends Animal { public void move() { super.move(); // invokes the super class method System.out.println("Dogs can walk and run"); } } public class TestDog { public static void main(String args[]) { Animal b = new Dog(); // Animal reference but Dog object b.move(); // runs the method in Dog class } }This will produce the following result − OutputAnimals can move Dogs can walk and runCan a superclass override a subclass?A subclass cannot override methods that are declared static in the superclass. In other words, a subclass cannot override a class method.
Which methods must be override in the subclass?Subclass must override methods that are declared abstract in the superclass, or the subclass itself must be abstract. Writing Abstract Classes and Methods discusses abstract classes and methods in detail.
Should a subclass override all methods from the superclass?It depends on the type of Superclass, if it's an Abstract class you must override all your method. For concrete class, you only have to override what is required. And this is the fundamental of OOPs that your superclass's methods can be used by subclass.
Under what circumstances would a subclass need to override 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.
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