When invoking a superclass version of an overridden method the super keyword is used. The overriding method can throw narrower or fewer exceptions than the overridden method. However, the overriding method should not throw checked exceptions that are new or broader than the ones declared by the overridden method. If a method cannot be inherited, then it cannot be overridden.Ī subclass within the same package as the instance's superclass can override any superclass method that is not declared private or final.Ī subclass in a different package can only override the non-final methods declared public or protected.Īn overriding method can throw any uncheck exceptions, regardless of whether the overridden method throws exceptions or not. Instance methods can be overridden only if they are inherited by the subclass.Ī method declared final cannot be overridden.Ī method declared static cannot be overridden but can be re-declared. For example: If the superclass method is declared public then the overridding method in the sub class cannot be either private or protected. The access level cannot be more restrictive than the overridden method's access level. The return type should be the same or a subtype of the return type declared in the original overridden method in the superclass. The main method in this class creates an instance of Cat and invokes testClassMethod() on the class and testInstanceMethod() on the instance. The argument list should be exactly the same as that of the overridden method. The Cat class overrides the instance method in Animal and hides the static method in Animal. Why use methods To reuse code: define the code once, and use it many times. Methods are used to perform certain actions, and they are also known as functions. You can pass data, known as parameters, into a method. This program will throw a compile time error since b's reference type Animal doesn't have a method by the name of bark. Java Methods Previous Next A method is a block of code which only runs when it is called. TestDog.java:26: error: cannot find symbol Being a virtual machine means the JVM is an abstraction of an underlying, actual machinesuch as. Then, at the runtime, it runs the method specific for that object. The JVM is a virtual machine that runs Java class files in a portable way. Therefore, in the above example, the program will compile properly since Animal class has the method move. However, in the runtime, JVM figures out the object type and would run the method that belongs to that particular object. The benefit of overriding is: ability to define a behavior thats specific to the subclass type, which means a subclass can. 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 reason for this is: In compile time, the check is made on the reference type. In the previous chapter, we talked about superclasses and subclasses. In the above example, you can see that even though b is a type of Animal it runs the move method in the Dog class. This will produce the following result − Output ("Dogs can walk and run") Īnimal a = new Animal() // Animal reference and objectĪnimal b = new Dog() // Animal reference but Dog objectĪ.move() // runs the method in Animal classī.move() // runs the method in Dog class
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