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Wednesday, July 15, 2009


14.Can overloaded methods be override too?
Yes, derived classes still can override the overloaded methods. Polymorphism can still happen. Compiler will not binding the method calls since it is overloaded, because it might be overridden now or in the future.

15.Is it possible to override the main method?
NO, because main is a static method. A static method can't be overridden in Java.

16.How to invoke a superclass version of an Overridden method?
To invoke a superclass method that has been overridden in a subclass, you must either call the method directly through a superclass instance, or use the super prefix in the subclass itself. From the point of the view of the subclass, the super prefix provides an explicit reference to the superclass' implementation of the method.
// From subclass

17.What is super?
super is a keyword which is used to access the method or member variables from the superclass. If a method hides one of the member variables in its superclass, the method can refer to the hidden variable through the use of the super keyword. In the same way, if a method overrides one of the methods in its superclass, the method can invoke the overridden method through the use of the super keyword.
· You can only go back one level.
· In the constructor, if you use super(), it must be the very first code, and you cannot access any variables or methods to compute its parameters.

18.How do you prevent a method from being overridden?
To prevent a specific method from being overridden in a subclass, use the final modifier on the method declaration, which means "this is the final implementation of this method", the end of its inheritance hierarchy.
public final void exampleMethod() {
// Method statements

19.What is an Interface?
An interface is a description of a set of methods that conforming implementing classes must have.
· You can’t mark an interface as final.
· Interface variables must be static.
· An Interface cannot extend anything but another interfaces.

20.Can we instantiate an interface?
You can’t instantiate an interface directly, but you can instantiate a class that implements an interface.

21.Can we create an object for an interface?
Yes, it is always necessary to create an object implementation for an interface. Interfaces cannot be instantiated in their own right, so you must write a class that implements the interface and fulfill all the methods defined in it.

22.Do interfaces have member variables?
Interfaces may have member variables, but these are implicitly public, static, and final- in other words, interfaces can declare only constants, not instance variables that are available to all implementations and may be used as key references for method arguments for example.

23.What modifiers are allowed for methods in an Interface?
Only public and abstract modifiers are allowed for methods in interfaces.

24.What is a marker interface?
Marker interfaces are those which do not declare any required methods, but signify their compatibility with certain operations. The interface and Cloneable are typical marker interfaces. These do not contain any methods, but classes must implement this interface in order to be serialized and de-serialized.

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