Java Questions

Use Interfaces when…

- You see that something in your design will change frequently.

- If various implementations only share method signatures then it is better to use Interfaces.

- You need some classes to use some methods which you don't want to be included in the class, then you go for the interface, which makes it easy to just implement and make use of the methods defined in the interface.

Use Abstract Class when…

- If various implementations are of the same kind and use common behavior or status then abstract class is better to use.

- When you want to provide a generalized form of abstraction and leave the implementation task with the inheriting subclass.

- Abstract classes are an excellent way to create planned inheritance hierarchies. They're also a good choice for nonleaf classes in class hierarchies.

yes if the method is ovreriding method

no if the method is not overriding method

By using overloading we can add new functionality to the sub class.

Autoboxing is the process of converting a primitive type data into its corresponding wrapper class object instance.

Example:

Integer number = new Integer (100); // number is now refers to the object 100

Unboxing is the process of converting a wrapper instance into a primitive type.

Example: 

Integer number = new Integer (100); 

int num = number;// without type casting number would be changed into int type

Constructor is not a special method.

Constructor is block of code that is executed automatically whenever object of the class is created.

Interface data is static data why bcoz interface supports multiple inheritance.

if inteface data is non-static then there is chance for replication of the data (bcoz of replication of data ambiguity problem occurs )

Yes, we can. In order to compile a java program, we don't require any main method. But to execute a java program we must have a main in it (unless it is an applet or servlet). Because main is the starting point of a java program.

Top level class is also called outer class. It is not defined inside any class.

Ex:

class A {  //top level class

}