Oops

1. What is Inheritance?

A:  Inheritance: When class want to aquaired the properties of another class we use

the concept of Inheritance.

2.  What is the use of Virtual Keyword for a class?

A:  virtual: This keyword Defines a class or method that allows extension and overrides.

You can’t override a method with the override keyword unless the class or method has

 been defined as virtual.

(Or)

If you define any class as Virtual it can be Inherited by another class.
Example:
public virtual class MyException extends Exception {
// Exception class member
// variable
public Double d;
// Exception class constructor
MyException(Double d) {
this.d = d;
}
// Exception class method
protected void doIt() {}
}

3.What is the use of extends keyword?

A. extends: Defines a class that extents another class.

(or)

If a class want to Inherit another class we use extends keyword.
Example:
public class MyClass1 extends MyClass {
}

4. What is Constructor?

A. Constructor: It is a method with the same name of the class which is used to

 initialize the data members of the class.

Constructor will not have any return type. Constructor will be invoked once at

the time of creating an object

Ex: public Class ClassName{

public ClassName(){

}

}

5. How is Constructor Overloading?

A. Constructor Overloading: With in the same class if you write more than one

constructor with a different no.of  parameters, diff type of parameters we

called it as “Constructor Overloading”.

Ex: public class Example{

Public String name;

Public Integer age;

Public Example(){

name=’---***---‘;

age=20;

}

Public Example(String name){

This.name=name;     }

Public Example(Integer age){

This.age=age;

}

}

6. What is the difference between static and non-static variable?

A. Static And Non-Static: If you define any variable as Static memory will be

allocated only once i.e., on the name of class

Memory for the Non=Static variables will be allocated no.of times based on

 objects that we have created.

Static variables are referred  using  Class name. Memory for the static variables

 will be allocated before the execution   starts

Example:

   Public Class Example{

   Public Static Integer a=0;

   Public  Integer b=0;

   Public void add(){

         a=a+10;

         b=b+10;

          }

         }

7.What are final variables?

A.Final Variables: If you define any variable as final we cant change the value

after the creation  of object. Values for the final variable can be assigned at

 the

time of creating a variable or with in the constructor.

   Every Object can have its own final value.

         Ex:  public class Example{

               Public Integer a;

               Public final Integer b;

               Public final Integer c=10;

               Public Example(Integer  b){

               a= 20;

               this.b= b;

                             }

                        }

                        Debug Log: Example e1=new Example(25);

                            Example e2=new Example(50);

               e1.b=90; // this may give error

                          e1.a=100;