OOPs Interview Question And Answer

Q.1- What is OOPs ?
Ans.- OOps(Object Oriented Programming System) is a Methodology to design a Program using class and Object is known as a OOps.
Q.2- What is Concepts of OOps ?
Ans.- There are following Concepts.

1.   Object.
2.   Class.
3.   Inheritance.
4.   Polymorphism.
5.   Encapsulation.
6.   Abstraction.

Q. 3- What is Object?
Ans.- Any Entity that has state and behavior is Called object. it can be Physical and Logical.
Q. 4- What is Class?
 Ans.- Class is Collection of object is Called Class. it is Logical Entity.
Q.5- What is Inheritance ?
Ans.- When one object Acquires all the Properties and behaviors of parent object is Called Inheritance. It provides code re-usability. it is used to achieve run-time Polymorphism.
Q.6- What is Polymorphism?
Ans.- When one Task is Performed to different way is known as a Polymorphism. in java, we  use Method Overloading and Overriding to achieve Polymorphism.
Q.7- What is Encapsulation?
Ans.-Encapsulation is the process of binding or wrapping code and data together into a single unit is Called Encapsulation. java beans is the fully of encapsulation class because all data members are private here.
Q.8- What is Abstraction?
Ans.- Abstraction is the process of Hiding internal details and showing functionality is Called Abstraction.
In java, we use abstract class and interface to achieve abstraction.
Example- Phone Call.
Q.9- Is the code compiles ? If yes then what will be the output ?

class testDemo { public Integer number(int n) { System.out.println("Integer"); return n; } protected Integer number(Integer n) { System.out.println("int"); return n; } protected Object number(Object n){ System.out.println("Object"); return n;} public static void main(String[] args) { testDemo n12 = new testDemo(); n12.number(10); n12.number("o"); int a[]={10,20,30,05}; int b; b=a.length; System.out.println(b); } }
Ans.-                         Integer
                                 Object
                                  4
Q.10- Is the code compiles ? If yes then what will be the output ?
1. class is over.java
class over { protected int add(int a){ System.out.println("add"); return a; } }
2. class is overTest.java
class overTest extends over{ public Integer add(Integer a){ System.out.print("add1"); return a; } public static void main(String[] args) { overTest o=new overTest(); o.add(11); } }
Ans.-       add.
Q.11- Is the code compiles ? If yes then what will be the output ?
1. class is over.java
interface A { void a(); void b(); void c(); void d(); } abstract class B implements A{ public void c(){ System.out.println("I am c"); } } class M extends B{ public void a() { System.out.println("I am A"); } public void b() { System.out.println("I am B"); } public void d() { System.out.println("I am D"); } } class testMain{ public static void main(String[] args) { A a1=new M(); a1.a(); a1.b(); a1.c(); a1.d(); } }
Ans.-      I am A
              I am B
              I am c
              I am D.
Q.12- Is the code compiles ? If yes then what will be the output ?
class Test{ public static void main(String[] args) { int a=100, b=200; while(++a<--b); System.out.println(+a); System.out.println(+b); } }
Ans.-                     150
                             150