home

1). What is Oops?

Ans: Object oriented programming organizes a program

around its data, i.e., objects and a set of well defined interfaces to

that data. An object-oriented program can be characterized as data

controlling a access to code.

2). What is the difference between Procedural and Oops?

Ans: a) In procedural program, programming logic follows

certain procedures and the instructions are executed one after

another. In Oops program, unit of program is object which is nothing

but combination of data and code.

b) In procedural program, data is exposed to the whole program

whereas in Oops program, it is a accessible with in the object and

which in turn assures the security of the code.

3). What are Encapsulation, Inheritance and Polymorphism?

Ans: Encapsulation is the mechanism that binds together code

data it manipulates and keeps both safe from outside interference

and misuse.

Inheritance is the process by which one objects acquire the

properties of another object.

Polymorphism is the feature that allows one interface to be

used for general class action.

4). What is the difference between Assignment and

Initialization?

Ans: Assignment can be done as many times as desired

whereas initialization can be done only once.

5). What are Class, Constructor and Primitive data types?

Ans: Class is a template for multiple objects with similar

features and it is a blue print for objects. It defines a type of objects

according to the data the object can hold and the operations the

object can perform.

Constructor is a special kind of method that determines how an

object is initialized when created.

Primitives data types are 8 types and they are:

Byte, Short, Int, Long, Char

Float, Double

Boolean

6). What is an object and how do you allocate memory to it?

Ans: Object is an instance of a class and it is a software unit

that combines a structured set of data with a set of operations for

inspecting and manipulating that data. When an object created using

new operator, memory is allocated to it.

7). What is the difference between constructor and method?

Ans: Constructor will be automatically invoked when an object

is created whereas method has to be called explicitly.

8). What are methods and how are they defined?

Ans: Methods are functions that operate on instances of

classes in which they are defined. Objects can communicate with

each other using methods and can call methods in other classes.

Method definition has four parts. They are name of the method,

type of object or primitive type the method returns, a lisit of

parameters and the body of the method. A method’s signature is a

combination of the first three parts mentioned above.

9). What is the use of bin and lib in JDK?

Ans: Bin contains all tools such as javac, appletviewer, awt

tool, etc., whereas lib contains API and all packages.

10). What is casting?

Ans: Casting is used to convert the value of one to another.

11). How many ways can an argument be passed to a

subroutine and explain them?

Ans: An argument can be passed in two ways. They are

passing by value and passing by reference.

Passing by value: This method copies the value of an

argument into the formal parameter of the of the subroutine.

Passing by reference: In this method, a reference to an

argument (not the value of the argument) is passed to parameter.

12). What is the difference between an argument and a

parameter?

Ans: While defining method, variables passed in the method

are called parameters. While using those method, values passed to

those variables passed to those variables are called arguments.

13). What are different type of access modifiers?

Ans: Public: Any thing declared as public can accessed from

any where

Private: Any thing declared as private can’t be seen outside of

its class.

Protected: Any thing declared as protected can be accessed

by classes in the same package and subclasses in the other

packages.

Default modifier: Can be accessed only to classes in the same

packages.

14). What is final, finalize() and finally?

Ans: Final: Final keyword can be used for class, method and

variables. A final cannot be subclassed and it prevents other

programmers from subclassing a secure class to invoke insecure

methods.

A final method can’t be overridder

A final variable can’t change from its initialized value.

Finalize(): finalize() method is used just before an object is

destroyed and can called just prior to garbage collection.

Finally: finally, a key word used in exception handling, creates a

block of code that will be executed after a try/catch block has

completed and before the code following try/catch block. The finally

block will execute whether or not an exception is thrown.

For example, if a method opens a file upon exit, then you will

not want the code that closes the file to be bypassed by the

exception-handling mechanism. This finally keyword is designed to

address this contingency.

15). What is UNICODE?

Ans: Unicode is used for internal representation of characters

and strings and it uses 16bits to represent each other.

16). What is Garbage Collection and how to call it explicitly?

Ans: When an object is no longer referred to by any variable,

java automatically reclaims memory used by that object. This is

known as garbage collection.

System.ge() method may ve used to call it explicitly.

17). What is finalize() method?

Ans: finalize() method is used just before an object is

destroyed and can be called just prior to garbage collection.

18). What are Transient and Volatile Modifiers?

Ans: Transient: The transient modifier applies to variables

only and it is not stored as part of its object’s Persistent state.

Transient variables are not serialized.

Volatile: Volatile modifier applies to variables only and it tells

the complier that the variable modified by volatile can be changed

unexpectedly by other parts of the program.

19). What is Method Overloading and Method Overrding?

Ans: Method overloading: When in a class having the same

method name with different arguments is said to be method

overloading.

Method overriding: When a method in a class having the same

method name with same arguments is said to be method overriding.

20). What is difference between overloading and overriding?.

Ans: a). In overloading there is a relationship between

methods available in the same class whereas in overriding, there is

relationship between a super class method and subclass method.

b). Overloading does not block inheritance from the super

class whereas overriding blocks inheritance from the super class.

c) In overloading, separate methods share the same name

whereas in overriding, sub class method replaces the super class.

d) Overloading must have different method signatures whereas

overriding must have same signature.