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Q61. Give an example of how Object Oriented Programming Concepts can be implemented.

Ans. You can implement encapsulation in Java by keeping the fields (class variables) private and providing public getter and setter methods to each of them. Java Beans are examples of fully encapsulated classes. Encapsulation in Java: Restricts direct access to data members (fields) of a class.

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Q62. Explain OOPs

or

Explain OOPs Principles

or

Explain OOPs Concepts

or

Explain OOPs features

or

Tell me something about OOPs

Ans. OOPs or Object Oriented Programming is a Programming model which is organized around Objects instead of processes. Instead of a process calling series of processes, this model stresses on communication between objects. Objects that all self sustained, provide security by encapsulating it's members and providing abstracted interfaces over the functions it performs. OOP's facilitate the following features

1. Inheritance for Code Reuse
2. Abstraction for modularity, maintenance and agility
3. Encapsulation for security and protection
4. Polymorphism for flexibility and interfacing

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Very frequently asked. Usually among very first few questions.

Q63. Define encapsulation in Java ?

Ans. Encapsulation is a feature of OOP's that binds the data and it's associated methods together as a single unit and facilitate protection and data hiding by providing minimal interface to outside. For example - member variables are declared private and are accessed through public methods. Moreover we have private methods that can only be used internally and hence providing minimal interface to outside class through use of public methods.

Sample Code for encapsulation

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Q64. Write a method, that compare two numbers and return the bigger one ?

Ans. int compare(int a, int b) {
a>b? return a: return b;
}

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Q65. What problem we could have with ArrayList which aren't possible with Vectors ?

Ans. ArrayLists aren't synchronized and hence doesn't allow synchronized access. As multiple threads can access an arraylist in parallel, it may result in an inconsistent state.

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Q66. What is the use of final keyword ?

Ans. final keyword is a modifier that means differently when applied to variables, methods and classes.

1. Final variable cannot be changed once initialized
2. Final method cannot be overridden
3. Final class cannot be sub classed

Sample Code for final variable

Sample Code for final method

Sample Code for final class

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Q67. What are the examples of immutable objects in Java ?

Ans. Following Classes in Java SE creates immutable objects

String class
Wrapper Classes like Integer, Float etc.
StackTraceElement
Most Enum classes
File Class
Locale Class

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Q68. Which of following is / are valid static final declaration ?

public static final String MAX_NUM = "10";
public static final Object NULL = null;
public static final MathContext MATH_CONTEXT = new MathContext(2,RoundingMode.CEILING);

Ans. All are valid declarations.

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Q69. What is the difference between reference and object ?

Ans. Object is an entity in Java , i.e which has a state ( instance variables ) and methods attached to it ( static or non static , through class definition ). References are the identifiers that are used to point to objects.

For example -

Employee emp = new Employee();
emp = new Employee();

In this code, emp is the reference that gets assigned to the new object created by the new operator. In the second line , we have assigned the same reference to another object. So with these 2 lines of code, we have 2 objects in memory with reference emp now pointing to second object.

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Q70. What is the difference between Enumeration and Iterator ?

Ans. Enumeration can iterate only legacy collections like Vector , HashTable and Stack whereas Iterator can iterate both legacy and non legacy collections.

Enumeration is less safer than Iterator

Enumeration is fail safe whereas Iterator is fail fast

Iterator allows for removal of element while traversal whereas Enumeration doesn't have remove method.

Enumerations were introduced in Java 1 whereas Iterators were introduced with Java 2

Enumerations have methods like hasMoreElements and nextElement whereas Iterators have methods like hasNext, next and remove

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Q71. If an Abstract class has only abstract methods, What's the difference between such a class and an interface ?

Ans. Such a class still can have member elements which can be inherited and hence facilitate code reuse. Moreover Abstract class can have non final static elements whereas interfaces are only allowed to have static final elements.

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Q72. Write a Program to convert a binary to number ?

Ans. int convert(int binaryInt) {
int sumValue=0;
int multiple = 1;
while(binaryInt > 0) {
binaryDigit = binaryInt;
binaryInt = binaryInt /10;
sumValue = sumValue (binaryDigit * multiple);
multiple = multiple * 2;
}

return sumValue;
}

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Q73. How does java identifies which method to be called in method overriding or runtime polymorphism, when both methods share the same name and signature ?

Ans. Java identifies the method to be called at runtime by the object that is being referenced.

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Q74. Which of the two - compile time and run time polymorphism - requires signature of the method to be different ?

Ans. runtime polymorphism or method overriding doesn't require method name and signature to be different whereas compile time polymorphism or method overloading requires method name to be same but the signature to be different.

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Q75. What is the importance of Abstract Class ?

Ans. Abstract classes provide a mechanism of interfacing ( using abstract method ) as well as code reuse through inheritance ( extending abstract class )

Comparing to concrete class they have an advantage of providing interface which a concrete class doesn't provide.

Comparing to interfaces they have an advantage of providing code reuse through inheritance which interfaces dont provide.

Sample Code for abstract class

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Q76. What will happen if we don't have termination statement in recursion ?

Ans. It would result in endless function calls and hence eventually would result in stackoverflow exception.

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Q77. What is recursion in Java ?

Ans. It's a programming technique wherein the method can call itself. The method call usually involves a different set of parameters as otherwise it would lead to an infinite loop. There is usually a termination check and statement to finally return the control out of all function calls.

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Q78. What is JVM ?

Ans. JVM (Java Virtual Machine) is an abstract machine. It is a specification that provides runtime environment in which java bytecode can be executed.JVMs are available for many hardware and software platforms (i.e. JVM is platform dependent).Runtime Instance Whenever you write java command on the command prompt to run the java class, an instance of JVM is createdThe JVM performs following operation:Loads codeVerifies codeExecutes codeProvides runtime environment

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Q79. What will we get if we try to print local variable that hasn't been initialized ?

Ans. It will print the garbage value as compiler doesn't provide a default value to local variables.

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Q80. What is the precedence of operators in Java ?

Ans. http://introcs.cs.princeton.edu/java/11precedence/

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Q81. Write program to create a linked list and perform different operations on it.

Ans. import java.util.*;
class LinkedListSolution{
protected LinkedList list;
public LinkedListSolution(){
list = new LinkedList();
}
public Object pop() throws NoSuchElementException{
if(list.isEmpty())
throw new NoSuchElementException();
else
return list.removeFirst();
}
public void push(Object obj){
list.addFirst(obj);
}
public Object peek() throws NoSuchElementException{
if(list.isEmpty())
throw new NoSuchElementException();
else
return list.getFirst();
}
public boolean isEmpty(){
return list.isEmpty();
}
public String toString(){
return list.toString();
}
}
class TestStack{
public static void main(String args[]){
LinkedListSolution s = new LinkedListSolution();
s.push("First");
s.push("Second");
s.push("Third");
System.out.println("Top: " s.peek());
s.push("Fourth");
while(!(s.isEmpty()))
System.out.println(s.pop());
}
}

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Q82. What are some of the Java Naming conventions ?

Ans. 1. Class name should be a noun and should start with capital case character.

2. Interface Name should be an adjective and should start with capital case character.

3. Method and Variable names should follow lower camel case notation.

4. package name should be all lower case.

5. constant variables (static final) should be all capital case.

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Q83. What access the variable gets if we don't provide any access specifier ?

Ans. It gets the default access i.e package protected.

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Q84. What are the core OOPs concepts ?

Ans. Abstraction, Encapsulation, Polymorphism , Composition and Inheritance

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Q85. Write a Program to remove duplicate words from the String

Ans.
public class BuggyBread {
public static void main(String args[]) {
String str = "we are what we repeatedly Do excellence, then, is not an act but a haBit";
Set<String> wordSet = new LinkedHashSet(); // Using Linked Hash Set as we would like to retrieve words in the insertion order

for(String word: str.split(" ")){
wordSet.add(word);
}

for(String word: wordSet){
System.out.print(word);
System.out.print(" ");
}
}
}

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Q86. What are the different operators in Java ?

Ans. && - AND
|| - OR
! - LOGICAL NOT

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Q87. What are the different primitive data types in Java ?

Ans. boolean
byte
char
double
float
int
long
short
void

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Q88. Write any sorting algorithm.

Ans. https://javasearch.buggybread.com/InterviewQuestions/questionSearch.php?searchOption=label'

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Q89. What is the difference between authentication and authorization ?

Ans. Authentication is the process of verifying the identity and credentials of the user to authenticate him into the system.

whereas

Authorization is the process by which access to a segment , method or resource is determined.

Authorization is usually a step next to authentication.

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Q90. What is archiving ?

Ans. It's the process of preserving the state of an object and then restoring it.

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