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 Q381. Does use of Final class enforces composition over Inheritance in Java ? Core Java
Ans. Yes, to a certain extent. But the objective for Final class could be beyond just enforcing composition as certain classes might have been created without inheritance or composition in mind.

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   Like         Discuss         Correct / Improve     final class   composition  object oriented programming (oops)  oops concepts  inheritance  object oriented programming (oops)  oops concepts  composition  object oriented programming (oops)  oops concepts vs inheritance  object oriented programming (oops)  oops concepts      expert

 Q382. What could be the reasons for restricting inheritance using final class ?Core Java
Ans. 1. Enforcing composition over inheritance
2. Restricting overriding of certain methods
3. Final methods are faster than regular instance methods
4. Enforcing Immutability

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   Like         Discuss         Correct / Improve     final class   reasons for final class   restricting inheritance  object oriented programming (oops)  oops concepts      expert

 Q383. Write code to create a folder if it doesn't exist.Core Java
Ans. File folder = new File(path);
      
if(!folder.exists()){
try {
folder.mkdir();
            
} catch (Exception e) {}
}

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   Like         Discuss         Correct / Improve     code  coding  file handling      basic

  Q384. Difference between Arrays and ArrayList ?Core Java
Ans. Both Arrays and ArrayLists are used to store elements. Elements can be either primitives or objects in case of Arrays, but only objects can be stored in Arraylist. Array is a fixed length data structure while arraylist is variable length collection class. Once created, you cannot change the size of the arrays, but arraylists can dynamically resize itself when needed.Another notable difference between Arrays and Arrayslist is that arary is part of core java programming and array list is part of collection classes

  Sample Code for arrays arraylist

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   Like         Discuss         Correct / Improve     array  arraylist  array vs arraylist     Asked in 7 Companies      basic        frequent

 Q385. Can we declare an array without assigning the size of an array? Core Java
Ans. No, It will throw compile time error saying "must provide either dimension expressions or an array initializer"

Alternatively we can provide array initializer like

String[] strArray = new String[]{"Buggy","Bread"};

which will initialize it to size 2 with values as "Buggy" and "Bread"


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   Like         Discuss         Correct / Improve     arrays  array initialization

 Q386. What is meant by "unreachable code" ? Can you write a code segment explaining this ?Core Java
Ans. Unreachable code is a code segment that can never be executed in any case. For example -

int x = 5;
return;
System.out.println(x);

In this code , 2nd line will return the control out of the method and hence 3rd line will never get executed and hence is unreachable code. This will be caught at compile time only.

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   Like         Discuss         Correct / Improve     unreachable code

 Q387. Why doesn't this code give compile time error when we are clearly trying to add an integer element to an array of Strings

Object[] strArray = new String[2];
strArray[0] = 5;		Core Java
Ans. Because the reference is of Object Array and the resolution of what it holds is identified at the runtime.

String[] strArray = new String[2];
strArray[0] = 5;

would have given the compile time array as the reference is of String array.

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   Like         Discuss         Correct / Improve     arrays

 Q388. What will happen if there are no interfaces in Java ?Core Java
Ans. Abstract classes can take care of that to a certain extent. Though they are little heavier than Interfaces but An abstract class with all abstract methods and no instance variables will be able to help with everything that currently an interface does.

The only problem is that a class can only extend one class whereas it can implements multiple interfaces and that is the reason Interfaces were introduced in Java, i.e to get over the problem of multiple inheritance.

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   Like         Discuss         Correct / Improve     interfaces      expert

 Q389. What are the biggest challenges for Java technology in the coming years?Core Java
Ans. JVM - With Cloud and Serverless, this could be a hurdle for it to be preferred technology.

Confusion between OOP and Functional Programming.

Slower speed of innovation due to wider adoption.

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 Q390. Difference between Base Class, Derived Class , Abstract Class and Concrete Class ?Core Java
Ans. Base Class is a relative term used to signify the Parent class in Parent - Child or Base - derived relationship.

Derived Class is a relative term used to signify the Child class in Parent - Child or Base - derived relationship.

Abstract Class is a class that is not allowed to be instantiated and hence can serve only a base class for it's usage.

Concrete Class is the class which is supposed to be instantiated and hence provide definition for all implementing interface methods and extending abstract methods.

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   Like         Discuss         Correct / Improve     Base Class   Derived Class    Abstract Class   Concrete Class

 Q391. why string pool concept for only String but not for StringBuffer ?Core Java
Ans. As String is immutable so by maintaining pool area we can refer the object to same area if they are with same content. But when it comes to string buffer or builder then due to mutable property if we do so then all the objects referring to that area will from now has new content.. So as to avoid this pool is present only in string.

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   Like         Discuss         Correct / Improve          Asked in 1 Companies

 Q392. why string pool concept for only String but not for StringBuffer ?Core Java
 This question was recently asked at 'oodles technology'.This question is still unanswered. Can you please provide an answer.


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 Q393. Difference between List and LinkedList ?Core Java
Ans. A List is an child interface of collection interface in java where as Linked list is and implementation class of List interface which has doubly linked as a underlying data structure

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   Like         Discuss         Correct / Improve     linkedlist  list vs linkedlist     Asked in 1 Companies

 Q394. What is concurrent interface ?Core Java
Ans. ConcurrentMap is an interface and it is a member of the Java Collections Framework. It represents a Map that is capable of handling concurrent access to it without affecting the consistency of entries in a map. ConcurrentMap interface present in java.util.concurrent package.

HashMap operations are not synchronized, while Hashtable provides synchronization. Though Hashtable is thread-safe, it is not very efficient. To solve this issue, the Java Collections Framework introduced ConcurrentMap in Java 1.5.

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   Like         Discuss         Correct / Improve     Concurrent Interface   java.util.concurrent   Java 8 Concurrency   java concurrency   java 8     Asked in 1 Companies

 Q395. Write a program to print next largest palindrome number? Core Java
 This question was recently asked at 'Ksolves'.This question is still unanswered. Can you please provide an answer.


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 Q396. Why cannot we initialize a final field within the constructor if the initialization is within try block ?Core Java
Ans. What if the initialization throws an exception. In that case , it will let it move forward without initializing the final field. So it's a way to enforce that either the field is initialized or it fails completely.

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   Like         Discuss         Correct / Improve     oops

  Q397. What is a cookie ?Java EE
Ans. A cookie is a small piece of text stored on a user's computer by the browser for a specific domain. Commonly used for authentication, storing site preferences, and server session identification.

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   Like         Discuss         Correct / Improve     cookie   javascript   web application   session management   browser   j2ee     Asked in 16 Companies      basic        frequent

 Q398. Can we reduce the visibility of the overridden method ?Core Java
Ans. No

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   Like         Discuss         Correct / Improve     overriding   access specifier   oops   java   yes-no

 Q399. What is servlet Chaining ?Java EE
Ans. Multiple servlets serving the request in chain.

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   Like         Discuss         Correct / Improve     java   web application   servlets     Asked in 1 Companies        rare

 Q400. Can static method access instance variables ?Core Java
Ans. Though Static methods cannot access the instance variables directly, They can access them using instance handler.

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   Like         Discuss         Correct / Improve     static   static method   java   oop   variables     Asked in 1 Companies      basic        frequent

Very frequently asked. Usually asked in this format or as difference with interfaces / concrete classes.
  Q401. What is an abstract class ?Core Java
Ans. Abstract class is the class that is not supposed to be instantiated. The purpose of the class to only have extension to the derived class.

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   Like         Discuss         Correct / Improve     abstract class     Asked in 6 Companies      basic        frequent

 Q402. Which interface does java.util.Hashtable implement?Core Java
Ans. Java.util.Map

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   Like         Discuss         Correct / Improve     java   collections   hashtable   map      basic        rare

Frequently asked.
  Q403. What is an Iterator?Core Java
Ans. Iterator is an interface that provides methods to iterate over any Collection.

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   Like         Discuss         Correct / Improve     java   collections   iterator     Asked in 11 Companies      basic        frequent

 Q404. Which interface provides the capability to store objects using a key-value pair?Core Java
Ans. java.util.map

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   Like         Discuss         Correct / Improve     java   collections   map      basic        frequent

 Q405. Does java allow overriding static methods ?Core Java
Ans. No. Static methods belong to the class and not the objects. They belong to the class and hence doesn't fit properly for the polymorphic behavior.

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   Like         Discuss         Correct / Improve     java   oops   static   static method   overriding      intermediate
Try 3 Question(s) Test

 Q406. Difference between long.Class and Long.TYPE ?
Ans. They both represent the long primitive type. They are exactly the same.

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   Like         Discuss         Correct / Improve     java   data types   long.Class   long.TYPE   advanced      expert        rare

 Q407. Does Java provides default copy constructor ?Core Java
Ans. No

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   Like         Discuss         Correct / Improve     java   constructor   copy constructor   yes-no

Frequently asked to fresh graduates.
 Q408. What are the difference between Threads and Processes ?Operating System
Ans. 1. when an OS wants to start running program it creates new process means a process is a program that is currently executing and every process has at least one thread running within it.
2). A thread is a path of code execution in the program, which has its own local variables, program counter(pointer to current execution being executed) and lifetime.
3. When the JavaVirtual Machine (JavaVM, or just VM) is started by the operating system, a new process is created. Within that process, many threads can be created.
4. Consider an example : when you open Microsoft word in your OS and you check your task manger then you can see this running program as a process. now when you write something in opened word document, then it performs more than one work at same time like it checks for the correct spelling, it formats the word you enter , so within that process ( word) , due to different path execution(thread) all different works are done at same time.
5. Within a process , every thread has independent path of execution but there may be situation where two threads can interfere with each other then concurrency and deadlock come is picture.
6. like two process can communicate ( ex:u open an word document and file explorer and on word document you drag and drop another another file from file explorer), same way two threads can also communicate with each other and communication with two threads is relatively low.
7. Every thread in java is created and controlled by unique object of java.lang.Thread class.
8. prior to jdk 1.5, there were lack in support of asynchronous programming in java, so in that case it was considered that thread makes the runtime environment asynchronous and allow different task to perform concurrently.

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   Like         Discuss         Correct / Improve     java   operating system   threads   processes     Asked in 2 Companies        frequent

 Q409. Why java doesn't support multiple Inheritence ?Core Java
Ans. class A {
void test() {
System.out.println("test() method");
}
}

class B {
void test() {
System.out.println("test() method");
}
}

Suppose if Java allows multiple inheritance like this,

class C extends A, B {
}

A and B test() methods are inheriting to C class.

So which test() method C class will take? As A & B class test() methods are different , So here we would Facing Ambiguity.

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   Like         Discuss         Correct / Improve     java   oops   inheritence   multiple inheritence     Asked in 1 Companies      basic        frequent

Usually asked only to fresh graduates.
 Q410. Why threads block or enters to waiting state on I/O?Operating System
Ans. Threads enters to waiting state or block on I/O because other threads can execute while the I/O operations are performed.

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   Like         Discuss         Correct / Improve     java   threads   multithreading   scheduling   operating system

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