Interview Questions and Answers for 'Java' | Search Interview Question

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Q371. Name few classes of java.util.regex package ?

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Q372. What do you mean by synchronized Non Access Modifier?

Core Java

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Q373. What is difference between CyclicBarrier and CountDownLatch in Java ?

Core Java

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Q374. What is difference between Executor.submit() and Executer.execute() method ?

Core Java

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Q375. What is the there only one method declared in Runnable interface?

Core Java

Ans. The Runnable interface describes a class whose instances can be run as a thread. The interface itself is very simple, describing only one method ( run ) that is called automatically by Java when the thread is started. The Runnable interface is usually used in conjunction with the Thread class.

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Q376. Why do you think that Stack collection class implement List interface ?

Core Java

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Q377. Which are the classes that implement java.util.List interface ?

Core Java

Ans. ArrayList
LinkedList
Vector
Stack

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Q378. What is the difference between Collections.emptyList() and creating instance of a list ?

Core Java

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Q379. What are the differences between Intermediate and Terminal Operations in Java 8 streams?

Core Java

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Q380. Which are the thread safe / synchronized / concurrent classes in java collections ?

Core Java

Ans. Stack
Properties
Vector
BlockingQueue
ConcurrentMap
ConcurrentNavigableMap

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Q381. What is the reason that non-static method are not allowed to be referenced from a static context in Java?

Core Java

Ans. If we try to access an instance method from a static context , the compiler has no way to guess which instance method ( variable for which object ), you are referring to. Though, you can always access it using an object reference.

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Q382. Which of the OOP's feature is most important ?

Core Java

Ans. Encapsulation facilitate hiding and restricted access and hence more of a security feature. Encapsulation is definitely a great feature as when applications expand criss cross communication between objects / modules could lead to blunders.

Inheritance facilitates code reuse.

Polymorphism comprise of method overloaded ( which to me is negligible usage ) and method overriding. Method overriding is of great usage as it facilitates concept of interfaces and plugin development.

So it’s Security / Organization vs

Code Reuse / Support for other features like overriding vs

Contracts / Plugin Development facilitating the creation of frameworks / libraries.

Which is more important may vary from application to application , its scale , its use , its sensitivity etc.

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Q383. Which of the polymorphism type - static or runtime - is more important ?

Core Java

Ans. Method overloading / static polymorphism compared to method overriding / runtime polymorphism has very limited usage as it just opens up an alternate way of defining a different method with the same name.

Method Overriding on other hand opens up many other features like contracting , interfacing , pluging development and hence development of libraries and frameworks.

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Q384. Which of the OOP's feature - encapsulation or abstraction - is more important ?

Core Java

Ans. Encapsulation facilitates security by hiding data and logic whereas Abstraction simplifies organization of data and related logic.

As applications scale, both concepts are required for easy management and maintenance. Encapsulation for security and criss cross communication between objects / modules will make it vulnerable. and Abstraction for better organization that enables better understanding of application code and easy maintainability.

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Q385. What is the difference between Interfaces and Abstract Classes with respect to Java 8 ?

Core Java

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Q386. What is the need for filters in Java Servlets ?

Java EE

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Q387. Write code to read data from a file and write it to a file with 2 threads using the thread name content

Core Java

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Q388. Find minimum operations required to convert one string to another. Allowed operation :Insertion Deletion Replace, all operational costs are same.

Core Java

Ans. StringBuilder str = new StringBuilder("Pizza");
int size = str.length();
str = str.replace(size-1, size, "u");
System.out.println("After replace, str = " str); // prints Pizzu

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Q389. What is the default size of ArrayList ?

Core Java

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Q390. Why do we need ConcurrentHashMap ?

Core Java

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Q391. Is HttpServlet an abstract class ?

Java EE

Ans. Yes

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Q392. Why use Java ?

Core Java

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Q393. What is an exception ? What are the different types of exceptions ?

Core Java

Ans. An exception is an unwanted or unexpected event, which occurs during the execution of a program that is at run time, that disrupts the normal flow of the program?s instructions. these are different types arithmetic exceptions, class not found exception, interrupted exception, run time exception etc.

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Q394. Write a custom exception.

Core Java

Ans. if you are creating your own exception is known as custom exception.

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Q395. Write a program to find length of String without using library function.

Core Java

Ans. Class lengofstring {
Public static void main(String[] arr) {
int i = 0;
String s = "hello world!";
for (char C: s.toCharArray()) i;
System.out.println("Length: "
i);
}
}

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Q396. Write a program to find the 10th prime number.

Core Java

Ans. import java.util.Scanner;
public class Prime
{
public static void main(String[] args)
{
Scanner sc = new Scanner(System.in);
System.out.print("Enter n to compute the nth prime number: ");
int nth = sc.nextInt();
int num, count, i;
num=1;
count=0;

while (count < nth){
num=num 1;
for (i = 2; i <= num; i )
{
if (num % i == 0)
{
break;
}
}
if ( i == num)
{
count = count 1;
}
}
System.out.println("Value of nth prime: " num);
}
}

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Q397. Given an array with number 1 to n, find the missing numbers.

Core Java

Ans. int main ()
{
int a []={1..n};
int miss=getMiss (a,n);
Printf ("%d",miss);
}
getMiss (int a [],int n){
int I,total;
total=(n 1)*(n 2);
for (i = 0; i < n; i++)
total -= a[i];
return total;
}

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Q398. Write a program to rotate array elements clockwise.

Core Java

Ans. class Rotate{

void leftRotate(int arr[], int d, int n)
{
for (int i = 0; i < d; i )
leftRotatebyOne(arr, n);
}

void leftRotatebyOne(int arr[], int n)
{
int i, temp;
temp = arr[0];
for (i = 0; i < n - 1; i )
arr[i] = arr[i 1];
arr[i] = temp;
}

void printArray(int arr[], int n)
{
for (int i = 0; i < n; i )
System.out.print(arr[i] " ");
}

public static void main(String[] args)
{
Rotate rotate = new Rotate();
int arr[] = { 1, 2, 3, 4, 5, 6, 7 };
rotate.leftRotate(arr, 2, 7);
rotate.printArray(arr, 7);
}
}

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Q399. Do you think that Recursion is expensive on computation ?

Core Java

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Q400. Does immutability facilitates better performance ?

Core Java

Ans. Yes , but only the read performance in case we don't need to modify it much. In case we need to modify it a lot , it creates write performance overheads as we would need to create many news objects instead of just changing one.

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