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

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Q931. Why do you think lambda expressions are considered such a big thing for Java 8?

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Q932. What are the drawbacks of creating immutable objects ? Why don't we create all object immutable if mutability possesses so much threat ?

Core Java

Ans. Immutable objects relieves us from the problems of inconsistencies and security and helps with better read performance but at the same time are write performance and storage overheads. In case any modification is required , a new object is created and thus creating multiple copies of it.

This is the reason we use StringBuffer / StringBuilder when we have to append some text multiple times and then create a String out of it.

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Q933. 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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Q934. Do you think that Recursion is expensive on computation ?

Core Java

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Q935. 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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Q936. 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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Q937. 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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Q938. 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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Q939. Write a custom exception.

Core Java

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

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Q940. 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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Q941. Why use Java ?

Core Java

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Q942. Why do we need ConcurrentHashMap ?

Core Java

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Q943. What is the default size of ArrayList ?

Core Java

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Q944. 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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Q945. 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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Q946. What is the difference between Interfaces and Abstract Classes with respect to Java 8 ?

Core Java

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Q947. 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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Q948. 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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Q949. 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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Q950. Which are the thread safe / synchronized / concurrent classes in java collections ?

Core Java

Ans. Stack
Properties
Vector
BlockingQueue
ConcurrentMap
ConcurrentNavigableMap

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Q951. What are the differences between Intermediate and Terminal Operations in Java 8 streams?

Core Java

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Q952. What is the difference between Collections.emptyList() and creating instance of a list ?

Core Java

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Q953. Which are the classes that implement java.util.List interface ?

Core Java

Ans. ArrayList
LinkedList
Vector
Stack

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Q954. Why do you think that Stack collection class implement List interface ?

Core Java

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Q955. 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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Q956. What is difference between Executor.submit() and Executer.execute() method ?

Core Java

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Q957. What is difference between CyclicBarrier and CountDownLatch in Java ?

Core Java

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Q958. What do you mean by synchronized Non Access Modifier?

Core Java

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Q959. Name few classes of java.util.regex package ?

Core Java

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Q960. Is String thread-safe?

Core Java

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