Core Java - Interview Questions and Answers for 'Core Java' | Search Interview Question - javasearch.buggybread.com

Javasearch.buggybread.com

Search Interview Questions

More than 3000 questions in repository.

There are more than 900 unanswered questions.
Click here and help us by providing the answer.

Have a video suggestion.
Click Correct / Improve and please let us know.

Submit Question

Interview Questions and Answers - Order By Newest

next 30

Q551. Write a Program to print the positive and negative numbers separetly

Ans. int[] arr = {1,-1,2,-3,3,-4,4,5,6,-5,-6,-7,-8,8,9,-9};
List positiveNumbers = new ArrayList<>();
List negativeNumbers = new ArrayList<>();
for(int i = 0; i < arr.length(); i ){
if(I < 0){
negativeNumbers.add(i);
} else {
positiveNumbers.add(i);
}
}

System.out.println("Positive Numbers:" + positiveNumbers);
System.out.println("Negative Numbers:" + negativeNumbers);

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve code program coding Asked in 1 Companies}

Q552. What could be the problems due to the usage of static methods and elements ?

Ans. static methods and static elements are shared by all objects of a class and hence could create problem.

Static methods are not synchronized by default and hence could create problem when accessed through multiple threads. Static elements are shareable by class and hence state of one object could be altered by another object.

Some limitations with Unit testing as not all mocking framework facilitate mocking them. Power mock allows but Mockito doesn't

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve static static method static variables}

Q553. What is the advantage of using static final or constant variables in Java ?

Ans. Better Control - If the value is being used at multiple locations , that can be controlled better from single place. Any change would only require making single change.

Meaning , Aliasing and Better Readability - Sometimes its easy to read the value by its meaning or alias ( 0 as ZERO or 0 as NEUTRAL_VALUE ).

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve static final final variable variable constants}

Q554. What is serialVersionUID ?

Ans. Everytime an object is serialized the java serialization mechanism automatically computes a hash value by passing the meta information for the class. This id is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve serialVersionUID serialization Asked in 3 Companies expert rare}

Q555. How to make sure that only one instance is created in Singleton Pattern ?

Ans. public class SingleTon {
private SingleTon() {
if (singleTon != null) {
throw new RuntimeException("cant not create the object");
}
}
public Object clone() throws CloneNotSupportedException {
throw new CloneNotSupportedException("can not be create");
}

static private volatile SingleTon singleTon;
public static SingleTon getInstance() {
SingleTon singleTon = this.sample;
if (singleTon == null) {
synchronized (this) {
singleTon = this.singleTon;
if (singleTon == null) {
singleTon = this.singleton = new SingleTon();
}
}
}
return singleTon;
}
}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve singleton design pattern Asked in 2 Companies}

Q556. Provide an implementation for Producer / Consumer using threads.

Ans. https://www.tutorialspoint.com/javaexamples/thread_procon.htm

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve coding code Asked in 1 Companies}

Q557. When should we use Abstract classes ?

Ans. Abstract classes provide a mechanism of interfacing ( using abstract method ) as well as inheritance ( extending abstract class ). So they should be used in place of interfaces in case there is some code ( methods ) or object body ( member elements ) that can be reused with inheritance.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve abstract classes Asked in 1 Companies}

Q558. What is the difference between following code segments

1.

try {
for(int i=0;i<100;i++){
calculate(i);
}
} catch (Exception ex) {
System.out.println("Error while processing")
}

and

2.

for(int i=0;i<100;i++){
try {
calculate(i);
} catch (Exception ex) {
System.out.println("Error while processing")
}
}

Ans. In first case the whole loop will terminate as soon as any exception happens in the method calculate ( assuming calculate method is not handling its exception and those are thrown back at the calling method )

In Second case exception will be caught for individual iteration and hence it wont break the loop and will continue for the next iteration.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve exception handling try catch Asked in 1 Companies}

Q559. What will be the output of following code

public class BuggyBread {
   static class A {
      A() {
         f();
      }

      public void f() {
         System.out.println("A ctor");
      }
   }

   static class B extends A {
      B() {
         f();
      }

      public void f() {
         System.out.println("B ctor");
      }
   }

   public static void main(String[] args) {
      B b = new B();
      b.f();
      A a = new A();
      a.f();
   }
}

Ans. B ctor
B ctor
B ctor
A ctor
A ctor

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Asked in 1 Companies}

Q560. Explain some of the features of Java ?

Ans. Object Oriented - Java is object oriented but isn't purely object oriented as we have primitives along with objects.

Platform Independent - As JVM provides the translation to the Machine code as per the underlying Operating System.

Interpreted as well as compiled - Java files are compiled as class files and then class files are interpreted by JVM.

Runs on a Virtual Machine - Which is JVM that acts as an independent sub environment.

Multi-threaded - As applications can run on single thread as well as multi thread.

Modularity - Through usage of Classes , methods and Interfaces.

Robust

Usage in variety of Application types - Web , Gaming, BigData.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve frequent}

Q561. Name some of the Java Keywords ?

Ans. Static , Final , Synchronized, private , public , protected, volatile, transient, super, this,import , abstract,native,default (effective java 8), new

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java keywords frequent}

Q562. Which operators in Java have highest precedence ?

Ans. Braces, i.e () and [] have the highest precedence

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java operators}

Q563. What is an exception and exception handling in Java ?

Ans. An Exception in java is the occurrence during computation that is anomalous and is not expected.

Exception handling is the mechanism which is used to handle such situations.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve exception handling Asked in 18 Companies basic frequent}

Q564. How is hashcode calculated in java ?

or

What are the rules for hashcode calculation ?

Ans. General contract of hashCode is:

1.Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer,

2.If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.

3.It is not required that if two objects are unequal according to the equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve hashcode Asked in 1 Companies expert}

Q565. Why main method is declared static ?

Ans. static is the keyword that makes it accessible even without creating any object and using class name only. Making it non static would like creation of object upfront before calling the method.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve main method static Asked in 4 Companies Basic}

Q566. Create a Class Bank with the methods to deposit and Withdraw ?

Ans. class Bank {
int balance;

Bank(){
balance = 0;
}

void deposit(int amount){
balance = balance amount;
}

int withdraw(int amount){
balance = balance - amount;
return balance;
}
}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Asked in 1 Companies Basic}

Frequently asked in high end product companies.

Q567. Write code for LRU Cache

Ans. https://www.geeksforgeeks.org/lru-cache-implementation/

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve cache LRU cache coding code Asked in 10 Companies intermediate}

Q568. Can a constructor throw an exception ?

Ans. Yes

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Asked in 1 Companies}

Q569. Can constructor be synchronized in Java ?

Ans. No, constructors can not be synchronized in Java. In fact using the keyword synchronized with a constructor results in compilation error.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Asked in 1 Companies expert}

Q570. Will finally run if we have return statement and it exits the method early ?

Ans. finally will execute in all graceful situations - graceful executions as well as graceful exceptions. The only situation when finally block won't execute is when the app is abruptly stopped, killed or unplugged.

Sample Code for finally

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve finally Intermediate}

Q571. Is it mandatory to have a default constructor ?

Ans. No.

Default constructor is provided by compiler if no constructor is provided ( argument or no argument ) by us.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve constructor default constructor Asked in 1 Companies}

Try 1 Question(s) Test

Q572. Which environment variables do we need to set in order to run Java programs?

Ans. PATH, CLASSPATH and JAVA_HOME

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve environment variables path classpath java_home Asked in 3 Companies basic frequent}

Q573. Can an application have multiple main methods within different classes ? If yes, How will the app decide which one to be executed ?

Ans. Yes we can have a main method with string[] argument in every class of an application. When we execute an app we specify the starting point i.e the class that will get the control first and hence main method of that class gets executed.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve main method Asked in 3 Companies}

Q574. Does importing a package imports all its sub packages too ?

Ans. No, but we can use wild card (*) to do so

For example -

import java.util.*

will import all packages with name starting with java.util

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve package import packages Asked in 1 Companies basic}

Q575. What is the default value of a declared object reference ?

Ans. Null

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve object reference null Asked in 1 Companies basic}

Q576. Is there a way to know size of an object in Java ?

Ans. No, Java doesn't have a sizeOf operator. In C / C++ , its required to determine how much memory allocation is required which is not the case with Java. Java handles memory allocation and deallocation intrinsically.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve sizeOf size of object sizeOf operator Asked in 1 Companies rare}

Q577. What are the different ways to handle an exception ?

Ans. 1. Wrap the desired code in try block followed by a catch / finally to catch the exception

2. Declare the throws clause with exceptions that the code is expected to throw as an indication to the calling method to take care of it.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve exception handling Asked in 4 Companies}

Try 1 Question(s) Test

Q578. How does Java handle integer overflows and underflows?

Ans. It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve integer data types Asked in 1 Companies rare}

Q579. Is delete a keyword in Java ?

Ans. No, delete is not a keyword in Java. Destruction of objects is taken care by Java Garbage Collection mechanism.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve delete keywords Asked in 1 Companies}

Q580. Is exit a keyword in Java ?

Ans. No exit is a method to exit execution of a program.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve exit keywords exit a program Asked in 1 Companies}

previous 30

next 30