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

Interview Questions and Answers - Order By Rating

Q61. Which Web and Application server is being used by your application ?

Server

Ans. We are using Apache 2.3 and Tomcat 5.6

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Q62. how to access the methods of an inner class?

Core Java

Ans. It depends on the type of inner class

To access non static inner class method

new OuterClass().new InnerClass().getMethod();

To access static method of static inner class

new OuterClass.InnerClass().getMethod();

Sample Code for inner class

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Q63. Which elements of a class are ignored during serialization ?

Core Java

Ans. 1. Objects are serialized and not classes and hence Static variables are ignored.

2. Transient is an explicit declaration to ignore the variable during serialization and hence transient instance variables are ignored too.

3. Base class instance variables if the base class hasn't been declared serializable.

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Q64. Which environment variables do we need to set in order to run Java programs?

Core Java

Ans. PATH, CLASSPATH and JAVA_HOME

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Q65. Explain various Searching and Sorting Algorithms ?

Algorithm

^{This question was recently asked at 'HeadStrong,ServiceNow'.This question is still unanswered. Can you please provide an answer.}

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Very frequently asked. Usually asked in this format or as difference with interfaces / concrete classes.

Q66. 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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Q67. What is the use of static keyword in Java ?

Core Java

Ans. static keyword is used to specify that the respective programming construct ( method , variable ) belongs to the class and not to its instance and is supposed to be shared by all instances of the class.

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Q68. What technical stuff you like to do in your free time ?

General

Ans. [Open Ended Answer]

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Frequently asked in Cognizant ( Based on 2 feedback )

Q69. What are Inner , Outer , Left and Right Joins in SQL ?

Database

Ans. Inner join is the intersection of two tables on the condition defined by the where clause i.e will get records from both tables matched by a column.

Outer join is the union of two tables i.e will get all records from both tables and will put null in the columns where related records are not present.

Left Outer join is the left union of two tables i.e all records from the table on the left and values from the right table for related records else null for the columns from right table.

Right Outer join is the right union of two tables i.e all records from the table on the right and values from the left table for related records else null for the columns from left table.

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Q70. What is an exception and exception handling in Java ?

Core 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.

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Q71. What is database Normalization ?

Database

Ans. https://en.wikipedia.org/wiki/Database_normalization

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Q72. Why java doesn't support multiple Inheritance ?

or

Explain Java Diamond Problem.

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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Q73. Which class is the root class of all Exceptions in Java ?

Ans. Throwable

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Q74. Name some of the Java Keywords ?

Core Java

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

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Q75. Explain some of the features of Java ?

Core 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.

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Q76. What do you look for when you do code review ?

Core Java

Ans. Modularity - First sign of good code is whether it has been segregated into methods and classes appropriately. I dont mind it in excess because I believe that is forward looking strategy as applications tends to expand and eventually become hard to read.

Self Explanatory - Variables and methods should be named in a way that the code should be self explanatory even without comments. Use of Constant variables to explain use of literal.

Proper Code Reuse - If there is anything being reused , it should be moved to parent classes / methods.

Proper composition calls - Composed hierarchy should not be access in just single line. One or two levels is ok but having multiple levels make it hard to read and debug.

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Q77. What is Maven ?

Maven

Ans. Maven is a build automation tool used primarily for Java projects.

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Q78. Explain some of the http status codes you know ?

Java EE

Ans. 500 is Internal Server Error

404 is resource not found

400 is Bad Request

403 is Forbidden

401 is Unauthorized

200 is OK

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Q79. What are Collection Classes ?

Core Java

Ans. Collections in java is a framework of classes that provides an abstracted data structure to store and manipulate the group of objects. Each class is unique in the way it stores , search , sort and modify the elements.

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Frequently asked in Accenture.

Q80. What is your biggest achievement at work ?

General

Ans. [Open Ended Answer]

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Q81. Difference between Error and Exception ?

Core Java

Ans. An Error indicates serious problems that a reasonable application should not try to catch whereas

An Exception indicates conditions that a reasonable application might want to catch.

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Q82. Difference between Array and ArrayList ?

Core Java

Ans. <a href="http://javahungry.blogspot.com/2015/03/difference-between-array-and-arraylist-in-java-example.html" rel="nofollow">http://javahungry.blogspot.com/2015/03/difference-between-array-and-arraylist-in-java-example.html</a>

Sample Code for ArrayList

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Q83. What is a web service ?

Java EE

Ans. A Web service is a service offered by one system to another, for communication over web through http. XML are JSON are usually used for sending across information from one system to another.

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Q84. Difference between relational databases and NoSQL databases ?

Database

Ans. https://www.mongodb.com/scale/nosql-vs-relational-databases

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Frequently asked in high end product companies. Frequently asked in Deloitte.

Q85. How is Hashmap internally implemented in Java ?

Core Java

Ans. https://medium.com/javarevisited/internal-working-of-hashmap-in-java-97aeac3c7beb#:~:text=HashMap%20internally%20uses%20HashTable%20implementation,the%20entries%20into%20the%20map.

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Very Frequently asked to Senior Software Engineers or Developers.

Q86. Describe some of the Design Patterns you have used ?

Design

Ans. [Open Ended Answer]

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Frequently asked Generic Question.

Q87. Why do you want to work for our company ?

General

Ans. [Open Ended Answer]

Usually answered stating your keen interest in the role offered and challenges and opportunities the role offers.

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Q88. Difference between Static and Singleton Class ?

Core Java

Ans. 1. Static class is a class which cannot be instantiated and all its members are static whereas Singleton is the class that only permit creation of single object and then the object is reused.

2. As there is no object in Static class, it cannot participate in runtime Polymorphism.

3. As Static class doesnt allow creating objects and hence it cannot be serialized.

4. Static class body is initialized eagerly at application load time whereas Singleton object can be initiated eagerly using static blocks or lazily on first need.

5. Its not recommended to use pure static class as it fails to use many OOPs concepts.

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Q89. Write a Program to check if 2 strings are Anagrams ?

Core Java

Ans. public void checkIfAnagram(String str1,String str2){
boolean anagram = true;
for(char c:str1.toCharArray()){
if(!str2.contains(String.valueOf(c))){
System.out.println("Strings are Anagrams");
anagram = false;
}

if(anagram == true){
System.out.println("Strings are not Anagrams");
}
}
}

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Q90. Explain Agile Software Development Methodology ?

Process

Ans. https://en.wikipedia.org/wiki/Agile_software_development

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