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

Interview Questions and Answers - Order By Newest

Q101. Whats the purpose of marker interfaces ?

Ans. They just tell the compiler that the objects of the classes implementing the interfaces with no defined methods need to be treated differently.

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

_{Like Discuss Correct / Improve java interfaces marker interfaces clonable serializable basic frequent}

Q102. What is the advantage of using arrays over variables ?

Ans. Arrays provide a structure wherein multiple values can be accessed using single reference and index. This helps in iterating over the values using loops.

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

_{Like Discuss Correct / Improve java arrays loops variables basic interview question}

Q103. What is a cloneable interface and what all methods does it contain?

Core Java

Ans. Cloneable is a declaration that the class implementing it allows cloning or bitwise copy of it's object state. It is not having any method because it is a MARKER interface.

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

_{Like Discuss Correct / Improve java oops cloneable marker interface cloning Asked in 2 Companies}

Q104. Are there any global variables in Java, which can be accessed by other part of your program?

Ans. No. Global variables are not allowed as it wont fit good with the concept of encapsulation.

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

_{Like Discuss Correct / Improve java variables global variables yes no}

Q105. What is connection pooling?

Database

Ans. It's a technique to allow multiple clients to make use of a cached set of shared and reusable connection objects providing access to a database or other resource.

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

_{Like Discuss Correct / Improve java jdbc db connectivity connection pooling architecture Asked in 3 Companies basic frequent}

Q106. Why is Java considered Portable Language ?

Core Java

Ans. Java is a portable-language because without any modification we can use Java byte-code in any platform(which supports Java). So this byte-code is portable and we can use in any other major platforms.

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

_{Like Discuss Correct / Improve java bytecode jvm compiler portable features of java basic interview question}

Q107. What data type Variable can be used in a switch statement ?

Core Java

Ans. Variables used in a switch statement can only be a byte, short, int, or char ( and String with Java 7 and above )

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

_{Like Discuss Correct / Improve java switch variable data type basic rare}

Q108. What is Comparable Interface?

Core Java

Ans. It is used to sort collections and arrays of objects using the collections.sort() and java.utils. The objects of the class implementing the Comparable interface can be ordered.

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

_{Like Discuss Correct / Improve java collections comparable interface Asked in 7 Companies intermediate frequent}

Try 1 Question(s) Test

Q109. What environment variables do I need to set on my machine in order to be able to run Java programs?

Ans. CLASSPATH and PATH are the two variables.

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

_{Like Discuss Correct / Improve java classpath path environment variables jvm}

Q110. Difference between Abstraction and Implementation hiding ?

Ans. Implementation Hiding is a broader concept. Abstraction is a way of implementation hiding in OOP's.

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

_{Like Discuss Correct / Improve java oops oops concepts abstraction hiding information build management}

Q111. What are the examples of Abstraction in Java ?

Ans. function calling - hides implementation details
wrapper classes
new operator - Creates object in memory, calls constructor

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

_{Like Discuss Correct / Improve java oops oops concepts abstraction}

Q112. How do you check memory leak in Java?

Core Java

Ans. You need to capture heap dump when it's in the healthy state. Start your application. Let it take real traffic for 10 minutes. At this point, capture heap dump. Heap Dump is basically the snapshot of your memory. It contains all objects that are residing in the memory, values stored in those objects, inbound

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

_{Like Discuss Correct / Improve memory leaks heap dump Asked in 1 Companies intermediate}

Q113. What is the use of HashCode in objects ?

Core Java

Ans. Hashcode is used for bucketing in Hash implementations like HashMap, HashTable, HashSet etc.

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

_{Like Discuss Correct / Improve java string hashcode hash code string comparison hashtable Asked in 17 Companies basic frequent}

Q114. Will static block for Test Class execute in the following code ?

class Test
{
static
{
System.out.println("Executing Static Block.");
}
public final int param=20;

public int getParam(){
return param;
}
}

public class Demo
{
public static void main(String[] args)
{
System.out.println(new Test().param);
}
}

Ans. Yes.

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

_{Like Discuss Correct / Improve java static static block final variable yes no}

Try 1 Question(s) Test

Q115. Difference between Inner and Outer Join ?

Database

Ans. Inner join is the intersection of two tables on a particular columns whereas Outer Join is the Union of two tables.

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

_{Like Discuss Correct / Improve sql joins inner join outer join Asked in 4 Companies basic frequent}

Q116. What is a Cursor ?

Database

Ans. It's a facility that allows traversal over the records pulled from a table or combination of tables. Its like iterator in Java.

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

_{Like Discuss Correct / Improve databases sql cursors packages Asked in 5 Companies basic frequent}

Q117. what will be the output ?

class Animal {
public void eat() throws Exception {
}
}

class Dog2 extends Animal {
public void eat(){}
public static void main(){
Animal an = new Dog2();
an.eat();
}
}

Core Java

Ans. Compile Time Error: Unhandled exception type Exception

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

_{Like Discuss Correct / Improve java code coding overridding late binding exception handling abstract class abstract methods}

Q118. Does SQL allow null values ? Can we use it within Where clause ?

Ans. Yes , we can have null values for columns in SQL. Null value represent that the columns value is unknown or haven't been filled. Yes, We can use it within where clause to get the rows with null values.

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

_{Like Discuss Correct / Improve sql sql null values sql where clause databases}

Q119. What is the problem with this code ?

class BuggyBread1 {

private BuggyBread2 buggybread2;

public static void main(String[] args){
try {
BuggyBread1 buggybread1 = new BuggyBread1();
ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(new File("newFile.txt")));
objectOutputStream.writeObject(buggybread1);
} catch (Exception e) {
e.printStackTrace();
}
}
}

Core Java

Ans. Though we are trying to serialize BuggyBread1 object but we haven't declared the class to implement Serializable.

This will throw java.io.NotSerializableException upon execution.

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

_{Like Discuss Correct / Improve java io file fileio coding code serialization notserializableexception exception file handling}

Q120. Will this code run fine if BuggyBread2 doesn't implement Serializable interface ?

class BuggyBread1 implements Serializable{
private BuggyBread2 buggybread2 = new BuggyBread2();

public static void main(String[] args){
try {
BuggyBread1 buggybread1 = new BuggyBread1();
ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(new File("newFile.txt")));
objectOutputStream.writeObject(buggybread1);
} catch (Exception e) {
e.printStackTrace();
}
}
}

Core Java

Ans. No, It will throw java.io.NotSerializableException.

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

_{Like Discuss Correct / Improve java io file fileio coding code serialization notserializableexception exception file handling}

Q121. Will this code Work ? If not , Why ?

java.util.Calendar c = new java.util.Calendar();

Core Java

Ans. No. It gives the error "Cannot Instantiate the type Calendar". Calendar is an abstract class and hence Calendar object should be instantiated using Calendar.getInstance().

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

_{Like Discuss Correct / Improve java date calendar abstract class yes-no}

Q122. Is java.util.Date an abstract Class ? Is java.util.Calendar an abstract Class ?

Core Java

Ans. Date is not a abstract class whereas Calendar is.

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

_{Like Discuss Correct / Improve java date calendar abstract class}

Very Frequently asked. Favorite question in walkins and telephonic interviews. Usually among first few questions. Asked in different variants. Must know for intermediate and expert professionals.Among Top 10 frequently asked questions.

Q123. What is rule regarding overriding equals and hashCode method ?

Core Java

Ans. A Class must override the hashCode method if its overriding the equals method.

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

_{Like Discuss Correct / Improve java collections hashcode hash code equals collections Asked in 44 Companies intermediate frequent}

Try 1 Question(s) Test

Q124. How TreeMap orders the elements if the Key is a String ?

Ans. As String implements Comparable, It refers to the String compareTo method to identify the order relationship among those elements.

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

_{Like Discuss Correct / Improve java collections comparable interface treemap compareto}

Q125. Can we add heterogeneous elements into TreeMap ?

Ans. No, Sorted collections don't allow addition of heterogeneous elements as they are not comparable.

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

_{Like Discuss Correct / Improve java collections comparable interface treemap}

Q126. Will it create any problem if We add elements with key as user defined object into the TreeMap ?

Ans. It won't create any problem if the objects are comparable i.e we have that class implementing Comparable interface.

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

_{Like Discuss Correct / Improve java collections treemap comparable interface}

Q127. Can we have null keys in TreeMap ?

Core Java

Ans. No, results in exception.

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

_{Like Discuss Correct / Improve java collections treemap Asked in 6 Companies Basic frequent}

Q128. What is the difference between these 2 annotations ?

@Entity ( name ="EMPLOYEES")
@Entity @Table ( name=""EMPLOYEES"" )

@Entity ( name="EMP")
@Table ( name="EMPLPYEES" )

Hibernate

Ans. First Annotation will set the Entity name as EMPLOYEES and hence will try to map with the same Table name.

The second annotation will make the Entity mapped to table EMPLOYEES irrespective of the Entity Name ( which is class name in this case ).

Third Annotations will set the different names for Enitity and Table and will explicitly map them.

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

_{Like Discuss Correct / Improve hibernate hibernate annotations entity annotation table annotation}

Q129. What is the difference between int[] x; and int x[]; ?

Core Java

Ans. No Difference. Both are the acceptable ways to declare an array.

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

_{Like Discuss Correct / Improve java array arrays array declaration difference between Asked in 3 Companies basic}

Very frequently asked. Usually followed by questions related to private constructor and synchronized access. Frequently asked in JPMorgan and TCS (Based on 2 feedback)

Q130. Explain Singleton Design Pattern ?

Design

Ans. http://www.buggybread.com/2014/03/java-design-pattern-singleton-interview.html

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

_{Like Discuss Correct / Improve java design pattern singleton at&t ebay fidelity india united healthcare india Asked in 46 Companies intermediate frequent}

Search Interview Questions

Help us and Others Improve. Please let us know the questions asked in any of your previous interview.