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

Interview Questions and Answers - Order By Newest

Q121. 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}

Q122. 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}

Q123. 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}

Q124. 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}

Q125. 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}

Q126. 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.

Q127. 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

Q128. 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}

Q129. 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}

Q130. 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}

Q131. 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}

Q132. 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}

Q133. 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)

Q134. 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}

Q135. Write an SQL to find all records having all upper case alphanumeric characters in a field ?

Ans. Select * from Table where field = upper(field)

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

_{Like Discuss Correct / Improve sql database}

Q136. Write an SQL to find all records having all numeric characters in a field ?

Ans. Select * from Table where isnumeric(field) = 1;

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

_{Like Discuss Correct / Improve sql database}

Q137. What are the conventions regarding constant variables or static final variables ?

Core Java

Ans. They should be named all in upper case with underscore separating words.

Moreover the name should be such that it identifies the value. For example, if we are using constant for employee Id 123, it should be named something like EMPLOYEE_ID_123 and not EMPLOYEE_ID

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

_{Like Discuss Correct / Improve constants variable names java conventions}

Q138. Do you know of any DB statement that can be used if we would like to insert multiple rows into a table ?

Database

Ans. We can use INSERT ALL.

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

_{Like Discuss Correct / Improve database insert dml statement sql}

Q139. What is Closeable ?

Core Java

Ans. A Closeable is an interface which is a source or destination of data that can be closed.

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

_{Like Discuss Correct / Improve closeable interfaces intermediate rare}

Q140. What is the advantage of JPA ?

Database

Ans. Its a specification that guides the implementation of ORM frameworks. Implementations abiding by the specification would mean that one can be replaced with other in an application without much hassle. Only the Features that are added over the specification needs to be taken care of if any such change is made.

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

_{Like Discuss Correct / Improve jpa hibernate orm technologies}

Q141. Why is a constant defined as a static final in Java?

Core Java

Ans. Final makes sure that the value doesn't change after initialization and static makes sure that there is only one copy that can be shared across objects.

Making it non static will unnecessarily create a different copy per object wherein the same value will kept for all copies ( as its final and cannot be changed ).

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

_{Like Discuss Correct / Improve java static final variables variable constants basic frequent}

Q142. What things you will look for if you get following exception while making DB call ?

table or view does not exist

Database

Ans. First will check if the table or view actually exist in the DB

If it does , Will make sure to see that the application has rights on the schema that holds the respective Table.

Will then make sure that we have prefixed the schema with the table name while accessing it.

Will then make sure that its not DB Cache that's causing it as the table DDL might have been created recently.

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

_{Like Discuss Correct / Improve sql database oracle technical lead}

Q143. What's the benefit for specifying constraints like Not Null , Primary Key explicitly instead of specifying it against the column ?

Database

Ans. In case we specify them explicitly we can have control over constraint name as otherwise they will be system generated. It provides an ease in case we plan to drop the constraint in future.

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

_{Like Discuss Correct / Improve sql database oracle}

Q144. How can we disable a constraint ?

Database

Ans. alter table
table_name
DISABLE constraint
constraint_name;

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

_{Like Discuss Correct / Improve sql database oracle}

Q145. Can we have foreign key reference to a non primary key column ?

Database

Ans. Yes, but the respective key in the foreign table should be declared Unique.

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

_{Like Discuss Correct / Improve sql database oracle Asked in 2 Companies}

Q146. What should be done for auto generating primary key id in a table ?

Database

Ans. We need to create a sequence.

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

_{Like Discuss Correct / Improve sql database oracle}

Q147. Which constraint cannot be specified as an explicit constraint and should be specified with the column only ?

Database

Ans. NOT NULL

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

_{Like Discuss Correct / Improve sql oracle database ddl constraint table creation}

Q148. Will this code compile ?

public class BuggyBread1{
abstract public void test();
}

Core Java

Ans. No. It will give the compilation error saying "The abstract method test in type BuggyBread1 can only be defined by an abstract class".

We need to declare the class abstract for it to have any abstract method.

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

_{Like Discuss Correct / Improve java oops abstract class abstract methods java compilation error}

Q149. Will this Code compile ?

abstract public class BuggyBread1{
abstract public void test(){};
}

Core Java

Ans. No. This will give a compilation error saying "Abstract methods do not specify a body".

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

_{Like Discuss Correct / Improve java abstract classes abstract methods java compilation error java coding java code coding yes-no}

Q150. How to know the structure of a Table in Oracle ?

Database

Ans. DESC

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

_{Like Discuss Correct / Improve sql database oracle}

Search Interview Questions

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