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

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

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

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().

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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.

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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.

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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.

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Q125. Can we add heterogeneous elements into TreeMap ?

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

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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.

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Q127. Can we have null keys in TreeMap ?

Core Java

Ans. No, results in exception.

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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.

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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.

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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

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Q131. Write an SQL to find all records having all upper case alphanumeric characters in a field ?

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

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Q132. Write an SQL to find all records having all numeric characters in a field ?

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

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Q133. 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

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Q134. 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.

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Q135. What is Closeable ?

Core Java

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

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Q136. 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.

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Q137. 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 ).

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Q138. 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.

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Q139. 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.

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Q140. How can we disable a constraint ?

Database

Ans. alter table
table_name
DISABLE constraint
constraint_name;

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Q141. 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.

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Q142. What should be done for auto generating primary key id in a table ?

Database

Ans. We need to create a sequence.

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Q143. Which constraint cannot be specified as an explicit constraint and should be specified with the column only ?

Database

Ans. NOT NULL

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Q144. 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.

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Q145. 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".

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Q146. How to know the structure of a Table in Oracle ?

Database

Ans. DESC

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Q147. How to know the constraints on a Table in Oracle ?

Database

Ans. SELECT *
FROM user_constraints
WHERE table_name = ''

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Q148. How to know the default column value of a Table in Oracle ?

Database

Ans. Select DATA_DEFAULT
from DBA_TAB_COLUMNS
where TABLE_NAME = '' and COLUMN_NAME='';

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Q149. How do we specify the criteria if it involves mapping between two entities or join between tables ?

Hibernate

Ans. The following code returns the list of Employee objects having employee name starting with A and Dept Name ( Department , Employee Mapped ).

session.createCriteria(Employee.class,"emp")
.createAlias("emp.department", "dept",Criteria.INNER_JOIN)
.add( Restrictions.like("name", "A%") )
.add(Restrictions.eq("dept.name","Finance")
.list();

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Q150. Name few classes that implement Cloneable interface ?

Ans. http://www.buggybread.com/2015/02/java-collections-classes-that-implement_58.html

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