JAVA INTERVIEW QUESTIONS

Wednesday, 14 August 2013

JAVA: Deserializing an Object from File

To deserialize an object from file, first get the serialized data from the file using FileInputStream. In case if you want to know how to serialize an object to file please check this article serialize an object to a file. Pass the FileInputStream object through ObjectInputStream. Now, get the object from ObjectInputStream using the API readObject().

Example:

Suppose we have a file named sampleClass.ser which contains the data of a serialized object of class SampleClass. Please check this post to create this file. Where SampleClass is a normal pojo class with 4 variables, among which 1 is declared as transient, that means, protected from serialization.

Wednesday, 14 August 2013 by Anijit Sarkar · 3 Read more »

Sunday, 11 August 2013

JAVA: Keyword: abstract

abstract:

This is used to define a class or a method as an abstract operation. When a method is declared as abstract, that means, the method where it is declared (within the class) have no body of the method rather the method can be overridden, through inheritance and define it's body.
When a class contains any abstract method, it must be declared as abstract.
An abstract class cannot be final.
An abstract method cannot be final, static nor native.

Code:

package com.interview.question.java;

abstract class SampleAbstractClass {

/**

* Sample abstract class.

* @author http://interviewquestionjava.blogspot.com

// Sample abstract method.

public abstract void sampleabstractmethod() ;

public void sampleNormalMethod(){

System.out.println("SampleAbstractClass.sampleNormalMethod()");

}

public class TestAbstractClass{

/**

* Sample class to call SampleAbstractClass.

* @author http://interviewquestionjava.blogspot.com

public static void main(String[] args) {

SampleAbstractClass objSampleAbstractClass = newSampleAbstractClass() {

@Override

public void sampleabstractmethod() {

System.out

.println("TestAbstractClass.main(...).new SampleAbstractClass() {...}.sampleabstractmethod()");

}

};

objSampleAbstractClass.sampleabstractmethod();

}

Output:

TestAbstractClass.main(...).new SampleAbstractClass() {...}.sampleabstractmethod()

Sunday, 11 August 2013 by Anijit Sarkar · 6 Read more »

Sunday, 17 March 2013

SQL: OR Command

In SQL, we have seen the use of AND command, to set multiple condition when performing a database transaction. But when we use AND, that means it's a mandatory condition. The transaction will provide output, only when all the conditions will be satisfied. But, what about an optional condition? Do SQL have any provision for that? The Answer is yes. SQL Do have command named OR to set optional condition.

Syntax: SELECT [column_name] FROM [table_name] WHERE [condition_1] OR [condition_2];

Here, output will come if [condition_1] OR [condition_2] OR both satisfied. That means, it is SELECT [column_name] FROM [table_name] WHERE [condition_1] OR [condition_2] OR both applied.

Example:

Again, we will use the same table, to see the usage of OR command.
Table Name:
Employee Details ( employee_details)
Column Names:
Employee ID ( emp_id),
Employee Name (emp_name),
Employee Address (emp_address) and
Employee Role: (emp_role).

Table: employee_details

Now, using OR command, we will SELECT those tuple, WHERE emp_role is 'Developer' or 'Business Analyst'.
So, the query will be :

SELECT * FROM employee_details WHERE emp_role = 'Developer' OR emp_role = 'Business Analyst';

Result:

Sunday, 17 March 2013 by Anijit Sarkar · 0 Read more »

Friday, 1 March 2013

SQL: AND Command

In SQL, we have, seen that, we can add conditions by using WHERE command, during any SELECT, UPDATE or DELETE operation. Now, what about multiple conditions? For that, SQL provides to add multiple condition by using AND command. it can be used as many times as you want.

Syntax: SELECT [column_name] FROM [table_name] WHERE [condition_1] AND [condition_2];

[Note: AND means mandatory condition, that means, the operation has to always fulfill the criteria provied under AND block. ]

Example:

Again, use the same table, we will see the usage of AND command.
Employee Details ( employee_details), which contains
Employee ID ( emp_id),
Employee Name (emp_name),
Employee Address (emp_address) and
Employee Role: (emp_role).

Table: employee_details

Now, using AND command, we will SELECT those tuple, WHERE emp_role is 'Developer' and emp_address is 'Park Street, Kolkata'.
So, the query will be :

SELECT * FROM employee_details WHERE emp_role = 'Developer' AND emp_address = 'Park Street, Kolkata';

Result:

In this way, we can use multiple conditions on an RDBMS operation.

Friday, 1 March 2013 by Anijit Sarkar · 0 Read more »

Saturday, 23 February 2013

SQL: WHERE Command

In SQL,when ever you want to SELECT some data, or UPDATE or DELETE some information from a Table, you needs to provide some condition, on basis of which operation will be performed. It's not necessary to SELECT, UPDATE or DELETE all data from a table or view. So, condition is necessary to filter the data when performing an operation on database. The basic structure of of WHERE conditions is :

Syntax: SELECT [column_name] FROM [table_name] WHERE [condition]

Example:

Again, we will see the same table
Employee Details ( employee_details), which contains
Employee ID ( emp_id),
Employee Name (emp_name),
Employee Address (emp_address) and
Employee Role: (emp_role).

Table: employee_details

Now, from this table, if a situation ariser, where we have to just select the information of the developers, the we have to set some condition on our SELECT query, so that we can get the details of the employees with 'emp_role' 'Developer' . Then the Query will be

SELECT * FROM employee_details WHERE emp_role = 'Developer';

Result: