Technology World

Tuesday, August 14, 2018

Java Interview Questions and Answers - Part I

Are you looking for which questions are asked during a Java interview? If so, then refer to this question and answer article on Java and supporting technologies. This article explains all Java related concepts in detail. This is the first article of the Java Interview Questions and Answers series.

Q1: What are the differences between Java and C++?
Answer:

Sr. No.	Java	C++
1	Java does not support pointers. Pointers are inherently tricky to use and troublesome.	C++ supports pointers.
2	Java does not support multiple inheritances because it causes more problems than it solves.	C++ supports multiple inheritances.
3	Java does not support destructors but adds a finalize() method. Finalize methods are called by the garbage collector prior to reclaiming the memory occupied by the object.	C++ supports destructors which are automatically invoked when the object is destroyed.
4	Java does not include structures or unions because the traditional data structures are implemented as an object oriented framework.	C++ includes structures.
5	Java includes automatic garbage collection.	C++ requires explicit memory management.
6	Java has built in support for threads. In Java, there is a Thread class that you inherit to create a new thread and override the run() method.	C++ has no built in support for threads. C++ relies on non-standard third-party libraries for thread support.
7	Pointers, references, and pass-by-value are supported for all types (primitive or user-defined).	All types (primitive types and reference types) are always passed by value.

Q2: Explain the Java Platform.
Answer:

It is a software-only platform and it runs on top of other hardware-based platforms like UNIX, NT etc.
Java has a set of classes written in the Java language. Such classes are called the Java Application Programming Interface (Java API). It runs on the Java Virtual Machine.
Java Virtual Machine (JVM) is a software that is installed on the hardware platforms. JVM uses Byte codes as the machine language.

Q3 : What are the uses of Java packages?

Answer:

Java package is a namespace. It helps to group a set of related classes and interfaces together. e.g. java.lang package is used to group classes to the design of the Java programming language. Packages play a significant role in resolving conflicts in class names.

For example, in the real time world we keep documents in one folder, images are kept in a separate folder and scripts or code are kept in a different folder. Packages keep classes in different packages for better organization of source code and also to resolve conflicts if class names are the same.

In order to create a package for your class use the statement below as the first statement -

package com.abc.pqr;

Here, package is the keyword in Java and com.abc.pqr is the package name.

If you are going to import any other class then import the package in your class as,

import java.io.*;

Q4: What is Classpath in Java?

Answer: Classpath is a parameter in the Java Virtual Machine. It specifies the location of user-defined classes and packages. It can be set either on the command-line or through an environment variable.

Have you noticed the error below while running the Java program?

Exception in thread "main" java.lang.NoClassDefFoundError: com/abc/pqr/MyWorld

If so, then you have not set the classpath in your system. To resolve this issue you can use one of the approaches below -

1. Set your project in the CLASSPATH environment variable of your system. e.g. "c:/TestProject"

2. Set the jar file of your project in the CLASSPATH environment variable of your system. This jar file should contain your .class file.to have a jar file e.g. we need to set the "c:/TestProject/HelloWorld.jar"" jar file in CLASSPATH and this .jar file has the MyWorld.class file in it.

3. Run it with –cp or –classpath commands as shown below:

c:\>java –cp c:/TestProject com.abc.pqr.MyWorld

c:\>java -classpath c:/TestProject/HelloWorld.jar com.abc.pqr.MyWorld

Q5: What are the advantages of the Object Oriented Approach?

Answer: Java is the Object Oriented Language and it comes with the benefits mentioned below due to its Object Oriented approach:

We can achieve code re-usability with help of implementation inheritance and object composition.
Everything in Java is an object and it maps to the real world. E.g vehicles, customers
It helps to create modular architecture with the help of objects, systems, frameworks etc which are the building blocks of the big application.
An Object Oriented Program forces designers to go through an extensive planning phase, which makes for better designs with less flaws.
An Object Oriented Program is much easier to modify and maintain than a non-Object Oriented Program.

Thursday, August 9, 2018

Important File and Directory permissions in Unix

Are you looking for how permissions works in the Unix Operating system? Would you be interested in knowing what types of permissions are available in the Unix environment? The details about permissions in the Unix are explained in this article. This article also provides highlights on various characteristics about File and Directory permissions.

What are the types of file permissions?

The file permissions categories are as follows:

Owner permissions − It determines what actions the owner of the file can perform on the file.
Group permissions − It determines what actions a user, who is a member of the group to which a file belongs, can perform on the file.
Other (world) permissions − It indicates what action all other users can perform on the file.

How to display Permissions?

To display permissions on screen use ‘ls –l’ command -> read (r), write (w), execute (x) e.g.

ls –l /usr/tmp

-rwxr-xr-- 1 testuser users 1017 Jan 2 00:10 myfile

drwxr-xr-- 1 testuer users 1017 Jan 2 00:10 mydir

Here, the first column represents different access modes, i.e., the permission associated with a file or a directory. The first character ‘-‘ stands for the file and the character ‘d’ stands for the directory.
The first three characters (2-4) represent the permissions for the file's owner. For example, -rwxr-xr-- represents that the owner has read (r), write (w) and execute (x) permission.
The second group of three characters (5-7) consists of the permissions for the group to which the file belongs. For example, -rwxr-xr-- represents that the group has read (r) and execute (x) permission, but no write permission.
The last group of three characters (8-10) represents the permissions for everyone else. For example, -rwxr-xr-- represents that there is read (r) only permission.

Understanding File access modes

There are three types of file access modes: Read, Write and Execute. Mentioned below are the details about each mode:

Read : Grants the capability to read, i.e., view the contents of the file.
Write: Grants the capability to modify or remove the content of the file.
Execute: User with execute permissions can run a file as a program.

Understanding Directory access mode

There are three types of directory access modes: Read, Write and Execute. Mentioned below are the details about each mode:

Read: Access to a directory means that the user can read the contents. The user can look at the filenames inside the directory.
Write: Access means that the user can add or delete files from the directory.
Execute: Executing a directory doesn't really make sense, so think of this as a traverse permission. A user must have execute access to the bin directory in order to execute the ls or the cd command.

How to change permissions?

Use the chmod (change mode) command to change permissions.

There are two ways to use chmod:

The symbolic mode
The absolute mode

Symbolic mode

With symbolic permissions we can add, delete, or specify the permission set we want by using the operators

+ : Adds the designated permission(s) to a file or directory

- : Removes the designated permission(s) from a file or directory

= : Sets the designated permission(s)

a) Change permission for other users

chmod o+wx test1file

b) Change permission for owner user

chmod u-x testfile

c) Change permission for group

chmod g=rx testfile

d) Change permission for users and groups

chmod o+wx,u-x,g=rx testfile

Absolute Mode

Use a number to specify each set of permissions for the file

Number	Description	Detail
0	No permission	---
1	Execute permission	--x
2	Write permission	-w-
3	Execute and write permission: 1 (execute) + 2 (write) = 3	-wx
4	Read permission	r--
5	Read and execute permission: 4 (read) + 1 (execute) = 5	r-x
6	Read and write permission: 4 (read) + 2 (write) = 6	rw-
7	All permissions: 4 (read) + 2 (write) + 1 (execute) = 7	rwx

Examples

a) chmod 755 testfile (all, read-write, read-write)

b) chmod 743 testfile (all, read,write-execute)

c) chmod 043 testfile (no permission, read, write-execute)

More details about the file and directory are explained with examples in the video below:

Tuesday, August 7, 2018

Monday, August 6, 2018

Important and Useful Unix commands

Are you looking for an article which provides a list of important commands used for daily unix activities? This article provides a consolidated list of unix commands.

Introduction

In this article we have listed unix commands for : File and Directories, Compressed Files and Manipulating Data

File and Directory

Command	Details
cat	Displays File Contents
cd	Changes Directory to another directory
chgrp	Changes file group
chmod	Changes permissions
cp	Copies source file into destination
file	Determines file type
find	Finds files
grep	Searches files for regular expressions
head	Displays first few lines of a file
ln	Creates softlink on oldname
ls	Displays information about file type
mkdir	Creates a new directory dirname
more	Displays data in paginated form
mv	Moves (Renames) an oldname to newname
pwd	Prints current working directory
rm	Removes (Deletes) filename
rmdir	Deletes an existing directory provided it is empty
tail	Prints last few lines in a file
touch	Updates access and modification time of a file
vi	To view file content

Compressed Files

Command	Details
compress	Compresses files
gunzip	Helps uncompress gzipped files
gzip	GNU alternative compression method
uncompress	Helps uncompress files
unzip	List, test and extract compressed files in a ZIP archive
zcat	Cat a compressed file
zcmp	Compares compressed files
zdiff	Compares compressed files
zmore	File perusal filter for crt viewing of compressed text
apropos	Locates commands by keyword lookup
info	Displays command information pages online
man	Displays manual pages online
whatis	Searches the whatis database for complete words
yelp	GNOME help viewer

Manipulating Data

Command	Details
awk	Pattern scanning and processing language
cmp	Compares the contents of two files
comm	Compares sorted data
cut	Cuts out selected fields of each line of a file
diff	Differential file comparator
expand	Expands tabs to spaces
join	Joins files on some common field
perl	Data manipulation language
sed	Stream text editor
sort	Sorts file data
split	Splits file into smaller files
tr	Translates characters
uniq	Reports repeated lines in a file
wc	Counts words, lines, and characters
vi	Opens vi text editor
vim	Opens vim text editor
fmt	Simple text formatter
spell	Checks text for spelling error
ispell	Checks text for spelling error
emacs	GNU project Emacs
ex, edit	Line editor

The video below provides a tutorial on Unix topics -

Technology World

DronaBlog

Tuesday, August 14, 2018

Java Interview Questions and Answers - Part I

Thursday, August 9, 2018

Important File and Directory permissions in Unix

What are the types of file permissions?

How to display Permissions?

Understanding File access modes

Understanding Directory access mode

How to change permissions?

Symbolic mode

Absolute Mode

Examples

Wednesday, August 8, 2018

Informatica Master Data Management - MDM - Quiz - 4

Sample SOAP UI Request and Response for RecalculateBO and RecalculateBVT

Sample executeBatchRecalculateBo request

Sample executeBatchRecalculateBo response

Sample executeBatchRecalculateBvt request

Sample executeBatchRecalculateBvt response