Java support more than 18 international languages so java take 2 byte for characters, because for 18 international language 1 byte of memory is not sufficient for storing all characters and symbols present in 18 languages. Java supports Unicode but c support ascii code. In ascii code only English language are present, so for storing all English latter and symbols 1 byte is sufficient.
What is java and
javac ?
.Java tool are
used for run the java program and javac tool are used for compile the java
program.
Why Boolean data
types take zero byte of memory ?
Boolean data type
takes zero bytes of main memory space because Boolean data type of java
implemented by Sun Micro System with a concept of flip - flop. A flip - flop is
a general purpose register which stores one bit of information (one true and
zero false).
Which access
specifier are called universal access specifier ?
Public
Which access
specifier is not a keyword ?
Default
Which access specifier is package level access specifier ?
Which access specifier is package level access specifier ?
Default
Type Casting
Assigning a value
of one type to a variable of another type is known as Type Casting.
Example :
int x = 10;
byte y = (byte)x;
In Java, type
casting is classified into two types,
Widening
Casting(Implicit)
Narrowing
Casting(Explicitly done)
Widening or
Automatic type converion
Automatic Type casting
take place when,
è
the two
types are compatible
è
the
target type is larger than the source type
Narrowing or
Explicit type conversion
When you are
assigning a larger type value to a variable of smaller type, then you need to
perform explicit type casting.
What is the
difference between Method and Constructor
·
Method
can be any user defined name
Constructor
must be class name
·
Method
should have return type
Constructor
should not have any return type (even void)
·
Method
should be called explicitly either with object reference or class reference.
Constructor
will be called automatically whenever object is created
·
Method
is not provided by compiler in any case.
The
java compiler provides a default constructor if we do not have any constructor.
Important points
For Exception Handling:
1. If you do not explicitly use the try catch
blocks in your program, java will provide a default exception handler, which
will print the exception details on the terminal, whenever exception occurs.
2. Super class Throwable overrides toString()
function, to display error message in form of string.
3. While using multiple catch block, always
make sure that exception subclasses comes before any of their super classes.
Else you will get compile time error.
4. In nested try catch, the inner try block,
uses its own catch block as well as catch block of the outer try, if required.
5. Only the object of Throwable class or its
subclasses can be thrown.
NullPointerException
Trying to access
a null object or performing operations on an object having a null value.
1. package com.beingjavaguys.core;
2. import java.util.ArrayList;
3.
4. public class ExceptionTest {
5.
6. public static void main(String[] args)
{
7. String string = null;
8. System.out.println(string.length());
9. }
10. }
11.
Exception in
thread "main" java.lang.NullPointerException
at
com.beingjavaguys.core.ExceptionTest.main(ExceptionTest.java:9)
Explain what is Maven? How does it work?
Maven is a
project management tool. It provides the developer a complete build lifecycle
framework. On executing Maven commands, it will look for POM file in Maven; it
will run the command on the resources described in the POM.
List out what are
the aspects does Maven Manages?
Maven handles
following activities of a developer
• Build
• Documentation
• Reporting
• Dependencies
• SCMs
• Releases
• Distribution
• Mailing list
Mention the three
build lifecycle of Maven?
• Clean: Cleans
up artifacts that are created by prior builds
• Default
(build): Used to create the application
•
Site: For the project generates site documentation
Explain what is
POM?
In Maven, POM
(Project Object Model) is the fundamental unit of work. It is an XML file which
holds the information about the project and configuration details used to build
a project by Maven.
Explain what is
Maven artifact?
Usually an
artifact is a JAR file which gets arrayed to a Maven repository. One or more
artifacts a maven build produces such as compiled JAR and a sources JAR.
Each
artifact includes a group ID, an artifact ID and a version string.
Explain what is
Maven Repository? What are their types?
A Maven
repository is a location where all the project jars, library jars, plugins or
any other particular project related artifacts are stored and can be easily
used by Maven.
Their
types are local, central and remote
Why Maven Plugins
are used?
Maven plugins are
used to
• Create a jar
file
• Create war file
• Compile code
files
• Unit testing of
code
• Documenting
projects
• Reporting
List out the
dependency scope in Maven?
The various
dependency scope used in Maven are:
• Compile: It is
the default scope, and it indicates what dependency is available in the
classpath of the project
• Provided: It
indicates that the dependency is provided by JDK or web server or container at
runtime
• Runtime: This
tells that the dependency is not needed for compilation but is required during
execution
• Test: It says
dependency is available only for the test compilation and execution phases
• System: It
indicates you have to provide the system path
• Import: This
indicates that the identified or specified POM should be replaced with the
dependencies in that POM’s section
Mention how
profiles are specified in Maven?
Profiles are
specified in Maven by using a subset of the elements existing in the POM
itself.
Explain how you
can exclude dependency?
By
using the exclusion element, dependency can be excluded
Mention the
difference between Apache Ant and Maven?
• Ant is a
toolbox – Maven is a framework
• Ant does not
have formal conventions like project directory structure – Maven has
conventions
• Ant is
procedural; you have to tell to compile, copy and compress – Maven is
declarative ( information on what to make & how to build)
• Ant does not
have lifecycle; you have to add sequence of tasks manually – Maven has a
lifecycle
• Ant scripts are
not reusable – Maven plugins are reusable
In Maven what are
the two setting files called and what are their location?
In Maven, the
setting files are called settings.xml, and the two setting files are located at
• Maven
installation directory: $M2_Home/conf/settings.xml
• User’s home
directory: ${ user.home }/ .m2 / settings.xml
List out what are
the build phases in Maven?
Build phases in
Maven are
• Validate
• Compile
• Test
• Package
• Install
•
Deploy
List out the
build, source and test source directory for POM in Maven?
• Build = Target
• Source =
src/main/java
• Test =
src/main/test
Where do you find
the class files when you compile a Maven project?
You
will find the class files ${basedir}/target/classes/.
Explain what
would the “jar: jar” goal do?
jar: jar will not
recompile sources; it will imply just create a JAR from the target/classes
directory considering that everything else has been done
List out what are
the Maven’s order of inheritance?
The maven’s order
of inheritance is
• Parent Pom
• Project Pom
• Settings
• CLI parameters
For POM what are
the minimum required elements?
The
minimum required elements for POM are project root, modelVersion, groupID,
artifactID and version
Explain how you
can produce execution debug output or error messages?
To produce
execution debug output you could call Maven with X parameter or e parameter
Explain how to
run test classes in Maven?
To run test
classes in Maven, you need surefire plugin, check and configure your settings
in setting.xml and pom.xml for a property named “test.”
What is
archetype?
Archetype is the
maven plugin. It creates the project structure.
What would the
command mvn clean do ?
This command
removes the target directory with all the build data before starting the build
process.
What is Central
Repository?
It
is repository provided by Maven community. It contains a large number of commonly
used libraries. When Maven does not find any dependency in local repository, it
starts searching in central repository using following URL:
http://repo1.maven.org/maven2/.
What is local
repository?
Maven local
repository is a folder location on your machine. It gets created when you run
any maven command for the first time. Maven local repository keeps your
project's all dependencies (library jars, plugin jars etc).
What is Remote
Repository?
Sometimes, Maven
does not find a mentioned dependency in central repository as well then it
stops the build process and output error message to console. To prevent such
situation, Maven provides concept of Remote Repository which is developer's own
custom repository containing required libraries or other project jars.
What is the
sequence in which Maven searches for dependency libraries?
Following is the
search pattern −
Step 1 − Search
dependency in local repository, if not found, move to step 2 else if found then
do the further processing.
Step 2 − Search
dependency in central repository, if not found and remote
repository/repositories is/are mentioned then move to step 4 else if found,
then it is downloaded to local repository for future reference.
Step 3 − If a
remote repository has not been mentioned, Maven simply stops the processing and
throws error (Unable to find dependency).
Step 4 − Search
dependency in remote repository or repositories, if found then it is downloaded
to local repository for future reference otherwise Maven as expected stop
processing and throws error (Unable to find dependency).
What is SNAPSHOT
in Maven?
SNAPSHOT is a
special version that indicates a current development copy. Unlike regular
versions, Maven checks for a new SNAPSHOT version in a remote repository for
every build.
What is
difference between Snapshot and Version?
In case of
Version, if Maven once downloaded the mentioned version say data-service:1.0,
it will never try to download a newer 1.0 available in repository. To download
the updated code, data-service version is be upgraded to 1.1.
In case of
SNAPSHOT, Maven will automatically fetch the latest SNAPSHOT
(data-service:1.0-SNAPSHOT) everytime app-ui team build their project.
What is a Mojo?
A mojo is a Maven
plain Old Java Object. Each mojo is an executable goal in Maven, and a plugin
is a distribution of one or more related mojos.
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