Java for the day

private methods on Interface

noreply@blogger.com (Unknown) — Wed, 21 Feb 2018 04:06:00 +0000

Private methods can be used on interface from java 9.
This will help in

Avoiding code duplication.
Ensuring code re-usability.
Improving code readability.

There is a possibility of writing common code on more than one default methods, which leads to code duplication. Introduction of private methods will avoid this code duplication.

Example: On java 8 - Default methods with duplication code.

In the below example, we can see common code is used on both the default methods M1 and M2.

public interface intra {

default void m1() {

//Business code for M1

// common code

}

default void m2() {

//Business code for M2

//common code

}

Example: From Java 9 - Default methods with Private method.

In the below example, Common code is extracted and added as a private method which can be called by default methods.

public interface intra {

default void m1() {

//Business code for M1

Common ();

}

default void m2() {

//Business code for M2

Common ();

}

private void common () {

//Common code

}

Cannot change version of project facet Dynamic Web Module to 2.5

noreply@blogger.com (Unknown) — Fri, 29 May 2015 15:46:00 +0000

Deselect the Dynamic Web Module in your project facets. Right click the Project -> preferences -> Project Facets
Then run Maven -> Update Project again.

Forgotten PostgreSQL Windows password

noreply@blogger.com (Unknown) — Mon, 18 May 2015 12:03:00 +0000

I have used net user postgres postgres to reset the password for my database but instead of a success message I am getting "System error 5 has occurred. Access is denied."

You've reset (or tried to reset) the service account password. PostgreSQL won't run as Administrator for security reasons and the installer generally sets it up with a "postgres" user account in PostgreSQL 9.1 and older¹. On Windows you can't start a service as a user without saving the password of the user in the registry, so that's what the installer does.

If you change the password for the Windows user account postgres, the PostgreSQL service can no longer start. So don't do that, you'll have to fix the service configuration to store the updated password.

Thankfully I think another mistake prevented you from doing that. It looks like you're probably running your command prompt without using "Run as Administrator" on an unprivileged Windows user account or a machine with UAC, so it isn't running with the access permissions required to change the password for the postgres user.

Before you try to change that password, make sure it's really what you want to do. What's the problem you're trying to solve here? Are you attempting to install a database update or something else that's asking for the password for the postgres Windows user?

Most likely you're just trying to log in to the database. For that, you use the (unfortunately completely unrelated) password stored in the database its self. Since you've lost/forgotten it you'll have to reset it:

Find your pg_hba.conf, usually in C:\Program Files\PostgreSQL\9.1\data\pg_hba.conf
If necessary, set the permissions on it so that you can modify it; your user account might not be able to do so until you use the security tab in the properties dialog to give yourself that right by using an admin override. Alternately, find notepad / notepad++ in your start menu, right click, choose "Run as administrator", then use File->Open to open pg_hba.conf that way.
Edit it to set the "host" line for user "postgres" on host "127.0.0.1/32" to "trust". You can add the line if it isn't there; just insert:
```
host all postgres 127.0.0.1/32 trust
```
before any other lines. (You can ignore comments, lines beginning with #).
Restart the PostgreSQL service from the Services control panel (start->run->services.msc)
connect using psql or PgAdmin-III or whatever you prefer
ALTER USER postgres PASSWORD 'postgres'
remove the line you added to pg_hba.conf or change it back
restart PostgreSQL again.

How to Create VirtualHost in Tomcat 7/8

noreply@blogger.com (Unknown) — Fri, 08 May 2015 06:39:00 +0000

Source : http://tecadmin.net/create-virtualhost-in-tomcat/

Why VirtualHost ?

Virtual Hosting provides us to host multiple domains (websites) on single server. It is an concept of resource sharing between multiple hosting account. The best use of Virtual hosting is shared hosting servers, where multiple users can host multiple websites on single server.

Setup Details:

We have created a Linux server with ip 192.168.1.100 for Tomcat hosting services only. Soinstall Tomcat 8 and configured to run on port 80. After than we have deployed two java web applications on tomcat using Tomcat Admin panel. Now both applications are running on following urls

http://192.168.1.100/myapp
http://192.168.1.100/myapp2

Now we want to run both web applications on main domains ( example.com & mydomain.org ). So that end users can access web application by using main domain name.

Create Virtual Hosts:

To create virtual hosts in Tomcat, first navigate to Tomcat installation directory and edit config/server.xml file in favorite editor. Add following host entries in configuration file.

 
<Host name="example.com"  appBase="webapps" unpackWARs="true" autoDeploy="true">
 www.example.com
 
 example_access_log

" suffix=".txt" pattern="%h %l %u %t "%r" %s %b" /> /opt/tomcat8/webapps/myapp" debug="0" reloadable="true"/> </Host> <Host name="mydomain.org" appBase="webapps" unpackWARs="true" autoDeploy="true"> www.mydomain.org mydomain_access_log" suffix=".txt" pattern="%h %l %u %t "%r" %s %b" /> /opt/tomcat8/webapps/myapp2" debug="0" reloadable="true"/> </Host>

Restart Tomcat Service

After adding virtualhost in Tomcat, we need to restart Tomcat service. Use tomcat init service to restart it or if you don’t have init service for tomcat, execute following commands from tomcat installation directory.

# ./bin/shutdown.sh
# ./bin/startup.sh

For killing a process linux

noreply@blogger.com (Unknown) — Tue, 05 May 2015 07:02:00 +0000

For killing a process that is associated with multiple processes, you need to kill that by using process id associated with that process.

To get the process id of that java process run

ps -A |grep java
output of this command will give the list of java processes running on your system. Note down Process ID (PID) of that process whom you want to kill and run

kill -9 PID

Generate Java objects from DTD or XML

noreply@blogger.com (Unknown) — Fri, 11 Apr 2014 10:10:00 +0000

On Jdk installed machine use this following Command to generate java classes.

1.    Create a folder. (say Test is the folder).

2.    Copy the DTD file in the location.

3.    On command prompt use the command

xjc -dtd -d com –p [Package structure] [Dtd file name with .dtd extention]

Java classes will be created inside test folder with the specified package structure.

UNIX Commands

noreply@blogger.com (Unknown) — Fri, 11 Apr 2014 09:27:00 +0000

Read write access
sudo chmod 777 /foldername/foldername

to provide access to jboss server
sudo chown jboss.jboss /foldername/foldername

To check how many instance is running
ps -ef | grep "java"

Delete all files
sudo rm -r ./*

Copy files from one folder to another
sudo cp -r /data/das/ /usr/local/jboss5/server/all-with-hornetq/

ln -s /webroot/home/httpd/test.com/index.php /home/vivek/index.php

Implementing Google charts on JSF Primefaces with dynamic data

noreply@blogger.com (Unknown) — Fri, 11 Apr 2014 01:11:00 +0000

Sample Code :

public class MapVO {
public MapVO(String country, String count) {
super();
this.country = country;
this.count = count;
}
private String country;
private String count;
public String getCountry() {
return country;
}
public void setCountry(String country) {
this.country = country;
}
public String getCount() {
return count;
}
public void setCount(String count) {
this.count = count;
}
}

import java.io.Serializable;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import javax.annotation.PostConstruct;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.SessionScoped;
@ManagedBean(name="mapBean")
@SessionScoped
public class MapBean implements Serializable{
/**
*
*/
private static final long serialVersionUID = 89459996582054769L;
private List<MapVO> mapList;
@PostConstruct
public void init() {
/* var data = google.visualization.arrayToDataTable([
['Country', 'Nos'],
['Germany', 200],
['United States', 300],
['Brazil', 400],
['Canada', 500],
['Japan', 600],
['China', 700]
]); */
// Instead of hardcoding data like below code, read data from database and create ArrayList like below.
mapList = new ArrayList<MapVO>();
mapList.add(new MapVO("JAPAN","200"));
mapList.add(new MapVO("China","100"));
mapList.add(new MapVO("Canada","1020"));
mapList.add(new MapVO("United States","1000"));
mapList.add(new MapVO("Germany","100"));
setMapList(mapList);
}
private HashMap<String, String> mapData;
public HashMap<String, String> getMapData() {
System.out.println("getMapData -- "+mapData.size());
return mapData;
}
public void setMapData(HashMap<String, String> mapData) {
System.out.println("setMapData -- "+mapData.size());
this.mapData = mapData;
}
public List<MapVO> getMapList() {
return mapList;
}
public void setMapList(List<MapVO> mapList) {
this.mapList = mapList;
}
}

Below is the sample xhtml file.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:h="http://java.sun.com/jsf/html"
xmlns:p="http://primefaces.org/ui"
xmlns:c="http://java.sun.com/jsp/jstl/core">
<h:head><title>PrimeFaces Test</title>
<script type='text/javascript' src='https://www.google.com/jsapi'></script>
<script type='text/javascript'>
google.load('visualization', '1', {'packages': ['geochart']});
google.setOnLoadCallback(drawRegionsMap);
function drawRegionsMap() {
var data = google.visualization.arrayToDataTable([
['Country', 'Nos'],
<c:forEach var="resultAnalysis" items="${mapBean.mapList}" >
['${resultAnalysis.country}',${resultAnalysis.count}],
</c:forEach>
]);
var options = {};
var chart = new google.visualization.GeoChart(document.getElementById('chart_div'));
chart.draw(data, options);
};
</script>
</h:head>
<h:body>
<div id="chart_div" style="width: 900px; height: 500px;"></div>
</h:body>
</html>

Output preview

Onblur change into upper case

noreply@blogger.com (Unknown) — Fri, 11 Apr 2014 00:31:00 +0000

We can use javaScript code to do this.

 

 function upperCaseApplInfo(compn){  
 compn.value=compn.value.toUpperCase().replace(/([^A-Z])/g,"");  
 }

Example: From input box in JSF, we can call the java script code as shown below.

 <h:inputtext onblur="upperCaseApplInfo(this);" value="#{formName.variableName}">  
 </h:inputtext>

Java heap space error in eclipse

noreply@blogger.com (Unknown) — Tue, 10 Aug 2010 15:06:00 +0000

Step 1: Create a shortcut for eclipse.exc

Step 2: Right click eclipse short cut and add target value with “-vm "C:\Program Files\Java\jre1.5.0_08\bin\javaw.exe" -vmargs -Xmx1024M -XX:MaxPermSize=512M”

Like “D:\eclipse.exe -vm "C:\Program Files\Java\jre1.5.0_08\bin\javaw.exe" -vmargs -Xmx1024M -XX:MaxPermSize=512M”

Step3 : start eclipse by clicking on the short cut created.

Transient access modifier in java

noreply@blogger.com (Unknown) — Tue, 07 Oct 2008 11:42:00 +0000

1. Transient can be applied only to class level variables.
2. Local variables can’t be declared as transient.
3. During serialization, Object’s transient variables are not serialized.
4. Transient variables may not be final or static. But the complies allows the declaration and no compile time error is generated.

Final access modifier in java

noreply@blogger.com (Unknown) — Tue, 07 Oct 2008 11:40:00 +0000

1. All the Variables, methods and classes can be declared as Final.
2. Classes declared as final class can’t be sub classed.
3. Method ‘s declared as final can’t be over ridden.
4. If a Variable is declared as final, the value contained in the Variable can’t be changed.
5. Static final variable must be assigned in to a value in static initialized block.

Final access modifier in java

noreply@blogger.com (Unknown) — Tue, 07 Oct 2008 11:40:00 +0000

String in java

noreply@blogger.com (Unknown) — Fri, 12 Sep 2008 09:08:00 +0000

String is Immutable and String Is a final class. The String class provides for strings whose value will not change.
One accessor method that you can use with both strings and string buffers is the length() method, which returns the number of characters contained in the string or the string buffer.

The methods in String Class:-
toString( )
equals( )
indexOff( )
LowerCase( )
charAt( )
compareTo( )
lastIndexOff( )
UpperCase( )
getChars( )
subString( )
trim( )
getBytes( )
concat( )
valueOf( )
toCharArray( )
replace( )

Data Encapsulation in JAVA

noreply@blogger.com (Unknown) — Tue, 09 Sep 2008 07:35:00 +0000

What is data encapsulation?
The most common example I can think of is a javabean. Encapsulation may be used by creating 'get' and 'set' methods in a class which are used to access the fields of the object. Typically the fields are made private while the get and set methods are public.
Encapsulation can be used to validate the data that is to be stored, to do calculations on data that is stored in a field or fields, or for use in introspection (often the case when using javabeans in Struts, for instance).

Garbage Collection in Java

noreply@blogger.com (Unknown) — Wed, 27 Aug 2008 09:50:00 +0000

When an object is no longer referred to by any variable, java automatically reclaims memory used by that object. This is known as garbage collection.System.gc() method may be used to call it explicitly and does not force the garbage collection but only suggests that the JVM may make an effort to do the Garbage Collection.

Garbage Collection in Java

noreply@blogger.com (Unknown) — Wed, 27 Aug 2008 09:50:00 +0000

Static in JAVA

noreply@blogger.com (Unknown) — Mon, 25 Aug 2008 11:18:00 +0000

access modifier. Signa: Variable-Static int b; Method- static void meth(int x)

1. When a member is declared as Static, it can be accessed before any objects of its class
are created and without reference to any object. Eg : main(),it must call before any object exit.

2. Static can be applied to Inner classes, Variables and Methods.

3. Local variables can’t be declared as static.

4. A static method can access only static Variables. and they can’t refer to this or super in any way.

5. Static methods can’t be abstract.

6. A static method may be called without creating any instance of the class.

7. Only one instance of static variable will exit any amount of class instances.

Constructor in Java

noreply@blogger.com (Unknown) — Wed, 20 Aug 2008 08:41:00 +0000

1. A constructor method is special kind of method that determines how an object is initialized when created.

2. Constructor has the same name as class name.

3. Constructor does not have return type.

4. Constructor cannot be over ridden and can be over loaded.

5. Default constructor is automatically generated by compiler if class does not have once.

6. If explicit constructor is there in the class the default constructor is not generated.

7. If a sub class has a default constructor and super class has explicit constructor the code will not compile.

What are access specifiers and access modifiers ?

noreply@blogger.com (Unknown) — Wed, 20 Aug 2008 08:36:00 +0000

Accesss specifiers Access modifiers
Public Public
Protected Abstract
Private Final
Static
Volatile Constant
Synchronized
Transient
Native

Interfaces in Java

noreply@blogger.com (Unknown) — Wed, 20 Aug 2008 08:31:00 +0000

Interfaces can be used to implement the Inheritance relationship between the non-related classes that do not belongs to the same hierarchy, i.e. any Class and any where in hierarchy. Using Interface, you can specify what a class must do but not how it does.

1. A class can implement more than one Interface.

2. An Interface can extend one or more interfaces, by using the keyword extends.

3. All the data members in the interface are public, static and Final by default.

4. An Interface method can have only Public, default and Abstract modifiers.

5. An Interface is loaded in memory only when it is needed for the first time.

6. A Class, which implements an Interface, needs to provide the implementation of all the methods in that Interface.

7. If the Implementation for all the methods declared in the Interface are not provided , the class itself has to declare abstract, other wise the Class will not compile.

8. If a class Implements two interface and both the Intfs have identical method declaration, it is totally valid.

9. If a class implements two interfaces both have identical method name and argument list, but different return types, the code will not compile.

10. An Interface can’t be instantiated. Intf Are designed to support dynamic method resolution at run time.

11. An interface can not be native, static, synchronize, final, protected or private.

12. The Interface fields can’t be Private or Protected.

13. A Transient variables and Volatile variables can not be members of Interface.

14. The extends keyword should not used after the Implements keyword, the Extends must always come before the Implements keyword.

15. A top level Interface can not be declared as static or final.

16. If an Interface species an exception list for a method, then the class implementing the interface need not declare the method with the exception list.

17. If an Interface can’t specify an exception list for a method, the class can’t throw an exception.

18 If an Interface does not specify the exception list for a method, he class can not throw any exception list.

------------------------------------------------
The general form of Interface is
Access interface name {
return-type method-name1(parameter-list);
type final-varname1=value;
}
-------------------------------------------------
Marker Interfaces : Serializable, Clonable, Remote, EventListener,

Java.lang is the Package of all classes and is automatically imported into all Java Program
Interfaces: Clonable , Comparable, Runnable

Declaration of access specifier and access modifiers

noreply@blogger.com (Unknown) — Wed, 20 Aug 2008 08:29:00 +0000

Class - Public, Abstract, Final
Inner Class - Public, Protected, Private, Final, Static,
Anonymous - Public, Protected, Private, Static
Variable - Public, Protected, Private, Final, Static, Transient, Volatile, Native
Method - Public, Protected, Private, Final, Abstract, Static, Native, Synchronized
Constructor - Public, Protected, Private
Free-floating code block - Static, Synchronized

Oops Concepts in java

noreply@blogger.com (Unknown) — Wed, 20 Aug 2008 05:27:00 +0000

Abstraction: Showing the essential and hiding the non-Essential is known as Abstraction.

Encapsulation: The Wrapping up of data and functions into a single unit is known as Encapsulation. Encapsulation is the term given to the process of hiding the implementation details of the object. Once an object is encapsulated, its implementation details are not immediately accessible any more. Instead they are packaged and are only indirectly accessed via the interface of the object.

Inheritance: is the Process by which the Obj of one class acquires the properties of Obj’s another Class. A reference variable of a Super Class can be assign to any Sub class derived from the Super class. Inheritance is the method of creating the new class based on already existing class , the new class derived is called Sub class which has all the features of existing class and its own, i.e sub class.Adv: Reusability of code , accessibility of variables and methods of the Base class by the Derived class.

Polymorphism: The ability to take more that one form, it supports Method Overloading & Method Overriding.

Method overloading: When a method in a class having the same method name with different arguments (diff Parameters or Signatures) is said to be Method Overloading. This is Compile time Polymorphism. Using one identifier to refer to multiple items in the same scope.

Method Overriding: When a method in a Class having same method name with same arguments is said to be Method overriding. This is Run time Polymorphism.o Providing a different implementation of a method in a subclass of the class that originally defined the method.

1. In Over loading there is a relationship between the methods available in the same class ,where as in Over riding there is relationship between the Super class method and Sub class method.

2. Overloading does not block the Inheritance from the Super class , Where as in Overriding blocks Inheritance from the Super Class.

3. In Overloading separate methods share the same name, where as in Overriding Sub class method replaces the Super Class.

4. Overloading must have different method Signatures , Where as Overriding methods must have same Signatures.

Dynamic dispatch: is a mechanism by which a call to Overridden function is resolved at runtime rather than at Compile time , and this is how Java implements Run time Polymorphism.

Dynamic Binding: Means the code associated with the given procedure call is not known until the time of call the call at run time. (it is associated with Inheritance & Polymorphism).

Program to generate 10 Random nos

noreply@blogger.com (Unknown) — Tue, 19 Aug 2008 08:36:00 +0000

/*Write a program to generate 10 Random nos. between 1 to 100, and it

should not follow with decimal point.

*/

class RandomDemo{

public static void main(String args[]){

for(int i=1;i<=10;i++){

System.out.println((int)(Math.random()*100));

}

}

}

Java Hello World Program

noreply@blogger.com (Unknown) — Mon, 18 Aug 2008 06:46:00 +0000

Lets take a simple java program, we will write a program to display "Hello world"(as usual).

1. Open a notepad or text file, and start type the following coding.

2. Save this file with the name HelloWorld.java.
Tips: java file name and the class should always same - java compiler checks for this.
____________________________________________________________________
Code :
/** Comments * program to display "Hello world". */
class HelloWorld
{
public static void main (String args[])
{
System.out.println("Hello World!"); //Displays the enclosed String on the Screen Console
}
}
____________________________________________________________________

3. save this code under the path "C:\Program Files\Java\Jdk****\bin"
Note: **** It depends on java version installed in the system

4. open the command prompt, and get into the location C:\Program Files\Java\Jdk****\bin

5. Now Compile Java code.
From a command line, the command to compile this program is :
javac HelloWorld.java

6. Now run the program
java HelloWorld

You have written your first Java program! Congratulations :)