Design Patterns: Factory Method Pattern 5:34 AM

/**
* A simple implementation of Factory Method Pattern
* using a real time CricketPlayer example
*/


//Base
public interface CricketPlayer{
    public String play();
}


//Subclass
class Bowler implements CricketPlayer{
    public String  play (){
        return "takes a wicket";
    }
}


//Subclass
class Batsman implements CricketPlayer{
    public String  play (){
        return "hits a six";
    }
}


//Factory class - contains the logic of instatiating players
public class CricketPlayerFactory{
    CricketPlayer player;
   
    public CricketPlayer getPlayerWho(String does){
        if(does.equals("bats"))
            player = new Batsman();
        else if(does.equals("bowls"))
            player = new Bowler();
        return player;              
    }
}


//Factory method implementation
public class FactoryImplementation{
    public static void main(String args){
        //create a factory
        CricketPlayerFactory factory = new CricketPlayerFactory();
        //ask factory to instantiate the player
        CricketPlayer player = factory.getPlayerWho("bats");
        //use the player
        System.out.prinln(player. play ());
    }
}

Tweet

Design Patterns: Singleton Pattern 5:10 AM

/**
* A simple Implementation of a singleton
*/
class MySingleton{
   
    static MySingleton singletonInstance;
   
   //****** instantiation ******


    static MySingleton getInstance(){
        if(singletonInstance == null)
            singletonInstance = new MySingleton();
        return singletonInstance;
    }
   
    private MySingleton(){
        //cannot be called public with new
    }


   //****** logic ******   
    ....
    ....
}


MySingleton.getInstance();


FYI, Points to remember

• Singletons are bad. 
• They are just glorified statics and hence against OOP principles. 
• They should be rarely used. A classic example: for logging purposes.
• Singletons are hard to unit test.
• Also bad because it is NEVER a good practice to mix instantiation and logic in a single class. 

Tweet

Why Groovy over java? 5:12 AM

Some reasons why java developers should consider adapting groovy.

Groovy is married to java 

Groovy's seamless integration with java makes it possible to use all frameworks and libraries available for java, without any hassles regarding language compatibility. Groovy is so much compatible with java that one can merely change the .java extension to .groovy and run it. After all, groovy is just dynamic java with some add-ons and wrappers.

Dynamic typing

Unlike java, groovy does not throw compilation errors on your face. One of the biggest pleasure when compared to java, groovy doesn't impose explicit type casting which is a pain in the butt while programming in java. Groovy is a programmer friendly language and doesn't go out of control as long as the programmer is sure about his own code. It also supports optional typing, the native java syntax can be retained. 

Blocks and closures 

One of the best aspects of groovy is that it provides higher level constructs like blocks and closures found in languages like Smalltalk and Ruby. Block closures are handy powerful features which java lacks.

//To extract the first letter out of each element of a list.
def words = ['animal', 'bird' , 'cat', 'fly', 'dog']

def letters = words.collect{ it[0] }
println letters

//easy iterations

words.eachWithIndex{ word, index ->

    println "$word at $index"

}

The list goes on. Further refer : find{}, findAll{}, sort{}, each{}, contains{} et als, all of which make programming a breeze. 

Reflection in hand

As in smalltalk, Groovy has a concept of metaclass while initializing objects. This metaClass provides wrappers around the native Reflection API of java which enable the programmer to change the behavior of a class at run time.

For example : When compared to java, inspecting the methods of a class at runtime is as simple as :

class Test{

def one = 1

    def getOne(){

        return one

    }

}

println Test.metaClass.methods //prints getOne() and all methods default methods of the class.

Likewise to inspect the properties of a class at runtime, 

println Test.metaClass.properties //prints one and other properties if any

Likewise, injecting a method called getTwo() is as simple as :

Test.metaClass.getTwo = { return 2 }

Sugar Syntax

Besides addition of new language constructs, Perhaps this is one other aspect of groovy which hugely differentiates it with java.

Here I display two good examples that would make groovy an obvious win w.r.t to its sugar syntax.

ex: 1) A program to fetch the contents of a file in java would add up to around 10 - 15 lines. In groovy :

new File('C:\Temp\input.txt').getText()

Or further more, Parsing it is as simple as

new File('C:\Temp\input.txt').eachLine{ line ->

 //parsing logic

}

ex: 2) Given a url, to read the contents of a webpage, in java there is all this crap of opening streams, buffered readers and piping the contents, handling the exceptions etc. In groovy it is as simple as

'http://nerdysermons.blogspot.in'.toUrl().text

Further more...

Groovy has excellent wrappers around basic java functionalities. For example: With SwingBuilder, building swing UIs becomes darn simple.

For example: To built a swing application with a click me button and text area that prints hello message upon button click, a java program for the same would extend to more around 30 - 40 lines of code with initialization, building UIs, writing an actionListener etc. In groovy, this four liner script would suffice. 

new groovy.swing.SwingBuilder().edt{

    frame(show:true, size:[200,270]){

    panel(){

        button(label:'Click Me', actionPerformed :{ta.setText('Hello')})

        ta = textArea(columns:20, rows : 10)

        }

    }

}

Another great feature of groovy is its ability to build, create and parse XMLs with its XmlParser and XmlSlurper facilties. Some other include inbuilt assertions, GPath expressions,    String interpolations, etc.

I can go on like this for some time. This post is an introduction to depict groovy goodness comparing it to java which is strict and verbose. The more emphasis w.r.t the groovy vs java argument is on writing less code which possesses the java-ish flavor but is a lot elegant.

Tweet

Redirecting log4j and Print streams to Custom Console 4:23 AM

This is a custom JTextArea that I've coded for that can redirect and display all the print streams onto it including apache's log4j statements.



class MyConsole {
static outArea, consoleScroll, consoleTab

static log = Logger.getLogger(MyConsole.class)

//redirect the current println and err streams onto custom Stream 

static setUpStreams(){
outArea = JTextArea(10,100)
System.setErr(new PrintStream(new MyStream(outArea)));
System.setOut(new PrintStream(new  MyStream (outArea)));
WriterAppender logAppender = new WriterAppender(new PatternLayout(), new    MyStream (outArea));

Logger.getRootLogger().addAppender(logAppender);
}

public MyConsole(){ 
      setUpStreams()
}

}

//custom stream to which the standard streams are redirected
public class  MyStream  extends OutputStream {
JTextArea ta;
def str = ''
def buffer = []

MyStream (JTextArea t) {
super();
ta = t;
}

//detects \n and stores the line in a buffer and then prints the whole line..

public synchronized void write(int i) {

buffer.add(Character.toString((char)i))
if(buffer.last()=='\n'){
buffer.each{
str = str + Character.toString((char)it);
}
ta.append(str)
str = ''
buffer.clear()
}

//ta.append(Character.toString((char)i));

}

public synchronized void write(char[] buf, int off, int len) {
String s = new String(buf, off, len);
ta.append(s);

}
}



PS : I tried to keep the java-ish syntax alive in the snippet. Albeit that I guess I might have resorted to groovy's sugar syntax in a couple of places. Please make the changes accordingly. 

Tweet

Groovy Based RSS Reader - Intro 3:47 AM

A desktop application with the help of which a user can keep track of his favorite blogs or the frequently visited websites.

Pre-requisite to be able to work with:
The website/blog should necessarily have an option for RSS feed subscription.

Rough Ideas/Steps involved :

1) Fetch the URL of the website/blog from the user as input.

2) Search the metatags of the page for existence of an rss feed.

3) If an rss feed for the website/blog exists, fetch the rss content from the feed URL, parse it and perform the display logic.

4) On exit, save state of UI i.e of all the blogs subscribed. On reopen, update feeds.

Genuinely started with the aim to target bloggers i.e users of blogspot/wordpress and other famous blog hosting sites. Should be in a position to extend the functionality to all websites that provide for an RSS subscription.

Tweet

Build a Binary Tree & Perform an Inorder traversal 1:46 AM

/*
* A simple groovy implementation to create a Binary Tree
* and to perform inorder traversal
*/

class Node{

    Node left, right
    int data
   
    Node(data){
        this.data = data
        left = null
        right = null
    }
}


class BTree{

    static def insert(Node node, val){
      if(val < node.data){
          if(node.left == null){
              node.left = new Node(val)
              println "inserting $val to the left of $node.data"
          }
         
          else insert(node.left, val)
      }
     
      else if(val > node.data){
          if(node.right == null){
              node.right = new Node(val)
              println "inserting $val to the right of $node.data"
          }
         
          else insert(node.right, val)
      }
     
    }
   
    //left, root, right
    static def printInOrder(Node node){
        if(node == null) return
       
        else{
            printInOrder(node.left)
            println node.data
            printInOrder(node.right)
        }
    }
}

//Shift to main if you aren't running this as a groovy script
def root = new Node(25)
BTree.insert(root, 10)
BTree.insert(root, 30)
BTree.insert(root, 24)
BTree.insert(root, 299)
BTree.insert(root, 266)
BTree.insert(root, 121)
BTree.insert(root, 920)

//Inorder traversal of the entered elements
BTree.printInOrder(root)

Tweet