Shantibhushan Naik

Tag: new

  • Farewell 2012 and welcome 2013

    We had a nice time with one on my old friends – Yogesh, and his family. Enjoyed a memorable time with his daughter Yukta, and enjoyed delicious ‘parathas’ by his wife Hema. After a hearty chat, we bid farewell to 2012 over a sumptuous Indian dinner at Swagat, Roppongi.

  • Happy New Year 2011 Wishes

    Happy new Year 2011

    I wish ALL of you a very Happy & Prosperous New Year 2011 !

  • Happy New Year 2011 – Wishes to my wife

    My best wishes, and sincere feelings for my wife Elena, expressed as a little poem.

  • Nicolas performing You should be dancing tonight

    Hilarious, isn't it?

  • Spring and Logback

    IoC, or DI definitely takes a perspective turnaround inside your head, but you get around it slowly.  I was playing around ways to integrate LogBack, and Spring – essentially around having Spring give me a pre-created instance of LogBack logger.

    I searched around posts, but most people seem to be against using Spring just for substituting one-line of Logback (Logger log = LoggerFactory.getLogger("LogbackTest");) to get your logger.

    I, on the other hand, was more interested in how to get Spring give me a LogBack logger instance without too much contrived hand-written code to achieve so. And with a bit of reading through Spring principles, documentation I found the way.

    Essentially, when using Logback’s LoggerFactory you have access to only a single getLogger() factory method. This is static which makes things a bit different for what Spring would call a bean – a class providing constructor, getter, setter methods. To circumvent this non-bean style, Spring provides what you call as static initializers a.k.a substitutes for constructors, which allow you to call a static method in lieu of calling a constructor on an object.

    <?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN"
 "http://www.springframework.org/dtd/spring-beans.dtd">

<beans>
 <bean id="bean1" class="org.slf4j.LoggerFactory" factory-method="getLogger">
 <constructor-arg value="LogbackTest" />
 </bean>
</beans>

    Now, this bean1 can be used as a regular bean inside your class

    ApplicationContext ctx = new FileSystemXmlApplicationContext("logbacktest.xml");
 Logger log = (Logger) ctx.getBean("bean1");

 log.debug("This is my first message");
 log.info("How about this information message");

    Throw in a logback.xml in your classpath, and viola you have a nice Spring injected dependency – log in your code, while still using Logback!

  • Racking brains – a Javascript string combination generator

    After racking my brains for almost 4 days (yeah I am a slow learner) I finally created a simple Javascript string combination generator

    See the demo http://naiksblog.info/stringcombinations.html

    I tried modeling the logic to how databases combine sets in a cross join. All rows from left side are combined with all rows from right side.

    The script is as below

    	function combine(a, b) {
		var r= new Array();
		for(var i= 0, k= 0; i < a.length; i++) {
			for(var j= 0; j < b.length; j++) {
				if(-1==a[i].indexOf(b[j])) r[k++]= a[i]+ b[j];
			}
		}

		return(r);
	}

    You can call this as below

    	function permute() {
		var a= "abcd";
		var p= new Array();

		for(var i= 0; i< a.length; i++) p[i]= a.charAt(i);
		var r= p;	// Input string as-is is first permutation
		for(var i= 1; i< a.length; i++) r= combine(r, p);	// Get the permutations
		// r.length - Get the combinations
		// r contains all combinations as an array
	}

    Some points worth noting

    • If any character is repeated, the combination does not happen successfully since the logic tries to remove same character matching elsewhere
    • The number of combinations increase by factorial of the number of characters, hence it will be a good idea to perform this on server side ideally otherwise javascript will hang for large strings
    • Logic could be optimized to generate combination in a different better way than using crossjoin strategy

  • Extremely useful tips for Java

    1. A .java class can contain only one top-level public class.  All other top level classes in same .java file cannot be private or protected or public, only default (package-level access) is allowed.
    2. If no package is specified for class, it belongs to unnamed package – which cannot be imported.
    3. Unlike Linux utilities, long parameters or short parameters to java(c) need just a space before parameter value. e.g. -classpath <classpath> or -cp <classpath> are same. There is no -classpath=<classpath> syntax in java(c) command line.
    4. 8 primitive types (byte, short, int, long, float, double, char, boolean), special type void, and base type for all objects – java.lang.Object.
    5. null is not a keyword, type. It is a value.
    6. String objects created using short-hand String A= "a string";
      syntax creates Strings on pool in heap. A is pointer (32-bit to max. 64-bit) to a String object “a string” on heap memory allocated to your program. Using short-hand syntax to “a string” on String B= "a string"; will point to same string object on heap.
    7. Object gets garbage-collected, not it’s reference.
    8. Garbage collection is indeterminate. You cannot guarantee freeing of memory by forcing System.gc()
    9. finalize method is invoked only once before being removed from memory. Always call super.finalize() if you override it.
    10. Parameters (primitive, references) are always passed-by-value. There is no pass-by-reference in Java. The references passed can be used to modify the object the reference points, but not the reference itself is not modified.
    11. Return values from function are also passed by value, never by reference.
    12. Compound operators (+=, -=, *= etc) automatically cast. Compiler never throws any error on data mismatch.
    13. & (and) results in 1 if both are 1, | (or) results in 0 if both are 0, ^ (xor) results in 1 if either operand is 1
    14. char supports increment, decrement operators.
    15. The default isequal() implementation of Object tests for reference equality, which is same as ==.
    16. When using operators, Java automatically promotes values to int or higher. For values below int – byte, short – an explicit cast is required.
    17. extends comes first then implements
    18. Java tokenizes your source into separators (tab or space), keywords, operators, literals, identifiers (variable names).
    19. new zeroes Object’s fields (instance variables), hence explicit initialization can be skipped.
    20. import static allows importing static variables like System.out into your program. Hence, you can simply use out without prefixing it with class name System.
    21. local variables must be initialized before using. Though method parameters are local variables too, since methods are called with parameters, they are initialized.
    22. arrays are fixed size data structures, where as collections are dynamically sized data structures.
    23. For multidimensional arrays, it is easier to imagine the first dimension as a single row containing the other dimensions.
    24. Array initialization always requires dimension to be provided when initializing through new (caught at compile time). If using array initializer, you can specify {} empty braces, but accessing any index at runtime will only result in index out of bounds exception.
    25. There is always a default constructor – empty body – available for your class only if you do not declare any constructor.
    26. super, this must be the first line in constructor. this() or super() both cannot be placed.
    27. Parent class constructor super() is always called. For this reason, you need to have an empty constructor always in parent class.
    28. Method signature is composed of method name and parameters. Modifiers, return type, exception list has nothing to do with it. Access-specifiers however control visibility.
    29. Javabean properties are get-, set- methods provided over a field in Javabean style.
    30. Variable length parameters always come at the end of the list, and they can be empty (meaning nothing was passed). Being at end of the list automatically implies that only variable length parameters is allowed. (Java 5.0)
    31. Overloading means providing different method signatures in same or inheriting class. Overriding means providing same return type, method signature in inheriting class.
    32. Covariant return types means overriding method returns a subclass of return type in parent class. (Java 5.0)
    33. Method hiding means overriding of static methods.
    34. Abstract method has no body. Interface methods are all abstract, while Abstract class can contain zero or more abstract methods.
    35. All abstract method of Interface are public, it’s fields are public, static and final. No static methods are allowed.
    36. Abstract method compiles with static modifier, but generates runtime error if directly accessed. If abstract static method is overridden in child class, child class works fine.
    37. Enum constructors are invoked for each element.
    38. Anonymous inner class can have only one instance. Local inner class can have multiple instances.
    39. Static nested class is similar to any top-level class.
    40. Static fields in class always need default value; otherwise code does not compile.
    41. false is boolean, 0 is not false, it is int zero
    42. switch…case does not allow case null, since a constant (and final) expression is required for case
    43. You can put break in default for switch
    44. enum classes can have main method
    45. for(;;) is a valid for-loop. It never finishes, since it is an infinite loop.
    46. In enhanced for loop, the variable used for iteration must be declared only in for loop, not outside it.
    47. Java complains if you have unreachable while loop code e.g while(false) is not allowed. However, contrarily if(false) is allowed!
    48. Variables declared inside do…while loop are not available in while to test for condition!
    49. It is a good idea to add labels to your loops to enhance readability
    50. Assertion is put in places in your code where you think it should be always true
    51. Though not a good design, but assertions do allow modification on variables while asserting them e.g. assert ++i
    52. try…catch – catch can never have an exception which is a subclass of previous catch clause. It throws compile error.
    53. Checked exceptions always derive from Exception, runtime exceptions derive from RuntimeException, errors derive from Error. Java enforces checked exceptions are either handled or thrown. For runtime, error there is no such rule, even if RuntimeException derives from Exception.
    54. try… must have either catch or finally atleast, otherwise compile gives error

  • https in 5 easy steps

    Simple 5 step guide to setting up https with your own self-signed certificate
    Prerequisites: Apache2, Ubuntu Server

    1. Generate local keypair
      /usr/bin/openssl genrsa -des3 -out {your domain name}.key 3072
    2. Create self-signed certificate
      /usr/bin/openssl req -new -key {your domain name}.key -x509 -out {your domain name}.crt
    3. Configure your host on port 443 to use the certificate
      <VirtualHost {your ip}:443>
      ...
      SSLEngine on
      SSLCertificateFile {path where certificate is}/{your domain name}.crt
      SSLCertificateKeyFile {path where key file is}/{your domain name}.key
      SetEnvIf User-Agent ".*MSIE.*" nokeepalive ssl-unclean-shutdown
      ...
      </VirtualHost>
    4. Optional: If you do not want to enter key password each you restart Apache, you can embed the password in key itself.
      /usr/bin/openssl rsa -in       {path where key file is}/{your domain name}.key -out {path where key file is}/{your domain name}.key.nopass
      Remember to update your Apache configuration to use the new file
      # SSLCertificateKeyFile {path where key fileis}/{your domain name}.key
      SSLCertificateKeyFile {path where key file is}/{your domain name}.key.nopass
    5. That’s it view it. Restart your apache to load the new configuration. And try accessing your url with https://

    If you receive a certificate warning, simply accept it, and proceed. Congratulations, your communication is now encrypted, and safe from prying eyes!

    Self-signed certificate

    [Translate]

  • Interesting alternatives to databases in opensource

    I stumbled upon this url. The list of various options on databases is pretty amazing.

    http://www.webresourcesdepot.com/25-alternative-open-source-databases-engines/

    It’s a definite read. I never knew so many existed.

  • Got my bike license – 大型二輪免許を一発合格しました

    Hurray ! I received my bike license today in Japan ! In my first attempt itself ! Wish me congratulations !

    Bike license in Japan
    My bike license in Japan

    Ok some background – I had a bike license from my country. I had not converted it to International License, so I had to opt only for conversion into Japanese license – 外国免許切り替え. I do have a car license obtained in Japan, so I was exempted from written test (which by the way is too difficult, trust me). Instead, I simply had to appear an actual driving test (which is again difficult, mind you). I was required to produce a translated copy of my original license from my country, which can be done in 30 mins in JAF offices. Rest are your passport (both old, new ones), an application form, few stamps which you can buy right there. I live in Tsukuba, so I had to goto Ibaragi License Center, which is situated in Mito. You can go during weekdays, from 09:00AM. Believe me, you better arrive early. There is plenty of crowd, for all sorts of licenses, and usually you have to spend almost whole day there, in case you pass the test and obtain the license. I spent close fo 6 hours today, but in the end I was a happy guy.

    Once they receive your application, they ask you few questions about your original license – How did you obtain it? Where did you practice? What kind of test did you appear for this license? How many cc bike? Learner’s license? etc. Unless there are any problems, you are then handed over a course map, and timings when your test will start. Mind you, the course map is given so that you “memorize” it, period. You are required to drive the exact course map, observing lane rules, traffic signs, signal, right or left indication, speed or slow. The usual advice is that you have some 45 mins in hand before your test starts. Thus, you should actually take the course map in hand, and walk the entire course by foot atleast once. I did that, making a mental note of the lanes, the distance around which I should turn on the indicator, and so on – till I burnt the course map into my brain cells !

    The most difficult are – Ipponbashi, and Slalom – for me. And I did literally walk on foot imagining I was on bike before my test started.

    I believe I was the only one appearing a bike test today – why I was alone sitting in the waiting room till my turn came. The instructor was kind enough to walk me (verbally) through the course map once again. He also gave me a brief about the bike – Honda CB750 – and for my own safety, in case I should fall, had me wear elbow, knee, body protector before the test.

    When the actual test started, the instructor actually sits in a watchtower, from which he had a complete view of the course. Once he gave a go, I just drove the same path I had walked on foot earlier. I was particularly careful about slow down sign, lane change, and making sure that I move my head from left to right wide enough to show that I am taking visual confirmations before proceeding. At one point when making a turn I did step down, but I guess that was OK, because if I’d had done the same on Ipponbashi or Slalom, or even S-letter, or Crank, I am out without any further discussion. Phew, I did feel once the bike will stop during Crank, but I was lucky enough to make it till the final stop.

    In the end, the instructor appraised my driving skills, and gave me the golden word – “合格” !