Hilarious, isn't it?
Tag: should
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Maintaining relationship – common friends
I was posed a very trivial question from one of my friends recently. It picked my interest, since I could not readily solve it, and I had the inkling that there is a better, simple solution for this problem.
The problem was, let’s say I have a table of users as below
And these users have friends as below
or more easier to read as 
Now, the trivial task was find common friends for users 1, and 5, hence naturally the answer should be
User 1 : Woody’s friends, and User 5 : Andy’s friends are
and 
So, the question I had was what could be the best SQL query that would be return me this result?
I thought of 2 different SQL queries
SELECT f.fid, u.name 'Woody and Andy\'s common friends' FROM
(SELECT f.`fid` FROM friends f
WHERE f.`uid` IN (1,5)
GROUP BY f.`fid` HAVING COUNT(f.`fid`) > 1) f INNER JOIN user u ON (u.uid=f.fid)-or- another one was
SELECT f.fid, u.name 'Woody and Andy\'s common friends' FROM
(SELECT a.fid FROM
(SELECT * FROM friends f
WHERE f.`uid`=1) a INNER JOIN
(SELECT * FROM friends f
WHERE f.`uid`=5) b ON (a.fid=b.fid)) f INNER JOIN user u ON (u.uid=f.fid)Both seem to work, but is there any elegant way of getting common friends in a much simpler SQL query? At this moment, I logically find first SQL query more intuitive since all it does is pickup friends who appear more than once when users are 1 and 5. The second SQL query seems plain brute force approach.
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Merging pre-sorted lists
A while ago, I came across an interesting problem. We have 3 different sorted queues (entries were sorted by time), out of which we had to pickup the smallest time, and send the first arrived entry out of those 3 queues in sequence.
Q1 Q2 Q3 2 3 1 5 4 6 7 6 9 8 10 11 As you can see, all queues (Q1, Q2, Q3) are already sorted, but on application side we have to pickup entries across all queues in sorted order and process them. So the entries should be processed in 1, 2, 3, 4, 5, … 11 sequence. Frankly this is merging of already sorted lists, and a person from computer science background should already know this. But I don’t come from such background, and the solution one of my friends gave was plain amazing.
The solution was pickup first entry from each queue, compare them, choose the smallest and process it first.
Q1 Q2 Q3 Smallest 2 3 1 1 Thus, here 1 is processed first. Now pickup next entry from queue where smallest was found (Q3 in this example), so now the next comparison becomes like this
Q1 Q2 Q3 Smallest 2 3 6 2 The smallest is 2, so this is processed and next entry from Q1 was picked-up
Q1 Q2 Q3 Smallest 5 3 6 3 And so on… giving us
Q1 Q2 Q3 Smallest 2 3 1 1 2 3 6 2 5 3 6 3 5 4 6 4 5 6 6 5 7 6 6 6 7 10 6 6 7 10 9 7 8 10 9 8 10 9 9 10 11 10 11 11 A simple, and elegant solution, isn’t it? Is there any other better alternative?
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Outlook export to Thunderbird
There is no straight (should I say “easy”) way to export Outlook mails to Thunderbird. Using Thunderbird’s import from Outlook did not work since quite a few emails came up as raw HTML, and I had to manually change Automatic encoding detection to OFF, Universal to see the contents each time.
A sure-shot (well… which took me 99% of the) way was Outlook –> Import into Outlook Express –> Import into Thunderbird. This worked, but with one sad issue – non-English attachment names are not as original. If you can live with that, then this is the surest way to go !Few references which helped-
Import .pst files – MozillaZine KB -
Extremely useful tips for Java
- 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.
- If no package is specified for class, it belongs to unnamed package – which cannot be imported.
- 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.
- 8 primitive types (byte, short, int, long, float, double, char, boolean), special type void, and base type for all objects – java.lang.Object.
- null is not a keyword, type. It is a value.
- 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” onString B= "a string";will point to same string object on heap. - Object gets garbage-collected, not it’s reference.
- Garbage collection is indeterminate. You cannot guarantee freeing of memory by forcing
System.gc() finalizemethod is invoked only once before being removed from memory. Always callsuper.finalize()if you override it.- 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.
- Return values from function are also passed by value, never by reference.
- Compound operators (+=, -=, *= etc) automatically cast. Compiler never throws any error on data mismatch.
- & (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
- char supports increment, decrement operators.
- The default isequal() implementation of Object tests for reference equality, which is same as ==.
- When using operators, Java automatically promotes values to int or higher. For values below int – byte, short – an explicit cast is required.
- extends comes first then implements
- Java tokenizes your source into separators (tab or space), keywords, operators, literals, identifiers (variable names).
- new zeroes Object’s fields (instance variables), hence explicit initialization can be skipped.
- 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.
- local variables must be initialized before using. Though method parameters are local variables too, since methods are called with parameters, they are initialized.
- arrays are fixed size data structures, where as collections are dynamically sized data structures.
- For multidimensional arrays, it is easier to imagine the first dimension as a single row containing the other dimensions.
- 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.
- There is always a default constructor – empty body – available for your class only if you do not declare any constructor.
- super, this must be the first line in constructor. this() or super() both cannot be placed.
- Parent class constructor super() is always called. For this reason, you need to have an empty constructor always in parent class.
- 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.
- Javabean properties are get-, set- methods provided over a field in Javabean style.
- 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)
- Overloading means providing different method signatures in same or inheriting class. Overriding means providing same return type, method signature in inheriting class.
- Covariant return types means overriding method returns a subclass of return type in parent class. (Java 5.0)
- Method hiding means overriding of static methods.
- Abstract method has no body. Interface methods are all abstract, while Abstract class can contain zero or more abstract methods.
- All abstract method of Interface are public, it’s fields are public, static and final. No static methods are allowed.
- 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.
- Enum constructors are invoked for each element.
- Anonymous inner class can have only one instance. Local inner class can have multiple instances.
- Static nested class is similar to any top-level class.
- Static fields in class always need default value; otherwise code does not compile.
- false is boolean, 0 is not false, it is int zero
- switch…case does not allow case null, since a constant (and final) expression is required for case
- You can put break in default for switch
- enum classes can have main method
- for(;;) is a valid for-loop. It never finishes, since it is an infinite loop.
- In enhanced for loop, the variable used for iteration must be declared only in for loop, not outside it.
- Java complains if you have unreachable while loop code e.g while(false) is not allowed. However, contrarily if(false) is allowed!
- Variables declared inside do…while loop are not available in while to test for condition!
- It is a good idea to add labels to your loops to enhance readability
- Assertion is put in places in your code where you think it should be always true
- Though not a good design, but assertions do allow modification on variables while asserting them e.g. assert ++i
- try…catch – catch can never have an exception which is a subclass of previous catch clause. It throws compile error.
- 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.
- try… must have either catch or finally atleast, otherwise compile gives error
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Colors to your life
Very often we are impressed with awe when we see a beautiful picture, photo, advert. The colors, their combination presents an alluring view just right for our eyes. If you notice more closer, you can seeing that more often the colors are complemented (red with white, green with blue…) to give a undistracted overall look. This is essentially because our eyes find this visually pleasant.
I have a tool which can offer such combinations, and you should design your color combinations using the suggested patterns
http://9i9.me/colors/index.html/ – For visually stunning color combinations
Keep working!
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Japanese women hate their husbands
See top searches coming from Google for おっと (husband) in Japanese
Japanese women hate husbands Almost all top suggestions refer to “husband should die”. I wonder what results are returned?
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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 !
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” !