Post S2 I9100G ICS Upgrade: Only Samsung Logo Left?

I decided to upgrade my Samsung S2 I9100G from Gingerbread to ICS; used the software update on the phone to perform the upgrade; now my phone would boot and show the Samsung logo for eternity!

The only way to get the phone back to work is to revert to Gingerbread! This has to be done manually by downloading the firmware and installing it.

Thanks to this link , it provides a detailed explanation for doing the same.

Appreciate Samsung for such robust update release which only shows their logo after its applied!

Of course, I can visit the Samsung service center in Bangalore which is worse than their upgrade package!

loadClass - JDK 1.6.0_18 vs JDK 1.6.0_27

Recently while implementing a custom class loader, I hit upon a issue related to loadClass method of the Classloader.  The custom classloader code of interest is below.

	protected synchronized Class<?> loadClass(String name, boolean resolve)
	throws ClassNotFoundException
	{
	if( name.contains("xxxx") ){
	return null;
	}
	return super.loadClass(name,resolve);
	}

view raw custom_cl.java hosted with ❤ by GitHub

This classloader worked on JDK 6 Update 27 (dev env) but failed to work on JDK 6 Update 17 (test env).


Its a rare skill to write code in Java that  fails between minor revisions!! :-)

The class loader code was written looking at the Java source code for Classloader. This was the cause of the issue - the custom loader implementation did not adhere to the documented contract for the loadClass method.

The documentation of the loadClass method clearly states

Throws:

ClassNotFoundException - If the class could not be found

While the custom class loader method returns null if the class is not found! So why did it work in latest update of Java?  Following are the Classloader code snippets from the two JDK 6 updates that I have mentioned.

Jdk 1.6 Update 18

	protected synchronized Class<?> loadClass(String name, boolean resolve)
	throws ClassNotFoundException
	{
	// First, check if the class has already been loaded
	Class c = findLoadedClass(name);
	if (c == null) {
	try {
	if (parent != null) {
	c = parent.loadClass(name, false);
	} else {
	c = findBootstrapClass0(name);
	}
	} catch (ClassNotFoundException e) {
	// If still not found, then invoke findClass in order
	// to find the class.
	c = findClass(name);
	}
	}
	if (resolve) {
	resolveClass(c);
	}
	return c;
	}

view raw Jdk1.6.0_18.java hosted with ❤ by GitHub

Jdk 1.6 Update 27

	protected synchronized Class<?> loadClass(String name, boolean resolve)
	throws ClassNotFoundException
	{
	// First, check if the class has already been loaded
	Class c = findLoadedClass(name);
	if (c == null) {
	try {
	if (parent != null) {
	c = parent.loadClass(name, false);
	} else {
	c = findBootstrapClassOrNull(name);
	}
	} catch (ClassNotFoundException e) {
	// ClassNotFoundException thrown if class not found
	// from the non-null parent class loader
	}
	if (c == null) {
	// If still not found, then invoke findClass in order
	// to find the class.
	c = findClass(name);
	}
	}
	if (resolve) {
	resolveClass(c);
	}
	return c;
	}

view raw Jdk1.6.0_27.java hosted with ❤ by GitHub

The if check c==null in the Update 27 made the loadClass method work even though it did not adhere to the documented contract.

The bottom line is to code against documented contract and not look at the implementation to write code!

Analytical Reasoning With Prolog

Last year, I solved the following analytical reasoning problem by hand. Post learning Prolog, I think this is a good problem to solve using a computer! I had a interesting experience doing so.

Problem:

Facts:

1: There are 5 villas in 5 different colors 

2: In each villa lives a person with a different nationality. 

3: These 5 owners drink a certain beverage, smoke a certain brand of cigar and keep a certain pet. 

4: No owner has the same pet, smoke the same brand of cigar or drink the same drink.

Hints:

1: The British lives in a red villa. 

2: The Swede keeps dogs as pets 

3: The Dane drinks tea 

4: The green villa is on the left of the white villa (it also means they are next door to each other) 

5: The green villa owner drinks coffee 

6: The person who smokes Pall Mall rears birds 

7: The owner of the yellow villa smokes Dunhill 

8: The man living in the villa right in the center drinks milk 

9: The Norwegian lives in the first villa 

10: The man who smokes Blend lives next to the one who keeps cats 

11: The man who keeps horses lives next to the man who smokes Dunhill 

12: The owner who smokes Blue Master drinks beer 

13: The German smokes Prince 

14: The Norwegian lives next to the blue villa 

15: The man who smokes Blend has a neighbor who drinks water.

The question is: who keeps the fish?

Prolog Solution:

The following is what i could come up with after serval iterations through code.

	#!/opt/local/bin/gprolog --consult-file
	segment([H1,H2],[H1,H2]):-!.
	segment([H1,H2],[H1,H2|_]):-!.
	segment([H1,H2],[_,H4|T2]) :- segment([H1,H2],[H4|T2]).
	adjacent([H1,H2],L1,L2) :- segment([H1,H2],L1),!;segment([H2,H1],L2),!.
	valid_set([],_,_).
	valid_set([H|T],Y,AL):- member(H,Y), \+(member(H,AL)), valid_set(T,Y,[H|AL]).
	valid_values(L,Y):- valid_set(L,Y,[]).
	villas :-
	Solution =[
	(1,N1,C1,D1,S1,P1),
	(2,N2,C2,D2,S2,P2),
	(3,N3,C3,D3,S3,P3),
	(4,N4,C4,D4,S4,P4),
	(5,N5,C5,D5,S5,P5)
	],
	% 9: Norwegian lives in first villa.
	N1=norwegian,
	% 8: Man living in the center villa drinks milk.
	D3=milk,
	valid_values([C1,C2,C3,C4,C5],[green,white,yellow,blue,red]),
	% 4: Green villa is left of white villa.
	segment([green,white],[C1,C2,C3,C4,C5]),
	valid_values([N2,N3,N4,N5],[dane,german,british,swede]),
	% 1: British lives in a red villa.
	segment([british,red],[N1,C1,N2,C2,N3,C3,N4,C4,N5,C5]),
	% 14: Norwegian lives next to blue villa.
	segment([norwegian,blue],[N1,C2,N2,C3,N3,C4,N4,C5]),
	valid_values([D1,D2,D4,D5],[coffee,beer,water,tea]),
	% 5: Green villa owner drinks coffee.
	segment([green,coffee],[C1,D1,C2,D2,C3,D3,C4,D4,C5,D5]),
	% 3: Dane drinks tea.
	segment([dane,tea],[N1,D1,N2,D2,N3,D3,N4,D4,N5,D5]),
	valid_values([S1,S2,S3,S4,S5],[pallmall,dunhill,blend,bluemaster,prince]),
	% 13: German Smokes Prince.
	segment([german,prince],[N1,S1,N2,S2,N3,S3,N4,S4,N5,S5]),
	% 12: Owner who smokes Bluemaster drinks beer.
	segment([bluemaster,beer],[S1,D1,S2,D2,S3,D3,S4,D4,S5,D5]),
	valid_values([P1,P2,P3,P4,P5],[fish,cat,birds,horse,dog]),
	% 2: Swede keeps dogs as pets.
	segment([swede,dog],[N1,P1,N2,P2,N3,P3,N4,P4,N5,P5]),
	% 6: Person who smokes pallmall rears birds.
	segment([pallmall,birds],[S1,P1,S2,P2,S3,P3,S4,P4,S5,P5]),
	% 7: Owner of yellow vill smokes Dunhill.
	segment([yellow,dunhill],[C1,S1,C2,S2,C3,S3,C4,S4,C5,S5]),
	% 15: Man who smokes Blend has a neighbor who dinks water.
	adjacent([blend,water],[S1,D2,S2,D3,S3,D4,S4,D5],[D1,S2,D2,S3,D3,S4,D4,S5]),
	% 10: Man who smokes Blend lives next to the man who keeps cats.
	adjacent([blend,cat],[S1,P2,S2,P3,S3,P4,S4,P5],[P1,S2,P2,S3,P3,S4,P4,S5]),
	% 11: Man who keeps horses lives next to man who smokes Dunhill.
	adjacent([dunhill,horse],[S1,P2,S2,P3,S3,P4,S4,P5],[P1,S2,P2,S3,P3,S4,P4,S5]),
	printSol(Solution).
	printSol([]).
	printSol([H|T]) :- write(H),nl,printSol(T).

view raw 5villas.prolog hosted with ❤ by GitHub

Answer to Puzzle:

Following is the output of the prolog program.

1,norwegian,yellow,water,dunhill,cat

2,dane,blue,tea,blend,horse

3,british,red,milk,pallmall,birds

4,german,green,coffee,prince,fish

5,swede,white,beer,bluemaster,dog

Hence the answer is German keeps the fish.