Differentiate between function in Java and C

Of course  you cannot conclude that

return_type function_name()

is always C function

there maybe any number of Java Methods
like that, say,

float my_function()

You need to have the context.

One very imporatnt difference that in Java all methods
should be within a class, whereas in C++ there may be
functions and methods not within any class

I think in C++ there is a function ToCharArray():
http://msdn.microsoft.com/en-us/library/system.string.tochararray%28v=vs.71%29.aspx

But still toCharArra() - starting with lower case looks more like Java to me.
Of course you cannot rely on such things - no one prevents someone to
write in C function with such name

Thanks for the detailed explanations.

Can you tell me if "len = s.Length" is C or Java?

I think one simple way is to look at the top of the program - in C you'll usually
see a bunch of "include"'s, in Java - a bunch of "import"'s

s is an array.

Is "s.Length" in Java? (L is in caps)

I have access only to the function code...

Do all Java functions need the qualifier "public" / "private", etc?

No, nota ll of them need it - they have no access qualifie - that is called
"default" access - just you may write

float sqrt1(float x){...}

it is return type which is mandatory in Java - even if returns nothing it should have "void" in frtont; I guess in C - if it returns nothing "void" is just good practice but not an error

But one exception is that constructor in the class has no return type - but its name should be identical to the name of the class - so if compiler ebcounetrs declaration of method which has no return type and does not match exactly the class name where it finds this method - then Java compiler will report an error