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Android: regex for edit text to have only 2 values possible in decimal

In my filter used into EditText, I want to be sure the user can only set .5 or .0 for decimal values.
Valid values examples:
34.5
34.0
34
Invalid values examples:
34.2
34.8
34.6
I tried this one, but it doesn't work properly: [0-9]*[.]?[0|5]
Thank you very much guys!

You're probably looking for [0-9]*(\.([50][0]*)*)*.
[0-9]*: Any character from 0 to 9, zero or more times [so that just a "." (= 0.0) input is valid]
\.: You need to escape the '.' character, since it usually would mean "any character", and you especifically need the dot there.
[50][0]*: First, either five or zero (once). Second, the 0 character, zero or more times (since 35.50 = 35.5). This also avoids inputs like 35.59 from being valid, since 9 != 0.
([50][0]*)*: This occurrence zero or more times, so that 35., for instance, becomes a valid input (since 35. = 35.0).
(\.([50][0]*)*)*: As for this grouping, it's in order to check for the five or the zero only if there is a decimal dot. It's grouping the dot character and the 5/0 logic together with a star (zero or more times) at the end, so if it doesn't occur, it still matches.
Let me know if this was what you were looking for.

To verify the whole numbers in the examples, you can make the last part optional and use anchors.
^[0-9]+(?:[.][05])?$
^ Start of string
[0-9]+ Match 1+ digits 0-9
(?:[.][05])? Optionally match . and a digit 0 or 5
$ End of string
See a regex demo.
If you want to be able to only type a pattern like that and also accept empty strings or 34. you can repeat the digit 0 or more times, optionally match . and optionally match either 0 or 5.
^[0-9]*[.]?[05]?$
See another regex demo

Use enum with number

I know there are many alternatives to reach what I wish, but I wont this solution because it is the most comfortable to me. I wish to use enum that starts with number, like so.
public enum Quality {
1080p,
720p,
BlueRay //this one OK
}
And then use it like so when converting to string:
Quality.1080p.name();
Why it is not possible?

Because the Java language doesn't allow variable names to start with a number- just a letter or underscore. Any character after the first may be a number. The main reason for this is to make parsing easier, and prevent situations where the parser can't tell if a symbol is a number or a variable name.
For example, if numbers were valid at the start of a variable I could do the following:
String 1 = "string";
System.out.println(1);
Does this print 1 or "string"? They avoid the problem by not allowing it. Many (most?) languages have that restriction.

getting value 9.777123455E9 instead of 9777123455 from excel sheet

I am working on a project in which i am getting value from excel sheet(in assets android) and reflecting data in list view.
problem is:: phone no is not in proper format.
9.777123455E9 instead of 9777123455

When it's a phone number, you should always store the cell data as text, even if it consists only of digits, since a phone number is no mathematical number and when doing operations on it, you want to treat it as a string of characters (i.e. text).
If you input a phone number that looks to Excel like a mathematical number, it will interpret it as a number and in consequence will do things to it that make sense for numbers, but not necessarily for phone numbers, such as displaying it in scientific format.
To force Excel to treat your number as text, precede it with a single quote (apostrophe) when entering it. That is, enter into the cell:
'9777123455
It will be displayed without the single quote, just as you expect a phone number to be displayed and can be processed as text.

double d=9.777123455E9;
NumberFormat formatter = new DecimalFormat("#");
System.out.println(d);
System.out.println(formatter.format(d));
output
9.777123455E9
9777123455

E9 simply means multiply by 10^9
Update:
As #blubberdiblub mentioned, for phone numbers, it makes sense to change it to text. But for other cases, If you need to do mathematical operations leaving it in the scientific format works. You can right click on the column name and select formatting option to set the type of data the column will handle (number , text etc). If you want don't want to change the phone number to text and still see the number, simply increase the width of the column. The number will be shown full (without the "E").

Scan string for characters and return bounded text

I am writing a dictionary-type app. I have a list of hash-mapped terms and definitions. The basic premise is that there is a list of words that you tap on to see the definitions.
I have this functionality up and running - I am now trying to put dynamic links between the definitions.
Example: say the user taps on an item in the list, "dog". The definition might pop up, saying "A small furry [animal], commonly kept as a pet. See also [cat].". The intention is that the user can click on the word [animal] or [cat] and go to the appropriate definition. I've already gone to the trouble of making sure that any links in definitions are bounded by square brackets, so it's just a case of scanning the pop-up string for text [surrounded by brackets] and providing a link to that definition.
Note that definitions can contain multiple links, whilst some don't contain any links.
I have access to the string before it is displayed, so I guess the best way to do this is to do the scanning and ready the links before the dialog box is displayed.
The question is, how would I go about scanning for text surrounded by square brackets, and returning the text contained within those brackets?
Ideally the actual dialog box that is displayed would be devoid of the square brackets, and I need to also figure out a way of putting hyperlinks into a dialog box's text, but I'll cross that bridge when I come to it.
I'm new to Java - I've come from MATLAB and am just about staying afloat, but this is a less common task than I've had to deal with so far!

You could probably do this with a regular expression; something like this:
([^[]*)(\[[^]]+\])
which describes two "match groups"; the first of which means any string of zero or more characters that aren't "[" and the second of which means any string starting with "[", containing one or more characters that aren't "]", and ending with "]".
Then you could scan through your input for matches to this pattern. The first match group is passed through unchanged, and the second match group gets converted to a link. When the pattern stops matching your input, take whatever's left over and transmit that unchanged as well.
You'll have to experiment a little; regular expressions typically take some debugging. If your link text can only contain alphanumerics and spaces, your pattern would look more like this:
([^[]*)(\[[\s\w]+\])
Also, you may find that regular expression matching under Android is too slow to be practical, in which case you'll have to use wasyl's suggestion.

Quite simple, I think... As the text is in brackets, you need to scan every letter. So the basic recipe would be :
in a while loop scan every character (let's say, while i < len(text))
If scanned character is [:
i++;
Add letter at index i to some temporary variable
while (character # i) != ']' append it to the temporary variable
store this temporary variable in a list of results.
Some tips:
If you use solution above, use StringBuilder to append text (as regular string is immutable)
You might also want (and it's better, I think) to store starting and ending positions of all square brackets first, and then use string.substring() on each pair to get the text inside. This way you'd first iterate definition to find brackets (maybe catch unmatched ones, for early error handling), then iterate pairs of indices...
As for links, maybe this will be of use: How can I get clickable hyperlinks in AlertDialog from a string resource?

Doing order by using the Jaro-Winkler distance algorithm?

I am wondering how would I be able to run a SQLite order by in this manner
select * from contacts order by jarowinkler(contacts.name,'john smith');
I know Android has a bottleneck with user defined functions, do I have an alternative?

Step #1: Do the query minus the ORDER BY portion
Step #2: Create a CursorWrapper that wraps your Cursor, calculates the Jaro-Winkler distance for each position, sorts the positions, then uses the sorted positions when overriding all methods that require a position (e.g., moveToPosition(), moveToNext()).

Pre calculate string lengths and add them into separate column. Then sort entired table by that that length. Add indexes (if you can). Then add extra filters for example you don't want to compare "Srivastava Brahmaputra" to "John Smith". The length are out of wack by way too much so exclude these kind of comparison by length as a percentage of the total length. So if your word is 10 characters compare it only to words with 10+-2 or 10+-3 characters.
This way you will significantly reduce the number of times this algorithm needs to run.
Typically in the vocalbulary of 100 000 entries such filters reduce the number of comparisons to about 300. Unless you are doing a full blown record linkage and then I would wonder why use Android for that. You would still need to apply probabilistic methods for that and calculate scores and this is not a job for Android (at least not for now).
Also in MS SQL Server Jaro Winkler string distance wrapped into CLR function perform much better, since SQL Server doesn't supprt arays natively and much of the processing is around arrays. So implementation in T-SQL add too much overhead, but SQL-CLR works extremely fast.