Find a "date" from a table - calendar

Question

I want to create a "Table" which is like a calendar with all months and days from 1-31. But what I want to do is: If the user picks a months and a day it has to give you a number (not random) For example
Days | Ene | Feb | Mar
----------------------
1 | A1 | A4 | A7
---------------------
2 | A2 | A5 | A8
---------------------
3 | A3 | A6 | A9
---------------------
If the user write or pick Ene 1, he will get A1 or Feb 2, will get A5 (and so on). That's the questions, how can I build it? PHP? Javascript? Java? Using SQL/DataBases?

Answer 1

tl;dr
map.get( Month.FEBRUARY ).get( 2 - 1 )
A5
Java
Month enum
First, you should know that Java has pre-defined a set of 12 objects for the months, in the Month enum. By the way, the enum facility in Java is much more powerful and flexible than is usual in most languages; you may want to learn more.
By the way, you can ask the Month class to automatically localize the name of the month via the getDisplayName method.
List
You numbers happen to be 1, 2, 3, so we can use those to access a List.
Unfortunately, access into a List is only provided as an index, meaning 0-based counting (an unfortunate hangover from the early days of programming). So we must subtract one from the day-of-month. For example, for the 1st, use 0, for the 2nd, use 1.
Map
We can map each month to its list of values using a Map.
Collection literals
Java 9 brings handy new Map.ofEntries and List.of methods for concisely generating unmodifiable collections.
Map< Month, List< String > > map =
Map.ofEntries(
entry( Month.JANUARY , List.of( "A1" , "A2" , "A3" ) ) , // This syntax requires at top: import static java.util.Map.entry ;
entry( Month.FEBRUARY , List.of( "A4" , "A5" , "A6" ) ) ,
entry( Month.MARCH , List.of( "A7" , "A8" , "A9" ) )
)
;
Accessing Map and List
Try it out. Simulate the user’s input of a month and day.
Month m = Month.FEBRUARY;
int dayOfMonth = 2;
Or get the month by number, 1-12 for January-December.
Month m= Month.of( 2 );
Access our Map to get that month’s List. Passing a Month object gets us back the List object we had put into the map.
List< String > list = map.get( m );
Access that List to get our desired String, such as A5.
String result = list.get( dayOfMonth - 1 ); // Subtract one for zero-based index.
Or, combine those two lines into one, accessing both the Map and the List.
String result = map.get( m ).get( dayOfMonth - 1 ); // One-liner, alternative.
A5
Let’s see all that code together.
Map< Month, List< String > > map = Map.ofEntries(
entry( Month.JANUARY , List.of( "A1" , "A2" , "A3" ) ) , // This syntax requires at top: import static java.util.Map.entry ;
entry( Month.FEBRUARY , List.of( "A4" , "A5" , "A6" ) ) ,
entry( Month.MARCH , List.of( "A7" , "A8" , "A9" ) )
);
Month m = Month.FEBRUARY; // Or, Month.of( 2 )
int dayOfMonth = 2;
List< String > list = map.get( m ); // Passing a `Month` object gets us back the `List` object we had put into the map.
String result = list.get( dayOfMonth - 1 ); // Subtract one for zero-based index counting to access `List`.
String result2 = map.get( m ).get( dayOfMonth - 1 ); // One-liner, alternative.