Java Merge two Lists of different size to a HashMap

Question

I need some hints on this: I have lets say a list or a sequence of years with

int startYear = 2010;
int endYear = 2050;

and i have an enum with letters and digits as year codes.

I need this for Barcode generation where i have a timestamp that need to be coded into 3 digits/letters, so i need to map year month and day to a code position.

What i need to do is to map the year sequence to the codes list into a HashMap of keys (the year numbers) and values (the year codes),

but obviously the codes list is not as long as the year sequence so i need to check when the last index is reached and if yes i need to reloop through the codes list until the end of the year sequence is reached.

what i need to achieve is this:

year    code
2012     C
2013     D
.
.
2030     Y
2031     1
.
.
2039     9
2040     A

and so on...

unfortunately i could not figure out a way how to do this, couse I'm pretty new to java so I'd appreciate if someone can give me some advice..

Answer 1

Simply use the % operator to calculate the code index

List years = ...
List codes = ...
for (int i = 0, yearsSize = years.size(), codesSize = codes.size(); i < yearsSize; i++) {
     map.put(years.get(i), codes.get(i % codesSize));
}

See Remainder Operator (%) .

Answer 2

How about something like this?:
Assuming:

public enum Code {
    A, B, C, ... Z, 1, ... 9;
}
List<Integer> years;
HashMap<Integer,Code> map;

Just add an index for the code which will initialize if too big:

int i = 0;
for(Integer year : years) {
    map.push(year, Code.values()[i];
    i++;
    if(i >= Code.values().length) {
        i = 0;
    }
}

Answer 3

Before encoding the year, modulous the year so the %year% loops:

int yearToEncode = 2012 + ((year - 2012) % MyEnum.values().length);

Assuming that 2012 is "year zero".

Then you can use:

MyEnum encodedYear = MyEnum.values()[yearToEncode - 2012];

But your code would be a whole lot simpler if year zero was arbitrary:

MyEnum[] codes = MyEnum.values();
MyEnum encodedYear = codes[year % codes.length];

Answer 4

try this you can even change the start year and end year

int yStart = 2010;
int yEnd = 2050;
String s  = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"; 
int pos = 0;
for(int i = yStart; i < yEnd; i++){
    pos = (i - yStart)%s.length();
    map.put(i, s.substring(pos, pos+1));// put in map
    System.out.println(i + "  " + s.substring(pos, pos+1));

}