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..

the codes are stored in an enum where per function getCodes an ArrayList<String> is returned — Inuendo
– Inuendo, Commented Aug 11, 2016 at 10:22

fabian · Accepted Answer · 2017-09-21 14:44:35Z

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 (%).

edited Sep 21, 2017 at 14:44

answered Aug 11, 2016 at 10:01

fabian

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Comments

Ray O'Kalahjan · Accepted Answer · 2016-08-11 10:04:28Z

0

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;
    }
}

answered Aug 11, 2016 at 10:04

Ray O'Kalahjan

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Bohemian · Accepted Answer · 2016-08-11 10:12:34Z

0

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];

edited Aug 11, 2016 at 10:12

answered Aug 11, 2016 at 10:06

Bohemian♦

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Comments

whyn0t · Accepted Answer · 2016-08-11 10:21:39Z

0

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));

}

answered Aug 11, 2016 at 10:21

whyn0t

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