CODEWITHSUNDEEP
java
Code Junkie
Code Junkie

Reputation: 7788

Create range of years from start to end.

I'm looking for the simplest way to create range of years that I can put into a list starting with a from year and ending with an end year.

Example 

String fromYear = "2010"
String toYear = "2014"

expecting to create a list of years ["2010","2011","2012","2013","2014"]

No I know I need to convert the string to an Integer

Integer from = fromYear != null ? Integer.parseInt(fromYear) : null;
Integer to = toYear != null ? Integer.parseInt(toYear) : null;

From there I'm lost as for the most efficient way to complete this.

Upvotes: 5

Views: 3365

Answers (4)

sparc_spread
sparc_spread

Reputation: 10843

Here's what it's like with the new Java 8 streams API. I am going to assume that there is no use case where either year could be null, and will thus throw an error if one of them is:

String fromYear = "2010" ;
String toYear = "2014" ;

List<Integer> years =
        IntStream.rangeClosed
                (Integer.parseInt(Objects.requireNonNull(fromYear)),
                 Integer.parseInt(Objects.requireNonNull(toYear)))
        .boxed()
        .collect(Collectors.toList());

Steps correspond roughly to: ensure fromYear and toYear are both non-null, else throw an exception; convert fromYear and toYear to integers; create a stream of int values beginning with fromYear and ending with toYear; convert them into Integer instances (that's boxed()); and package them as a list.

Upvotes: 5

enrico.bacis
enrico.bacis

Reputation: 31514

You should not create such a specific function that takes strings, it's normally better to have a range function that takes ints and convert the strings using Integer.parseInt as you already said in the question.

Then you can define your own function:

public static List<Integer> range(int from, int to) {
    List<Integer> list = new ArrayList<Integer>();
    for (int i = from; i <= to; ++i)
        list.add(i);
    return list;
}

Otherwise if you are using Java 8 take a look at IntStream.rangeClosed. You could also use Guava's Range, they are nice because using iterators, they don't have to physically instantiate the list.

Upvotes: 3

SparkOn
SparkOn

Reputation: 8956

Treat Date as a Date

String fromYear = "2010";
String toYear = "2014";
SimpleDateFormat df = new SimpleDateFormat("yyyy", Locale.ENGLISH);
List<String> listOfDates = new ArrayList();
Calendar startCal = Calendar.getInstance(Locale.ENGLISH);
startCal.setTime(df.parse(fromYear));
Calendar endCal = Calendar.getInstance(Locale.ENGLISH);
endCal.setTime(df.parse(toYear));
while (startCal.getTimeInMillis() <= endCal.getTimeInMillis()){
    java.util.Date date = startCal.getTime();
    listOfDates.add(new SimpleDateFormat("yyyy", Locale.ENGLISH).format(date).trim());
    startCal.add(Calendar.YEAR, 1);
}
System.out.println(listOfDates);

Upvotes: 1

arkon
arkon

Reputation: 2296

Takes String arguments, converts and returns Integer list:

public static List<Integer> range(String startYear, String endYear) {
    int cur = Integer.parseInt(startYear);
    int stop = Integer.parseInt(endYear);
    List<Integer> list = new ArrayList<Integer>();
    while (cur <= stop) {
        list.add(cur++);
    }
    return list;
}

Or if you need to return String list:

public static List<String> range(String startYear, String endYear) {
    int cur = Integer.parseInt(startYear);
    int stop = Integer.parseInt(endYear);
    List<String> list = new ArrayList<String>();
    while (cur <= stop) {
        list.add(String.valueOf(cur++));
    }
    return list;
}

Upvotes: 4

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