Populating a List with a contiguous range of integers

Question

I\'d like to have a list which contains the integers in the range 1 to 500. Is there some way to create this list using Guava (or just plain Java) without having to loop th

Answer 1

The new, Java 8, way:

List<Integer> range = IntStream.range(0, 500).boxed().collect(Collectors.toList());

Answer 2

You can also use Apache Commons IntRange utility

E.g.

    private List<Integer> getAllIntegerRange(Integer firstValue, Integer secondValue) {
    List<Integer> values = new ArrayList<>();
    IntRange rang = new IntRange(firstValue, secondValue);
    int[] ranges = rang.toArray();
    for (int i : ranges) {
        values.add(i);
    }
    return values;
}

Answer 3

Using Guava, you can resort to a Range: http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/collect/Range.html

Of course, there will still be loops in your code, but they just might be hidden from the code for simplicity sake.

For instance:

Range<Integer> yourValues = Range.closed(1, 500);

Check http://code.google.com/p/guava-libraries/wiki/RangesExplained for some more examples.

Keep in mind that if you do need to eventually iterate over the Range, you cannot do so directly, only through using DiscreteDomains.integers().

Answer 4

Btw. if it is only to be used in some sort of iteration, you could simply create a basic class which implements the Iterable interface, to skip the insertion altogether.

Something like this:

import java.util.Iterator;

public class IntegerRange implements Iterable<Integer> {
    private int start, end;

    public IntegerRange(int start, int end) {
        if (start <= end) {
            this.start = start;
            this.end = end;
        } else {
            this.start = end;
            this.end = start;
        }
    }

    @Override
    public Iterator<Integer> iterator() {
        return new IntegerRangeIterator();
    }

    private class IntegerRangeIterator implements Iterator<Integer> {
        private int current = start;

        @Override
        public boolean hasNext() {
            return current <= end;
        }

        @Override
        public Integer next() {
            return current++;
        }
    }
}

Which could be used in some way like this:

Iterable<Integer> range = new IntegerRange(1, 500);

for (int i : range) {
    // ... do something with the integer
}