For loop - like Python range function

Question

I was wondering if in Java there is a function like the python range function.

range(4)

and it would return

[0,1,2,3]
         


        

Answer 1

Without an external library, you can do the following. It will consume significantly less memory for big ranges than the current accepted answer, as there is no array created.

Have a class like this:

class Range implements Iterable {

    private int limit;

    public Range(int limit) {
        this.limit = limit;
    }

    @Override
    public Iterator iterator() {
        final int max = limit;
        return new Iterator() {

            private int current = 0;

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

            @Override
            public Integer next() {
                if (hasNext()) {
                    return current++;   
                } else {
                    throw new NoSuchElementException("Range reached the end");
                }
            }

            @Override
            public void remove() {
                throw new UnsupportedOperationException("Can't remove values from a Range");
            }
        };
    }
}

and you can simply use it like this:

    for (int i : new Range(5)) {
        System.out.println(i);
    }

you can even reuse it:

    Range range5 = new Range(5);

    for (int i : range5) {
        System.out.println(i);
    }
    for (int i : range5) {
        System.out.println(i);
    }

---

As Henry Keiter pointed out in the comment below, we could add following method to the Range class (or anywhere else):

public static Range range(int max) {
    return new Range(max);
}

and then, in the other classes we can

import static package.name.Range.range;

and simply call

for (int i : range(5)) {
    System.out.println(i);
}