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]

This was an easy way to make for enhanced loops. It would be great to do this in Java because it would make for loops a lot easier. Is this possible?

Answer 1

Java 8 (2014) has added IntStream (similar to apache commons IntRange), so you don't need external lib now.

import java.util.stream.IntStream;   IntStream.range(0, 3).forEachOrdered(n -> {     System.out.println(n); }); 

forEach can be used in place of forEachOrdered too if order is not important.

IntStream.range(0, 3).parallel() can be used for loops to run in parallel

Answer 2

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<Integer> {      private int limit;      public Range(int limit) {         this.limit = limit;     }      @Override     public Iterator<Integer> iterator() {         final int max = limit;         return new Iterator<Integer>() {              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); } 

Answer 3

Um... for (int i = 0; i < k; i++)? You don't have to write enhanced for loops all day, you know, although they are cool...

And just for the sake of argument:

for (int i : range(k)) char count: 22

for (int i = 0; i < k; i++) char count: 27

Discounting the implementation of range, it is pseudo even.

Answer 4

Use Apache Commons Lang:

new IntRange(0, 3).toArray();

I wouldn't normally advocate introducing external libraries for something so simple, but Apache Commons are so widely used that you probably already have it in your project!

Edit: I know its not necessarily as simple or fast as a for loop, but its a nice bit of syntactic sugar that makes the intent clear.

Edit: See @zengr's answer using IntStream in Java 8 .