In Java random integers in range can be produced in many ways. In this post we show how to generate random numbers using Java 8 features!
Random integers using for loop
List<Integer> forLoopRange(int limit, int from, int to) {
Random random = new Random();
int bound = to-from;
List<Integer> numbers = new ArrayList<>(limit);
for (int i = 1; i <= limit; i++) {
numbers.add(random.nextInt(bound)+from);
}
return numbers;
}
When can call the above code with sample parameters – forLoopRange(limit, 20, 30):
[25, 25, 21, 26, 21, 20, 28, 28, 25, 29]
Random integers from Random.ints
The shortest and most convenient way to generate random range of integers is to use new in Java 8 method Random.ints() that returns IntStream of random ints:
List<Integer> randomInts(int limit, int from, int to) {
Random rand = new Random();
return rand.ints(limit, from, to).boxed().collect(toList());
}
Let’s execute it with sample parameters – randomInts(limit, 10, 20):
[17, 17, 18, 15, 19, 14, 18, 17, 19, 12]
Random numbers with IntStream.generate()
If you would like to provide your source of random numbers you can do so and generate random integers in range with IntStream.generate() like here:
List<Integer> streamRandomRange(int limit, int from, int to) {
// use your source of entrophy here:
Random rand = new Random();
int bound = to - from;
return IntStream.generate(() -> rand.nextInt(bound)+from)
.limit(limit)
.boxed()
.collect(toList());
}
Sample execution of streamRandomRange(limit, 80, 90):
[82, 80, 85, 88, 89, 87, 85, 88, 82, 83]
References:
- How to generate range of numbers
- Check out Java Util Tutorial for more Java 8 cool features!
