Java Generate List From 1 to N

September 21, 2024

There are several ways to generate a list from 1 to n in Java.

Using a Loop

import java.util.ArrayList;
import java.util.List;

public class GenerateListFrom1ToNUsingLoopMain {
    public static void main(String[] args) {
        int n = 10;

        List<Integer> list = new ArrayList<>(n);
        for (int i = 1; i <= n; i++) {
            list.add(i);
        }

        System.out.println(list); // [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
    }
}

Also, loop can be re-written as 0…N-1:

import java.util.ArrayList;
import java.util.List;

public class GenerateListFrom1ToNUsingLoopMain {
    public static void main(String[] args) {
        int n = 10;

        List<Integer> list = new ArrayList<>(n);
        for (int i = 0; i < n; i++) {
            list.add(i + 1);
        }

        System.out.println(list); // [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
    }
}

Using IntStream

This example uses the Java Stream API for a more functional and concise approach.

import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class GenerateListFrom1ToNUsingIntStreamMain {
    public static void main(String[] args) {
        int n = 10;

        List<Integer> list = IntStream.rangeClosed(1, n)
                .boxed()
                .collect(Collectors.toList());

        System.out.println(list); // [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
    }
}

Since Java 16, there is Stream::toList method and last example can be simplified:

import java.util.stream.IntStream;

public class GenerateListFrom1ToNUsingIntStreamJava16Main {
    public static void main(String[] args) {
        int n = 10;

        var list = IntStream.rangeClosed(1, n)
                .boxed()
                .toList();

        System.out.println(list); // [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
    }
}