optaplanner-core/src/main/java/org/optaplanner/core/impl/solver/random/RandomUtils.java
public static long nextLong(Random random, long n) {
        // This code is based on java.util.Random#nextInt(int)'s javadoc.
        if (n <= 0L) {
            throw new IllegalArgumentException("n must be positive");
        }
        if (n < Integer.MAX_VALUE) {
            return (long) random.nextInt((int) n);
        }

        long bits;
        long val;
        do {
            bits = (random.nextLong() << 1) >>> 1;
            val = bits % n;
        } while (bits - val + (n - 1L) < 0L);
        return val;
    }
public static long nextLong(Random random, long n) {
        // This code is based on java.util.Random#nextInt(int)'s javadoc.
        if (n <= 0L) {
            throw new IllegalArgumentException("n must be positive");
        }
        if (n < Integer.MAX_VALUE) {
            return (long) random.nextInt((int) n);
        }

        long bits;
        long val;
        do {
            bits = (random.nextLong() << 1) >>> 1;
            val = bits % n;
        } while (bits - val + (n - 1L) < 0L);
        return val;
    }
Mimics {@link Random#nextInt(int)} for longs.
@param random never null
@param n {@code > 0L}
@return like {@link Random#nextInt(int)} but for a long
@see Random#nextInt(int)