Why a Java Program Using Random with Fixed Seeds Always Prints "Hello world"

This article examines a Java program that appears to generate random strings but consistently outputs the phrase "Hello world".

import java.util.*; public class HelloWorld{ public static String randomString(int i){ Random ran = new Random(i); StringBuilder sb = new StringBuilder(); for (int n = 0; ; n++){ int k = ran.nextInt(27); if (k == 0) break; sb.append((char)('`' + k)); } return sb.toString(); } public static void main(String[] args){ System.out.println(randomString(-229985452)+" "+randomString(-147909649)); } }

The key point is that each Random object is created with a specific integer seed (‑229985452 and ‑147909649). In Java, a Random instance seeded with the same value will generate the same sequence of numbers on every run, because the algorithm is deterministic.

For the first seed the generated numbers are 8 5 12 12 15 0 ; for the second seed they are 23 15 18 12 4 0 . Each number k is added to the ASCII code of the back‑tick character ( '`' , value 96) and cast to a character, producing the letters h‑e‑l‑l‑o‑w‑o‑r‑l‑d, i.e., "Hello world".

Thus the program always prints the same result, illustrating the concept of pseudo‑random numbers: when the seed is fixed, the output is predictable. The article also references the original Stack Overflow discussion and notes that this behavior is a classic example of deterministic pseudo‑random generation in computer science.