## Why does this code using random strings print “hello world”?

2021-6-3 anglehua

The following print statement would print "hello world". Could anyone explain this?

``````System.out.println(randomString(-229985452) + " " + randomString(-147909649));
``````

And `randomString()` looks like this:

``````public static String randomString(int i)
{
Random ran = new Random(i);
StringBuilder sb = new StringBuilder();
while (true)
{
int k = ran.nextInt(27);
if (k == 0)
break;

sb.append((char)('`' + k));
}

return sb.toString();
}
``````

When an instance of `java.util.Random` is constructed with a specific seed parameter (in this case `-229985452` or `-147909649`), it follows the random number generation algorithm beginning with that seed value.

Every `Random` constructed with the same seed will generate the same pattern of numbers every time.

The other answers explain why, but here is how.

Given an instance of `Random`:

``````Random r = new Random(-229985452)
``````

The first 6 numbers that `r.nextInt(27)` generates are:

``````8
5
12
12
15
0
``````

and the first 6 numbers that `r.nextInt(27)` generates given `Random r = new Random(-147909649)` are:

``````23
15
18
12
4
0
``````

Then just add those numbers to the integer representation of the character ``` (which is 96):

``````8  + 96 = 104 --> h
5  + 96 = 101 --> e
12 + 96 = 108 --> l
12 + 96 = 108 --> l
15 + 96 = 111 --> o

23 + 96 = 119 --> w
15 + 96 = 111 --> o
18 + 96 = 114 --> r
12 + 96 = 108 --> l
4  + 96 = 100 --> d
``````