Why does this code using random strings print "hello world"?

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

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.