为什么这段代码使用随机字符串打印"hello world"？

Question

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();
}

转载于:https://stackoverflow.com/questions/15182496/why-does-this-code-using-random-strings-print-hello-world

Answer 1

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.

Answer 2

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 0and the first 6 numbers that r.nextInt(27) generates given Random r = new Random(-147909649) are:23 15 18 12 4 0Then 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

Answer 3

I'll just leave it here. Whoever has a lot of (CPU) time to spare, feel free to experiment :) Also, if you have mastered some fork-join-fu to make this thing burn all CPU cores (just threads are boring, right?), please share your code. I would greatly appreciate it.public&nbsp;static&nbsp;void&nbsp;main(String[]&nbsp;args)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;long&nbsp;time&nbsp;=&nbsp;System.currentTimeMillis(); &nbsp;&nbsp;&nbsp;&nbsp;generate("stack"); &nbsp;&nbsp;&nbsp;&nbsp;generate("over"); &nbsp;&nbsp;&nbsp;&nbsp;generate("flow"); &nbsp;&nbsp;&nbsp;&nbsp;generate("rulez"); &nbsp;&nbsp;&nbsp;&nbsp;System.out.println("Took&nbsp;"&nbsp;+&nbsp;(System.currentTimeMillis()&nbsp;-&nbsp;time)&nbsp;+&nbsp;"&nbsp;ms"); } private&nbsp;static&nbsp;void&nbsp;generate(String&nbsp;goal)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;long[]&nbsp;seed&nbsp;=&nbsp;generateSeed(goal,&nbsp;Long.MIN_VALUE,&nbsp;Long.MAX_VALUE); &nbsp;&nbsp;&nbsp;&nbsp;System.out.println(seed[0]); &nbsp;&nbsp;&nbsp;&nbsp;System.out.println(randomString(seed[0],&nbsp;(char)&nbsp;seed[1])); } public&nbsp;static&nbsp;long[]&nbsp;generateSeed(String&nbsp;goal,&nbsp;long&nbsp;start,&nbsp;long&nbsp;finish)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;char[]&nbsp;input&nbsp;=&nbsp;goal.toCharArray(); &nbsp;&nbsp;&nbsp;&nbsp;char[]&nbsp;pool&nbsp;=&nbsp;new&nbsp;char[input.length]; &nbsp;&nbsp;&nbsp;&nbsp;label: &nbsp;&nbsp;&nbsp;&nbsp;for&nbsp;(long&nbsp;seed&nbsp;=&nbsp;start;&nbsp;seed&nbsp;<&nbsp;finish;&nbsp;seed++)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Random&nbsp;random&nbsp;=&nbsp;new&nbsp;Random(seed); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for&nbsp;(int&nbsp;i&nbsp;=&nbsp;0;&nbsp;i&nbsp;<&nbsp;input.length;&nbsp;i++) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;pool[i]&nbsp;=&nbsp;(char)&nbsp;random.nextInt(27); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if&nbsp;(random.nextInt(27)&nbsp;==&nbsp;0)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int&nbsp;base&nbsp;=&nbsp;input[0]&nbsp;-&nbsp;pool[0]; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for&nbsp;(int&nbsp;i&nbsp;=&nbsp;1;&nbsp;i&nbsp;<&nbsp;input.length;&nbsp;i++)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if&nbsp;(input[i]&nbsp;-&nbsp;pool[i]&nbsp;!=&nbsp;base) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;continue&nbsp;label; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return&nbsp;new&nbsp;long[]{seed,&nbsp;base}; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;throw&nbsp;new&nbsp;NoSuchElementException("Sorry&nbsp;:/"); } public&nbsp;static&nbsp;String&nbsp;randomString(long&nbsp;i,&nbsp;char&nbsp;base)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;System.out.println("Using&nbsp;base:&nbsp;'"&nbsp;+&nbsp;base&nbsp;+&nbsp;"'"); &nbsp;&nbsp;&nbsp;&nbsp;Random&nbsp;ran&nbsp;=&nbsp;new&nbsp;Random(i); &nbsp;&nbsp;&nbsp;&nbsp;StringBuilder&nbsp;sb&nbsp;=&nbsp;new&nbsp;StringBuilder(); &nbsp;&nbsp;&nbsp;&nbsp;for&nbsp;(int&nbsp;n&nbsp;=&nbsp;0;&nbsp;;&nbsp;n++)&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int&nbsp;k&nbsp;=&nbsp;ran.nextInt(27); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if&nbsp;(k&nbsp;==&nbsp;0) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;break; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;sb.append((char)&nbsp;(base&nbsp;+&nbsp;k)); &nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;return&nbsp;sb.toString(); }Output:-9223372036808280701 Using&nbsp;base:&nbsp;'Z' stack -9223372036853943469 Using&nbsp;base:&nbsp;'b' over -9223372036852834412 Using&nbsp;base:&nbsp;'e' flow -9223372036838149518 Using&nbsp;base:&nbsp;'d' rulez Took&nbsp;7087&nbsp;ms