您應該能夠使用反射此:
seed: 25214903916
mask: 281474976710655
multiplier: 25214903917
restored initial seed: 1
當seed
設置,該值被擾亂:
Random r = new Random(1);
Field f;
try {
f = r.getClass().getDeclaredField("seed");
f.setAccessible(true);
AtomicLong seed = (AtomicLong) f.get(r);
System.out.println("seed: " + seed);
f = r.getClass().getDeclaredField("mask");
f.setAccessible(true);
Long mask = (Long) f.get(r);
System.out.println("mask: " + mask);
f = r.getClass().getDeclaredField("multiplier");
f.setAccessible(true);
Long multiplier = (Long) f.get(r);
System.out.println("multiplier: " + multiplier);
long initialSeed = (seed.longValue()^multiplier);
System.out.println("restored initial seed: " + initialSeed);
} catch (NoSuchFieldException e1) {
} catch (SecurityException e2) {
} catch (IllegalAccessException e3) {
} catch (IllegalArgumentException e4) {
}
我的機器上輸出
public Random(long seed) {
if (getClass() == Random.class)
this.seed = new AtomicLong(initialScramble(seed));
else {
// subclass might have overriden setSeed
this.seed = new AtomicLong();
setSeed(seed);
}
}
private static long initialScramble(long seed) {
return (seed^multiplier) & mask; // (seed XOR multiplier) AND mask
}
然而,mask
和multiplier
只是定義爲:
private static final long mask = (1L << 48) - 1;
private static final long multiplier = 0x5DEECE66DL;
由於mask
是所有1
S爲最顯著48位,而XOR是可逆的,你可以回到最初的種子,如果(且僅當!)是小於(1L < < 48)的,即2^48:
輸出爲:
Random r = new Random((1L << 48)-1);
seed: 281449761806738
mask: 281474976710655
multiplier: 25214903917
restored initial seed: 281474976710655
和用於:
Random r = new Random((1L << 48));
seed: 25214903917
mask: 281474976710655
multiplier: 25214903917
restored initial seed: 0
另請參見this answer on StackOverflow
「getLong」在哪裏閱讀過?另外,你的意思是第一次調用getInt或任意調用? –
http://stackoverflow.com/questions/15236151/inverse-function-of-javas-random-function 然後調用不帶參數的getInt()2次 – mcat