您应该能够为此使用反射:
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) {
}
我机器上的输出:
seed: 25214903916
mask: 281474976710655
multiplier: 25214903917
restored initial seed: 1
设置时seed
,对值进行加扰:
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
andmultiplier
被定义为:
private static final long mask = (1L << 48) - 1;
private static final long multiplier = 0x5DEECE66DL;
由于最低有效 48 位的mask
全部1
为 s 并且 XOR 是可逆的,因此当(且仅当!)它小于 (1L << 48) 时,您可以取回初始种子,即 2^48:
输出:
Random r = new Random((1L << 48)-1);
seed: 281449761806738
mask: 281474976710655
multiplier: 25214903917
restored initial seed: 281474976710655
并为:
Random r = new Random((1L << 48));
seed: 25214903917
mask: 281474976710655
multiplier: 25214903917
restored initial seed: 0
另请参阅StackOverflow 上的此答案