我正在实现 simulated annealing (SA) 算法,我需要在其中复制状态(例如,记住到目前为止的最佳解决方案)。
我实现了一个复制方法,因为不鼓励使用 java 的 clone()
。
SA 是一种启发式算法,因此下一步采取的步骤是随机确定的。这是通过使用 Random
对象完成的,我也想复制它。
虽然算法没有要求,但我希望副本具有完全相同的状态。 但这只是这种情况,如果我在对象创建后直接进行“复制”并使用相同的种子对其进行初始化。
但如果我在复制过程之前对随机数执行一些操作,Random
对象的内在状态(即种子)会发生变化,并且复制行为会有所不同。
那么我怎样才能获得 java.util.Random
实例的精确副本?
示例
public class State
{
private final Random r;
private final long seed;
private Object currentOperand;
public State()
{
this(System.nanoTime(), null);
}
private State(long seed, Object currentOperand)
{
this.seed = seed;
this.r = new Random(seed);
this.currentOperand = currentOperand;
}
public State copy()
{
return new State(seed, currentOperand);
}
public void doSth()
{
/* operation with random operand */
currentOperand = r.nextInt(100);
}
public void redo()
{
// redo then set to null
currentOperand = null;
}
/* for completeness' sake... since it's simulated annealing */
public int computeEnergy() { return 0; }
}
最佳答案
我想出了一个自己的解决方案。它主要覆盖 Random
中的 next()
(因为所有其他方法都依赖于该方法),以及其他一些东西以保持一致性。
它提供调用此方法的实例的精确副本(制作随机实例的副本是否有意义是另一个主题...^^)。它的行为应该完全像它的父类(super class),至少那是我的意图。
请随意添加您的想法!
因为其他问题是关于获取种子的:可以轻松地向我的解决方案添加 getSeed()
方法。或 getInitialSeed()
, getCurrentSeed()
。
/* Bounded parameter type since a class that implements this interface
* should only be able to create copies of the same type (or a subtype).
*/
public interface Copyable<T extends Copyable<T>>
{
public T copy();
}
public class CopyableRandom extends Random implements Copyable<CopyableRandom>
{
private final AtomicLong seed = new AtomicLong(0L);
private final static long multiplier = 0x5DEECE66DL;
private final static long addend = 0xBL;
private final static long mask = (1L << 48) - 1;
public CopyableRandom() { this(++seedUniquifier + System.nanoTime()); }
private static volatile long seedUniquifier = 8682522807148012L;
public CopyableRandom(long seed) { this.seed.set((seed ^ multiplier) & mask); }
/* copy of superclasses code, as you can seed the seed changes */
@Override
protected int next(int bits)
{
long oldseed, nextseed;
AtomicLong seed_ = this.seed;
do
{
oldseed = seed_.get();
nextseed = (oldseed * multiplier + addend) & mask;
} while (!seed_.compareAndSet(oldseed, nextseed));
return (int) (nextseed >>> (48 - bits));
}
/* necessary to prevent changes to seed that are made in constructor */
@Override
public CopyableRandom copy() { return new CopyableRandom((seed.get() ^ multiplier) & mask); }
public static void main(String[] args)
{
CopyableRandom cr = new CopyableRandom();
/* changes intern state of cr */
for (int i = 0; i < 10; i++)
System.out.println(cr.nextInt(50));
Random copy = cr.copy()
System.out.println("\nTEST: INTEGER\n");
for (int i = 0; i < 10; i++)
System.out.println("CR\t= " + cr.nextInt(50) + "\nCOPY\t= " + copy.nextInt(50) + "\n");
Random anotherCopy = (copy instanceof CopyableRandom) ? ((CopyableRandom) copy).copy() : new Random();
System.out.println("\nTEST: DOUBLE\n");
for (int i = 0; i < 10; i++)
System.out.println("CR\t= " + cr.nextDouble() + "\nA_COPY\t= " + anotherCopy.nextDouble() + "\n");
}
}
这里是主要方法的输出:
19
23
26
37
41
34
17
28
29
6
TEST: INTEGER
CR = 3
COPY = 3
CR = 18
COPY = 18
CR = 25
COPY = 25
CR = 9
COPY = 9
CR = 24
COPY = 24
CR = 5
COPY = 5
CR = 15
COPY = 15
CR = 5
COPY = 5
CR = 30
COPY = 30
CR = 26
COPY = 26
TEST: DOUBLE
CR = 0.7161924830704971
A_COPY = 0.7161924830704971
CR = 0.06333509362539957
A_COPY = 0.06333509362539957
CR = 0.6340753697524675
A_COPY = 0.6340753697524675
CR = 0.13546677259518425
A_COPY = 0.13546677259518425
CR = 0.37133033932410586
A_COPY = 0.37133033932410586
CR = 0.796277965335522
A_COPY = 0.796277965335522
CR = 0.8610310118615391
A_COPY = 0.8610310118615391
CR = 0.793617231340077
A_COPY = 0.793617231340077
CR = 0.3454111197621874
A_COPY = 0.3454111197621874
CR = 0.25314618087856255
A_COPY = 0.25314618087856255
我还进行了一项测试,将 CopyableRandom 与 Random 进行了比较。它产生了相同的结果。
long seed = System.nanoTime();
Random cr = new CopyableRandom(seed);
Random cmp = new Random(seed);
关于java - 复制 java.util.Random 类型的实例变量以创建相同状态的对象,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/18493319/