自制随机数生成类（Java语言描述）

思路

31位，线性同余生成随机数……

可以使用默认种子值或者指定种子值来生成随机数。

核心功能

• int randomInt() → Uniform, 1 to 2³¹-1
• int random0_1() → Uniform, 0 to 1
• int randomInt(int low, int high) → Uniform, low…high
• long randomLong(long low, long high) → Uniform, low…high
• void permute(Object [] a) → Randomly permutate

Random类的编程实现

/**
 * Random number class, using a 31-bit linear congruential generator.
 */
public class Random {

    private static final int A = 48271;
    private static final int M = 2147483647;
    private static final int Q = M / A;
    private static final int R = M % A;

    private int state;

    /**
     * Construct this Random object with
     * initial state obtained from system clock.
     */
    public Random() {
        this((int)(System.currentTimeMillis() % Integer.MAX_VALUE));
    }

    /**
     * Construct this Random object with
     * specified initial state.
     * @param initialValue the initial state.
     */
    public Random(int initialValue) {
        if(initialValue < 0) {
            initialValue += M;
        }
        state = initialValue;
        if(state == 0) {
            state = 1;
        }
    }

    /**
     * Return a pseudorandom int, and change the
     * internal state.
     * @return the pseudorandom int.
     */
    public int randomInt() {
        int tmpState = A * (state % Q) - R * (state / Q);
        if(tmpState >= 0) {
            state = tmpState;
        } else {
            state = tmpState + M;
        }
        return state;
    }

    /**
     * Return a pseudorandom int, and change the
     * internal state. DOES NOT WORK.
     * @return the pseudorandom int.
     */
    public int randomIntWRONG() {
        return state = (A * state) % M;
    }

    /**
     * Return a pseudorandom double in the open range 0..1
     * and change the internal state.
     * @return the pseudorandom double.
     */
    public double random0_1() {
        return (double) randomInt() / M;
    }

    /**
     * Return an int in the closed range [low,high], and
     * change the internal state.
     * @param low the minimum value returned.
     * @param high the maximum value returned.
     * @return the pseudorandom int.
     */
    public int randomInt(int low, int high) {
        double partitionSize = (double) M / (high-low+1);
        return (int) (randomInt() / partitionSize) + low;
    }

    /**
     * Return an long in the closed range [low,high], and
     * change the internal state.
     * @param low the minimum value returned.
     * @param high the maximum value returned.
     * @return the pseudorandom long.
     */
    public long randomLong(long low, long high) {
        long longVal =  ((long) randomInt() << 31) + randomInt();
        long longM =  ((long) M << 31) + M;
        double partitionSize = (double) longM / (high-low+1);
        return (long) (longVal / partitionSize) + low;
    }

    /**
     * Randomly rearrange an array.
     * The random numbers used depend on the time and day.
     * @param a the array.
     */
    public static void permute(Object [] a) {
        Random r = new Random();
        for(int j = 1; j < a.length; j++) {
            Sort.swapReferences(a, j, r.randomInt(0, j));
        }
    }

}

测试

public class RandomTest {
    public static void main(String [] args) {
        Random r = new Random(1);
        for(int i = 0; i < 20; i++) {
            System.out.println(r.randomInt());
        }
    }
}

一则测试结果：

48271
182605794
1291394886
1914720637
2078669041
407355683
1105902161
854716505
564586691
1596680831
192302371
1203428207
1250328747
1738531149
1271135913
1098894339
1882556969
2136927794
1559527823
2075782095