Random nextInt
public int nextInt(int n)返回壹個偽隨機數,它是取自此隨機數生成器序列的、在 0(包括)和指定值(不包括)之間均勻分布的 int 值。
源碼如下:
public int nextInt(int n) {
if (n<=0)
throw new IllegalArgumentException("n must be positive");
if ((n & -n) == n) // i.e., n is a power of 2
return (int)((n * (long)next(31)) >> 31);
int bits, val;
do {
bits = next(31);
val = bits % n;
} while(bits - val + (n-1) < 0);
return val;
}