int n=(int)(Math.random()*m) 如果m=1000000时，这时n 的范围为多大呀？ 它可能产生 7 吗 ？

(int)(Math.random())产生的范围是不是[0，1)之间呀？

There is a gerneral formular to do this, say if we want the interval between a and b(inclusive,b>a), then

int i = (int)(Math.random()*(b-a+1)+a);

more general, we have

int ranNum = (int)(Math.random()*(upperBound-lowerBound+1)+lowerBound);

in the example above, this range should be 0<= n < 1000000, another word 0<= n <= 999999

谢谢老大了

there is a class about random : java.util.Random

you can use it as this : Random rd = new Random();

rd.nextInt(int ceil);

then it will generate a value form 0 to ceil-1.(including 0 and ceil)