J2ME：如何生成随机数？

Question

I just wanted to know how do I generate random number using J2ME CLDC 1.0 MIDP 2.0 ?

Basically I want to generate a 14 digits random number each time when the menu item Generate is clicked from the mobile's screen.

Answer 1

I'm not really familiar with J2ME, however the Javadoc shows that the Random class is part of the CLDC api, so you can generate a 14 digit number like this:

public static void main(String[] args) {
    Random r = new Random();
    long l = r.nextLong();
    System.out.println(String.format("%015d", l).substring(1, 15));
}

Answer 2

Random r = new Random();
r.nextInt(bottomX-topX)+topX; //will give you the next random integer in range [bottomX,topX]

Answer 3

You can use the Random class of MIDP, or the one in CLDC 1.1

You could do nextLong and then truncate, or use next(44) and iterate from there to have a real 14-number long.

Answer 4

import java.util.Random;

private static void showRandomInteger(int aStart, int aEnd){
        Random generator = new Random();
        generator.setSeed(System.currentTimeMillis());
        if ( aStart > aEnd ) {
          throw new IllegalArgumentException("Start cannot exceed End.");
        }
        //get the range, casting to long to avoid overflow problems
        long range = (long)aEnd - (long)aStart + 1;
        // compute a fraction of the range, 0 <= frac < range
        long fraction = (long)(range * generator.nextDouble());
        int randomNumber =  (int)(fraction + aStart);
        System.out.println("Generated : " + randomNumber);
      }

you can use this general method for calculating random numbers in any range.