[JAVA]数组 求代码解释

求代码解释

public class CouponCollector {
public static void main(String[] args) {
int N = Integer.parseInt(args[0]);

boolean[] found = new boolean[N];

int cardcnt = 0;

int valcnt = 0;

    while (valcnt < N) {
        int val = (int) (Math.random() * N);   
        cardcnt++;                             
        if (!found[val]) valcnt++;             
        found[val] = true;                    
    }


    System.out.println(cardcnt);
}

}