JDK5.0 新機能：オートボクシング、実習課題

import java.util.*;

public class C2008081800 {
    public static void main(String[] args) {
        ArrayList<Double> a = new ArrayList<Double>();
        double sum = 0;
        int num = 1000;

        for (int i = 0; i < num; i++) {
            a.add(Math.random());
        }

        for (Double d : a) {
            sum += d;
        }
        System.out.println("sum: " + sum);
        System.out.println("ave: " + sum / num);
    }
}

で、

sum: 523.3770231011805
ave: 0.5233770231011805