生成随机数

import java.text.DecimalFormat;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Random;

/**
 * 获取随机数
 *
 * @author
 *
 */
public class RandomUtils {

    private static final Random random = new Random();
    private static final DecimalFormat fourdf = new DecimalFormat("0000");
    private static final DecimalFormat sixdf = new DecimalFormat("000000");
    public static String getFourBitRandom() {
        return fourdf.format(random.nextInt(10000));
    }
    public static String getSixBitRandom() {
        return sixdf.format(random.nextInt(1000000));
    }

    /**
     * 给定数组，抽取n个数据
     * @param list
     * @param n
     * @return
     */
    public static ArrayList getRandom(List list, int n) {

        Random random = new Random();
        HashMap<Object, Object> hashMap = new HashMap<Object, Object>();
        // 生成随机数字并存入HashMap
        for (int i = 0; i < list.size(); i++) {
            int number = random.nextInt(100) + 1;
            hashMap.put(number, i);
        }
        // 从HashMap导入数组
        Object[] robjs = hashMap.values().toArray();
        ArrayList r = new ArrayList();
        // 遍历数组并打印数据
        for (int i = 0; i < n; i++) {
            r.add(list.get((int) robjs[i]));
            System.out.print(list.get((int) robjs[i]) + "\t");
        }
        System.out.print("\n");
        return r;
    }

    public static  String getRandom(){
        //Random类
        Random random=new Random();//随机生成器
        //范围在26个大小写字母，与10个数字之间
        char[] chars = new char[]{
                'a','b','c','d','e' ,'f','g','h','i','j','k' ,'m','n','p','q','r','s' ,'t','u','v','w','x','y' ,'z',
                'A','B','C','D','E' ,'F','G','H','J','K' ,'M','N','P','Q','R','S' ,'T','U','V','W','X','Y' ,'Z',
                '2','3','4','5','6','7','8','9'};
        String code ="";
        //遍历4次得到4个随机整数,再把随机整数作为数组下标得到对象的字符
        for(int i=0;i<4;i++){
            int index=random.nextInt(chars.length);//每次遍历生成数组长度范围内的随机整数
            //System.out.println(index);
            //生成数组中的随机整数作为下标得到对应的字符值，字符串加字符结果为字符串
            code+=chars[index];
        }
        return code;
    }
}