import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Random;
import java.util.Set;import com.google.common.collect.Maps;public class RandomUtils {private static Random random;//双重校验锁获取一个Random单例public static Random getRandom() {if(random==null){synchronized (RandomUtils.class) {if(random==null){random =new Random();}}}return random;}/*** 获得一个[0,max)之间的整数。* @param max* @return*/public static int getRandomInt(int max) {return Math.abs(getRandom().nextInt())%max;}/*** 获得一个[0,max)之间的整数。* @param max* @return*/public static long getRandomLong(long max) {return Math.abs(getRandom().nextInt())%max;}/*** 从list中随机取得一个元素* @param list* @return*/public static <E> E getRandomElement(List<E> list){return list.get(getRandomInt(list.size()));}/*** 从set中随机取得一个元素* @param set* @return*/public static <E> E getRandomElement(Set<E> set){int rn = getRandomInt(set.size());int i = 0;for (E e : set) {if(i==rn){return e;}i++;}return null;}/*** 从map中随机取得一个key* @param map* @return*/public static <K,V> K getRandomKeyFromMap(Map<K,V> map) {int rn = getRandomInt(map.size());int i = 0;for (K key : map.keySet()) {if(i==rn){return key;}i++;}return null;}/*** 从map中随机取得一个value* @param map* @return*/public static <K,V> V getRandomValueFromMap(Map<K,V> map) {int rn = getRandomInt(map.size());int i = 0;for (V value : map.values()) {if(i==rn){return value;}i++;}return null;}public static void main(String[] args) {Set<Integer> set = new HashSet<>();for (int i = 0; i < 12; i++) {set.add(i);}for (int i = 0; i < 10; i++) {System.out.println(getRandomElement(set));}}
}