public class test {    public static void main(String[] args) {                getRandomNum1();        getRandomNum2();        getRandomNum3();        getRandomNum4();        getRandomNum5();    }    /**     * 对数组里面的数字进行循环判断，如果有不做处理，继续循环。没有就添加。     */    private static void getRandomNum1() {        int [] arr = new int[5];          int count = 0;          while(count < 5) {              int num = (int) (Math.random() * (10)) ;              boolean flag = true;              for (int j = 0; j < 5; j++) {                  if(num == arr[j]){                      flag = false;                      break;                  }              }              if(flag){                  arr[count] = num;                  count++;              }          }         System.out.println("随机数1："+Arrays.toString(arr));    }    /**     * 判断是否存在。不在就添加，在就不处理。继续循环     */    private static void getRandomNum2() {        List list = new ArrayList();        while(list.size() < 5) {              int num = (int) (Math.random() * (10)) ;              if(!list.contains(num)) {                list.add(num);            }        }         System.out.println("随机数2："+Arrays.toString(list.toArray()));    }    /**     * 利用set特性.自动去重     */    private static void getRandomNum3() {        Set set = new TreeSet<>();        while(set.size() < 5) {              int num = (int) (Math.random() * (10)) ;              set.add(num);        }         System.out.println("随机数3："+Arrays.toString(set.toArray()));    }        /**     * 利用map特性做空判断     */    private static void getRandomNum4() {        Map map = new HashMap<>();        while(map.size() < 5) {              int num = (int) (Math.random() * (10)) ;              if(map.get(num) == null ) {                map.put(num,num);            }        }         System.out.println("随机数4："+map.values());    }    /**     * 批量生成随机数，取随机的5个     */    private static void getRandomNum5() {        int[] arrs = new int[20];           for (int i = 0; i < arrs.length; i++) {              arrs[i] = i ;        }          int[] arr = new int[5];          boolean[] flag = new boolean[arrs.length];          Random random=new Random();          int j = 0;        for (int i = 0; i < arr.length; i++) {              do {                  j = random.nextInt(flag.length);              } while (flag[j]);  //标记,如果取出来过就继续do while 只有不符合while才会继续            flag[j] = true;             arr[i]=arrs[j];          }         System.out.println("随机数5："+Arrays.toString(arr));    }}