public static void main(String[] args) {
        HashSet<Integer> hashSet = new HashSet<>();
        Random random = new Random();
        for (int i = hashSet.size(); i < 50; i++) {
            hashSet.add(random.nextInt(9999));
        }
        System.out.println(hashSet);
    }

public class RandomArray {
    private static final int size = 30;             //随机数范围
    private static final int arrayLength = size - 10;     //数组长度
    private static int realSize = 0;                //数组有效数据长度
    public static void main(String[] args) {
        int[] arr = new int[arrayLength];
        randomArray(arr);
        sort(arr);
        print(arr);
    }

    private static void print(int[] arr) {      //打印
        for (int i = 0; i < realSize - 1; i++)
            System.out.print(arr[i] + ", ");
    }

    private static void randomArray(int[] arr) {
        while (realSize < arrayLength) {        //循环条件为数组实际长度（即有用数据）小于数组长度
            int randomNum = (int)(Math.random() * size + 1);
            sort(arr);          //插入之前排序作判断
            if (!isExists(arr, randomNum))          //如果存在，则跳过本次，否则存入数组
                arr[realSize++] = randomNum;
        }
    }

    private static void sort(int[] arr) {       //冒泡排序
        for (int start = 0; start < realSize; start++) {
            for (int end = start + 1; end < realSize; end++) {
                if (arr[start] > arr[end]) {
                    int temp = arr[start];
                    arr[start] = arr[end];
                    arr[end] = temp;
                }
            }
        }
    }

    private static boolean isExists(int[] arr, int num) {   //用二分法判断该数是否存在于该数组
        int start = 0, end = realSize - 1;
        while (start <= end) {
            int middle = (start + end) / 2;
            if (num > arr[middle])
                start = middle + 1;
            else if (num < arr[middle])
                end = middle - 1;
            else
                return true;
        }
        return false;
    }
}

public static void main(String[] args) {
		// TODO Auto-generated method stub

		HashSet<Integer>a = new HashSet<Integer>();
		while(true) {
			a.add((int) (Math.random()*9999));
			if(a.size()==50) {
				break;
			}
		}
		int i = 0;
		for(int each:a) {
			if(i%10==0&&i!=0) {
				System.out.println();
			}
			System.out.print(each+"\t");
			i++;
			
		}
	}

package collection;

import java.util.*;

public class TestCollection2 {
    public static void main(String[] args) {
        List<Integer> numbers = new ArrayList<>();
        HashSet<Integer> n = new HashSet<>();
        for(;;){
            int random  = (int)(Math.random()*10000);
            n.add(random);
            if(n.size() == 50)
                break;
        }
        System.out.println(n);
        System.out.println("共"+n.size()+"个");

    }
}

import java.util.HashSet;

public class TestCollection3 {

	public static void main(String[] args) {
		HashSet<Integer> numbers = new HashSet<Integer>();
		System.out.println(numbers.size());
		for(int i = 0;numbers.size() < 50;i++) {
			int j = (int)(Math.random()*10000
					+Math.random()*1000+Math.random()*100+Math.random()*100);
			numbers.add(j);
		}
		System.out.println(numbers.size());
		System.out.println(numbers);
	}

}

package test;

import java.util.HashSet;
import java.util.Random;

public class chongFu {
    public static void main(String[] args) {
        Random r = new Random();
        HashSet<Integer> hs = new HashSet<>(50);
        while (hs.add(r.nextInt(9999))) {}
        System.out.println(hs.toString());
    }
}