Java - Finding Multiple Modes In An Array [duplicate]

I'm trying to complete an assignment where I have to find the mode of a random array. I have figured out how to get the mode for a single number, although I do not know how to find the mode for multiple numbers. For example, if I had the array [2, 2, 3, 3, 4] the mode would be 2 and 3. Here is my code so far:

//Getting our random array
    Random r = new Random();
    int[] arr = new int[15];
    for(int i = 0; i < arr.length; i++) {
        arr[i] = r.nextInt(15, 51);
        System.out.print(arr[i]);
        if(i < arr.length -1)
        {
            System.out.print(", ");
        } else {
            System.out.println();
        }
    }


//Mode
    int maxnumber = -1;
    int maxappearances = -1;
    
    
    for (int i=0; i < arr.length; i++)
    {
        int count = 0;
        
        for (int j=0; j < arr.length; j++)
        {
            if(arr[i] == arr[j])
            {
                count++;
            }
            
        }
        if(count > maxappearances)
        {
            maxnumber = arr[i];
            maxappearances = count;
            count = -1; 
    }
    
    } 
System.out.println("The mode is "+ maxnumber);

Output:

15, 21, 21, 47, 46, 44, 49, 45, 29, 31, 16, 36, 19, 17, 20
The mode is 21

If I could get some help that would be great, thanks!