Printing certain values using Collections.frequency()

Question

I have an array as follows:

int[] array = {11, 14, 17, 11, 48, 33, 29, 11, 17, 22, 11, 48, 18};

What I wanted to do was to find the duplicate values, and print them.

So my way of doing this was to convert to ArrayList, then to Set and use a stream on the Set.

ArrayList<Integer> list = new ArrayList<>(array.length);
for (int i = 0; i < array.length; i++) {
    list.add(array[i]);
}

Set<Integer> dup = new HashSet<>(list);

I then used a stream to loop through it and print the values using Collections.frequency.

dup.stream().forEach((key) -> {
            System.out.println(key + ": " + Collections.frequency(list, key));
        });

Which will of course print them all, even if the count is one.

I thought adding in if(key > 1) but it's the value I want not the key.

How can I get the value in this instance to print only where value > 2.

I could probably put in:

int check = Collections.frequency(list, key);
            if (check > 1) {

but this then duplicates Collections.frequency(list, key) in the stream and is quite ugly.

Answer 1

Probably you can to use filter to get only the values great than 2 :

dup.stream()
       .filter(t -> Collections.frequency(list, t) > 2)
       .forEach(key -> System.out.println(key + ": " + Collections.frequency(list, key)));

result in your case is :

11: 4

---

Edit

Another solution :

No need to use a Set or Collections.frequency you can just use :

Integer[] array = {11, 14, 17, 11, 48, 33, 29, 11, 17, 22, 11, 48, 18};
Arrays.stream(array).collect(Collectors.groupingBy(p -> p, Collectors.counting()))
        .entrySet().stream().filter(t -> t.getValue() > 1)
        .forEach(key -> System.out.println(key.getKey() + ": " + key.getValue()));

Output

48: 2
17: 2
11: 4