Print only those numbers that are double of another number in the array in Java

Question

I'm practicing algorithms and let's say we have an array with elements 2, 3, 9, 12, 7, 18, then I want to print 18 only because it's double of 9. When I print the result it always displays much more lines, however, the printed numbers (if there are any) are good. How can I manage displaying the result properly? (Using only arrays.) I know it's a silly question but I tried so many ways and it was only worse.

Now, it shows me this for example (140 is correct, but the other line are not needed):

The following number is doubled of another number from the array: 0
The following number is doubled of another number from the array: 0
The following number is doubled of another number from the array: 140
The following number is doubled of another number from the array: 0
The following number is doubled of another number from the array: 0

My code:

public class DoubleNums {

    public static void main(String[] args) {

        Random random = new Random();

        int[] array = new int[50];
        int[] even;
        int[] doubleNum;
        int count = 0;
        int doubles = 0;

        for (int i = 0; i < array.length; i++) {
            array[i] = random.nextInt(200);
            System.out.println(array[i] + " ");
        }
        for (int j = 0; j < array.length; j++) { 
            even = new int[array.length];
            if (array[j] % 2 == 0) {
                even[count] = array[j];
                count++;
            }
            for (int k = 0; k < array.length; k++) {
                doubleNum = new int[array.length];
                if (array[j] / 2 == array[k]) {
                    even[doubles] = k;
                    doubles++;
                    System.out.println("The following number is doubled of another number from the array: " + even[doubles]);               
                }                
            }               
        }
        System.out.println("Number of even nums: " + count);
        }
    }

Answer 1

Use a HashSet<Integer> to store double the value of each element:

Set<Integer> setOfArray = new HashSet<>();
for (int a : array) setOfArray.add(2 * a);

Then loop through the array again, looking for matching elements:

for (int a : array) {
  if (setOfArray.contains(a)) {
    System.out.println(a);
  }
}

Or

IntStream.of(array).boxed().filter(setOfArray::contains)
    .forEach(System.out::println);

Answer 2

This is a simple task: first, for each number n, store 2n in a set. Then, iterate through the numbers and check which of them is in the set.

import java.util.*;

public class DoubleNums {
    public static void main(String[] args) {
        int[] numbers = new int[]{2, 3, 9, 12, 7, 18};   //original array

        HashSet<Integer> h = new HashSet<Integer>();     //set

        for(int i = 0; i < numbers.length; i++) h.add(numbers[i] * 2);
        for(int i = 0; i < numbers.length; i++){
            if(h.contains(numbers[i])) System.out.println(numbers[i]);
        }
    }
}

Complexity: O(n)

A HashSet<Integer> works like a simple set, but faster, because it uses properties of hash tables to add and find elements.