Generate an array of random, non repeating numbers

RandomNumbers.java

private int[] randomNumbers( int size ) {
    int[] out = new int[ size ];

    ArrayList<Integer> allNumbers = new ArrayList<>();
    for ( int i = 1; i < 11000; i++ ) {
        allNumbers.add( i );
    }
    Collections.shuffle( allNumbers );

    for ( int i = 0; i < size; i++ ) {
        out[ i ] = allNumbers.get( i );
    }
    return out;
}