List<String> destList = Arrays.asList("foo"); List<String> newList = Arrays.asList("0", "1", "2", "3", "4", "5"); destList = Stream.concat(destList.stream(), newList.stream()).parallel() .collect(Collectors.toList()); System.out.println(destList); //output: [foo, 0, 1, 2, 3, 4, 5]