ArrayList Declaration vs Conversion

Question

I'm fairly out of touch with my Java programming and am doing Google's Udacity course as a refresher. I was going through lesson 1 on the Sunshine app where the lecturer chose to create fake data by declaring an array of strings and then converting it to an ArrayList.

The code is the following:

String[] data = {
            "Mon 6/23 - Sunny - 31/17",
            "Tue 6/24 - Foggy - 21/8",
            "Wed 6/25 - Cloudy - 22/17",
            "Thurs 6/26 - Rainy - 18/11",
            "Fri 6/27 - Foggy - 21/10",
            "Sat 6/28 - TRAPPED IN WEATHERSTATION - 23/18",
            "Sun 6/29 - Sunny - 20/7"
    };
    List<String> weatherForecast = new ArrayList<>(Arrays.asList(data));

I was wondering is there any advantage to using this convertion method? Why not just immediately declare the data as an ArrayList as such:

    ArrayList weatherForecast = new ArrayList();
    weatherForecast.add("Today - Sunny - 88/63");
    weatherForecast.add("Tomorrow - Foggy = 70/46");
    weatherForecast.add("Weds - Cloudy - 72/63");
    weatherForecast.add("Thurs 6/26 - Rainy - 18/11");
    weatherForecast.add("Sat 6/28 - TRAPPED IN WEATHERSTATION - 23/18");
    weatherForecast.add("Sun 6/29 - Sunny - 20/7");

Thanks!

Answer 1

The "normal" way would be to use a third form:

List<String> weatherForecast = new ArrayList<>();
Collections.addAll(weatherForecast,
        "Mon 6/23 - Sunny - 31/17",
        "Tue 6/24 - Foggy - 21/8",
        "Wed 6/25 - Cloudy - 22/17",
        "Thurs 6/26 - Rainy - 18/11",
        "Fri 6/27 - Foggy - 21/10",
        "Sat 6/28 - TRAPPED IN WEATHERSTATION - 23/18",
        "Sun 6/29 - Sunny - 20/7");

List is an interface, using that will enable to use another implementaton class like LinkedList (for just a couple of elements). Also useful as parameter type.

This uses the Collections utility class to add varargs ... strings. And uses under the hood a String[] for those args.

The .asList of the first option would be sufficient to have a List<String> not to be added to.

Answer 2

First approach :

• Better readability (can be even better, see my alternative); all datas are separated directly by comma instead of having a method call to add each one.
• Arrays.asList Create a fixed-size list for the given specific array using it internal ArrayList class which is just a wrapper around the array itself that make it more efficient then creating a full copy of the array.
• You keep the data in a List variable instead of an ArrayList variable which gives you more flexibility.

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Second approach :

• You are using raw types, it's bad at the beginning.
• No advantages.

Please if you use that approach, at least declare your List in a generic manner :

ArrayList<String> weatherForecast = new ArrayList<>();

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Alternative :

Note that you could directly do :

List<String> weatherForecast = Arrays.asList(
    "Mon 6/23 - Sunny - 31/17",
    "Tue 6/24 - Foggy - 21/8",
    "Wed 6/25 - Cloudy - 22/17",
    "Thurs 6/26 - Rainy - 18/11",
    "Fri 6/27 - Foggy - 21/10",
    "Sat 6/28 - TRAPPED IN WEATHERSTATION - 23/18",
    "Sun 6/29 - Sunny - 20/7"
);