Convert an array to list with specific range in Java 8

user_4529026 0
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I want to convert one string array to list with specific range. In my case I always want from index 1 to last index. I don't need the index 0 value included in the list. Is there any direct method that I can use to filter and convert to the list as I need ?

public class test1 {

    public static void main(String[] args) {
        String[] optArr = {"start", "map1", "map2", "map3"};
        List<String> list = Arrays.stream(optArr).collect(Collectors.toList());
        System.out.println(list);
    }
}
java-8 java
9 Answers

You can also use the overloaded method Arrays.stream​(T[] array, int startInclusive, int endExclusive) as :

List<String> list = Arrays.stream(optArr, 1, optArr.length)
                          .collect(Collectors.toList());

Returns a sequential Stream with the specified range of the specified array as its source.

Alternatively(non Java-8), using the subList is an option, but I would prefer chaining it in one-line instead of creating a new object as:

List<String> list = Arrays.asList(optArr).subList(1, optArr.length);
user_17461180

You can use Stream.skip():

List<String> list = Arrays.stream(optArr).skip(1).collect(Collectors.toList());
user_35589600

One non Java 8 option might be to just create a view on top of your current list which omits the first element:

List<String> list = Arrays.stream(optArr).collect(Collectors.toList());
List<String> viewList = list.subList(1, list.size());

This would mean though that the underlying data structure is still the original list, but one extra element in memory does not seem like a big penalty.

user_18632290

One method use List.sublist(int,int)

List<String> list = Arrays.asList(optArr).subList(1,optArr.length);
System.out.println(list);

Second method use Stream

List<String> list = Arrays.stream(optArr)
    .skip(1)
    .collect(Collectors.toList());
System.out.println(list);
user_63759170
user_64935760

Looking at your data you might consider :

List<String> list = Stream.of(optArr).filter(s -> s.startsWith("map")).collect(toList());

But if you just want to filter the first index sublist is the way to go. You do not need to use stream wherever you can.

user_1847300

It should be like this.

List<String> al = new ArrayList<>(Arrays.asList(optArr));
List actualList = list.subList(1, al.size());
user_84274570

You can also use Arrays.copyOfRange to copy an array.

Copies the specified range of the specified array into a new array. The initial index of the range (from) must lie between zero and original.length, inclusive.

public static <T> T[] copyOfRange(T[] original, int from, int to)

And then convert into List

List<String> result = Arrays.asList(Arrays.copyOfRange(optArr, 1, optArr.length));

IntStream : one other way by using IntStream

List<String> result = IntStream.range(1, optArr.length).mapToObj(i->optArr[i]).collect(Collectors.toList());
user_99591520

Why do you need to use streams? Why isn't some ancient magic like for-loops enough for the task?

String[] optArr = {"start", "map1", "map2", "map3"};
final List<String> list = new ArrayList<>();

for (int i = 1; i < optArr.length; i++) // skip first element
    list.add(optArr[i]);

The simplest tool for the job.

user_85243010
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