我如何转换 arraylist<string> 至 arraylist<integer></integer></string>

Question

My goal is to find on which specific index is String from ArrayList and add them to new ArrayList, So if house is [0] than i want to return new ArrayList with integer.

public class List {
public static void main(String[] List) {
    List<String> words = new ArrayList<>();
    words.addAll(Arrays.asList("house", "bike","dog","house","house"));
    System.out.println(getIntegerArray(words,house));


 public static List<Integer> getIntegerArray(List<String> words, String word) {
        List<Integer> numbers = new ArrayList<>();
        for (int i = 0; i < numbers.size() ; i++) {

        }

At the begging I have ArrayList like this Input:

["house", "bike","dog"]

And I want to get new ArrayList like this Output:

[0,1,2]

Answer 1

You can do it just by checking if the string passed to the method is contained in the list and adding the number to the List numbers .

Here an example of the method getIntegerArray :

public static List<Integer> getIntegerArray(List<String> words, String word) {
    List<Integer> numbers = new ArrayList<>();

    for (int i=0; i < words.size() ; i++) {
        if (word.equals(words.get(i)))
            numbers.add(i);
    }
    return numbers;
}

PS: in System.out.println(getIntegerArray(words, house)); you are passing a variable house which is not declared. Probably you wanted to write "house" .

Answer 2

You should not worry about the size of numbers list, just add appropriate indexes as needed:

public static List<Integer> getIntegerArray(List<String> words, String word) {
    List<Integer> numbers = new ArrayList<>();
    for (int i = 0, n = words.size(); i < n; i++) {
        if (Objects.equals(word, words.get(i)))
            numbers.add(i);
    }
    return numbers;
}

---

Or use Stream API to get the list of indexes:

public static List<Integer> getIntegerArray(List<String> words, String word) {
    return IntStream.range(0, words.size())
        .filter(i -> Objects.equals(word, words.get(i)))
        .boxed()
        .collect(Collectors.toList());
}

Answer 3

getIntegerArray(List<String> words, String word) with a single word can't get you a list of integers with more than one element, I suggest passing the entire String[] , called findwords in the code below. Otherwise, lists have a indexOf() , which makes things really simple:

public static void main (String[] args) {
    List<String> words = new ArrayList<>();
    words.addAll(Arrays.asList("house", "bike","dog","house","house"));
    System.out.println(getIntegerArray(words,args));
}

public static List<Integer> getIntegerArray(List<String> words, String[] findwords) {
    List<Integer> numbers = new ArrayList<>();
    for(String word: findwords)
        numbers.add(words.indexOf(word));
    return numbers;
}

This will produce [0, 1, 2] as output when run with command line arguments house bike dog . See https://ideone.com/gYefsa (ideone doesn't support passing command line arguments, so args is just initialized inside the code).