Clash Royale CLAN TAG#URR8PPP

how to find all occurrence with indexes of string in an ArrayList java

Having an ArrayList with data like below. My requirement is to find all the indexes where length of data is 4.

values.add("1000");
values.add("10001111");
values.add("45678901");
values.add("1111");
values.add("22222222");
values.add("2222");
values.add("33333333");


3 Answers
3

You need to :

Workable demo : Using Streams you can inline the solution to obtain a List or a int

Workable demo

Streams

List

int

List<Integer> indexes = values.stream().filter(s -> s.length() == 4)
.map(values::indexOf)
.collect(Collectors.toList());

int indexesArray = values.stream().filter(s -> s.length() == 4)
.mapToInt(values::indexOf)
.toArray();


Workable demo : Using a classic for loop

Workable demo

for loop

List<Integer> indexes = new ArrayList<>();
for(int i=0; i<values.size(); i++)
if(values.get(i).length() == 4)
indexes.add(i);




You can store the matching values and its indices/indexes in a Map<Integer, String> when you iterate over the values and output the content of that Map afterwards:

Map<Integer, String>

values

Map

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Test

public static void main(String args)
List<String> values = new ArrayList<String>();

values.add("1000");
values.add("10001111");
values.add("45678901");
values.add("1111");
values.add("22222222");
values.add("2222");
values.add("33333333");

// create a storage structure for index and value
Map<Integer, String> valuesWithLengthFour = new HashMap<Integer, String>();

// iterate over your list in order to get all the matching values and indexes
for (int i = 0; i < values.size(); i++)
String value = values.get(i);
if (value.length() == 4)
valuesWithLengthFour.put(i, value);



System.out.println("The following matching values were found in "values":");

// print out the content of the storage structure
for (int key : valuesWithLengthFour.keySet())
System.out.println("Index: " + key + ", Value: " + valuesWithLengthFour.get(key));





There are different ways to achieve this... For a one liner, try out the code @Lino stated in one of the comments below your question.

You can create an IntStream of indices:

IntStream

IntStream allIndices = IntStream.range(0, values.size());


Which you then can filter, by the condition you provided:

IntStream filteredIndices = allIndices.filter(i -> values.get(i).length() == 4);


Finally you can transform those indices into any dataStructure you like.

An array:

int indices = filteredIndices.toArray();


Or a List

List<Integer> indices = filteredIndices.boxed().collect(Collectors.toList());


As one statement:

int indices = IntStream.range(0, values.size())
.filter(i -> values.get(i).length() == 4)
.toArray();


By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service, privacy policy and cookie policy, and that your continued use of the website is subject to these policies.