How to get list of Integer from String

Question

my string contains Integer separated by space:

String number = "1 2 3 4 5 "

How I can get list of Integer from this string ?

Answer 1

You can use a Scanner to read the string one integer at a time.

Scanner scanner = new Scanner(number);
List<Integer> list = new ArrayList<Integer>();
while (scanner.hasNextInt()) {
    list.add(scanner.nextInt());
}

Answer 2

ArrayList<Integer> lst = new ArrayList<Integer>();
for (String field : number.split(" +"))
    lst.add(Integer.parseInt(field));

With Java 8+:

List<Integer> lst = 
    Arrays.stream(number.split(" +")).map(Integer::parseInt).collect(Collectors.toList());

Answer 3

String number = "1 2 3 4 5";
String[] s = number.split("\\s+");

And then add it to your list by using Integer.parseInt(s[index]);

List<Integer> myList = new List<Integer>();
for(int index = 0 ; index<5 ; index++)
             myList.add(Integer.parseInt(s[index]);

Answer 4

In Java 8 you can use streams and obtain the conversion in a more compact way:

    String number = "1 2 3 4 5 ";
    List<Integer> x = Arrays.stream(number.split("\\s"))
            .map(Integer::parseInt)
            .collect(Collectors.toList());

Answer 5

Using Java8 Stream API map and mapToInt function you can archive this easily:

String number = "1 2 3 4 5";
List<Integer> x = Arrays.stream(number.split("\\s"))
        .map(Integer::parseInt)
        .collect(Collectors.toList());

or

String stringNum = "1 2 3 4 5 6 7 8 9 0";

List<Integer> poolList = Arrays.stream(stringNum.split("\\s"))
        .mapToInt(Integer::parseInt)
        .boxed()
        .collect(Collectors.toList());

Answer 6

用空格分割它，得到一个数组然后将其转换为列表。

Answer 7

Firstly,using split() method to make the String into String array.

Secondly,using getInteger() method to convert String to Integer.

Answer 8

 String number="1 2 3 4 5";
 List<Integer> l=new ArrayList<Integer>();
 String[] ss=number.split(" ");
 for(int i=0;i<ss.length;i++)
 {
   l.add(Integer.parseInt(ss[i]));
 }

System.out.println(l);

Answer 9

Simple solution just using arrays:

// variables
String nums = "1 2 3 4 5";
// can split by whitespace to store into an array/lits (I used array for preference) - still string
String[] num_arr = nums.split(" ");
int[] nums_iArr = new int[num_arr.length];
// loop over num_arr, converting element at i to an int and add to int array

for (int i = 0; i < num_arr.length; i++) {
    int num_int = Integer.parseInt(num_arr[i])
    nums_iArr[i] = num_int
}

That pretty much covers it. If you wanted to output them, to console for instance:

// for each loop to output
for (int i : nums_iArr) {
      System.out.println(i);
}

Answer 10

I would like to introduce tokenizer class to split by any delimiter. Input string is scanned only once and we have a list without extra loops.

    String value = "1, 2, 3, 4, 5";
    List<Long> list=new ArrayList<Long>();
    StringTokenizer tokenizer = new StringTokenizer(value, ",");
    while(tokenizer.hasMoreElements()) {
        String val = tokenizer.nextToken().trim();
        if (!val.isEmpty()) list.add( Long.parseLong(val) );
    }

Answer 11

You can split it and afterwards iterate it converting it into number like:

    String[] strings = "1 2 3".split("\\ ");
    int[] ints = new int[strings.length];
    for (int i = 0; i < strings.length; i++) {
        ints[i] = Integer.parseInt(strings[i]);
    }
    System.out.println(Arrays.toString(ints));

Answer 12

You first split your string using regex and then iterate through the array converting every value into desired type.

String[] literalNumbers = [number.split(" ");][1]
int[] numbers = new int[literalNumbers.length];

for(i = 0; i < literalNumbers.length; i++) {
    numbers[i] = Integer.valueOf(literalNumbers[i]).intValue();
}

Answer 13

I needed a more general method for retrieving the list of integers from a string so I wrote my own method. I'm not sure if it's better than all the above because I haven't checked them. Here it is:

public static List<Integer> getAllIntegerNumbersAfterKeyFromString(
        String text, String key) throws Exception {
    text = text.substring(text.indexOf(key) + key.length());
    List<Integer> listOfIntegers = new ArrayList<Integer>();
    String intNumber = "";
    char[] characters = text.toCharArray();
    boolean foundAtLeastOneInteger = false;
    for (char ch : characters) {
        if (Character.isDigit(ch)) {
            intNumber += ch;
        } else {
            if (intNumber != "") {
                foundAtLeastOneInteger = true;
                listOfIntegers.add(Integer.parseInt(intNumber));
                intNumber = "";
            }
        }
    }
    if (!foundAtLeastOneInteger)
        throw new Exception(
                "No matching integer was found in the provided string!");
    return listOfIntegers;
}

The @key parameter is not compulsory. It can be removed if you delete the first line of the method:

    text = text.substring(text.indexOf(key) + key.length());

or you can just feed it with "".