10

Suppose I have a string "1 23 40 187 298". This string only contains integers and spaces. How can I convert this string to an integer array, which is [1,23,40,187,298]. this is how I tried

public static void main(String[] args) {
    String numbers = "12 1 890 65";
    String temp = new String();
    int[] ary = new int[4];
    int j=0;
    for (int i=0;i<numbers.length();i++)
    {

        if (numbers.charAt(i)!=' ')
            temp+=numbers.charAt(i);
        if (numbers.charAt(i)==' '){
            ary[j]=Integer.parseInt(temp);
            j++;
        }
    }
}

but it doesn't work, please offer some help. Thank you!

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3
  • Use numbers.split(" "); first, so you have an array of strings and then you can convert them to int's Commented Mar 23, 2015 at 20:13
  • Have a look at this nice tutorial on the extremely useful split(..) method: tutorialspoint.com/java/java_string_split.htm Commented Mar 23, 2015 at 20:13
  • 1
    String[]nums = numbers.split(" ") Example: numbers = "1 23 40 187 298"; Then nums = {"1", "23", "40", "187", "298"}; Then you can do the following: int[] arrayOfIntegers = new int[nums.length]; for (int i = 0; i < nums.length; i++) { arrayOfIntegers[i] = Integer.parseInt(nums[i]); } Commented Mar 23, 2015 at 20:17

5 Answers 5

Reset to default
15

You are forgetting about

  • resetting temp to empty string after you parse it to create place for new digits

  • that at the end of your string will be no space, so 

    if (numbers.charAt(i) == ' ') {
    ary[j] = Integer.parseInt(temp);
    j++;
}

    will not be invoked, which means you need invoke

    ary[j] = Integer.parseInt(temp);

    once again after your loop

But simpler way would be just using split(" ") to create temporary array of tokens and then parse each token to int like

String numbers = "12 1 890 65";
String[] tokens = numbers.split(" ");
int[] ary = new int[tokens.length];

int i = 0;
for (String token : tokens){
    ary[i++] = Integer.parseInt(token); 
}

which can also be shortened with streams added in Java 8:

String numbers = "12 1 890 65";
int[] array = Stream.of(numbers.split(" "))
                    .mapToInt(token -> Integer.parseInt(token))
                    .toArray();

Other approach could be using Scanner and its nextInt() method to return all integers from your input. With assumption that you already know the size of needed array you can simply use 

String numbers = "12 1 890 65";
int[] ary = new int[4];

int i = 0;
Scanner sc = new Scanner(numbers);
while(sc.hasNextInt()){
    ary[i++] = sc.nextInt();
}
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5 Comments

Can you please update your answer for Java 8+ using streams?
@taurus05 Stream-based solution is already mentioned at the end of current answer: Stream.of(numbers.split(" ")).mapToInt(token -> Integer.parseInt(token)).toArray().
@taurus05 I moved stream-based solution up right under loop-based solution so people new to it would have better understanding about idea behind it. Hope now it is better visible.
Or just mapToInt(Integer::parseInt).
@MCEmperor Yes, and in real world I would probably use your approach, but since this question seems about quite basic issue I am assuming it is intended for Java newbies so I will stay with lambda since IMO it is easier to understand than method-references. Anyway thanks for mentioning about it :)
7

For java 8+ you can use this way:

final Integer[] ints = Arrays.stream(numbers.split(" "))
        .map(Integer::parseInt)
        .toArray(Integer[]::new);

or, if you need primitive ints, you can use this:

final int[] ints = Arrays.stream(numbers.split(" "))
        .mapToInt(Integer::parseInt)
        .toArray();
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3 Comments

are you sure this will work with a jdk earlier than 8 ? If my memory didn't fail me , map function and passing functions as arguments are only available in java-8.
thanks esin88, your answer is elegant but we must consider some OPs who don't have the newest version of something
yeah, but when i answered there already was an answer for java 7 and earlier :)
0

Reset the tmp String to "" after you parse the integer unless you wish to continue to append all the numbers of the String together. There are also alternatives as well - for instance splitting the String into an array on the space characeter, and then parsing the numbers individually

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0

Try this out,

public static void main(String[] args) {
    String numbers = "12 1 890 65";
    String[] parts = numbers.split(" ");

    int[] ary = new int[4];
    int element1 = Integer.parseInt(parts[0]);
    int element2 = Integer.parseInt(parts[1]);
    int element3 = Integer.parseInt(parts[2]);
    int element4 = Integer.parseInt(parts[3]);

    ary[0] = element1;
    ary[1] = element2;
    ary[2] = element3;
    ary[3] = element4;

    for(int i=0; i<4; i++){
        System.out.println(ary[i]);
    }

}
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0

I met similar question in android development. I want to convert a long string into two array -String array xtokens and int array ytokens. 

String result = "201 5 202 8 203 53 204 8";             
String[] tokens = result.split(" ");
String[] xtokens = new String[tokens.length/2 + 1];
int[] ytokens = new int[tokens.length/2 + 1];

for(int i = 0, xplace = 0, yplace = 0; i<tokens.length; i++){
    String temptoken = new String(tokens[i]);
    if(i % 2 == 0){
        xtokens[xplace++] = temptoken;
    }else {
        ytokens[yplace++] = Integer.parseInt(temptoken);
    }
}

You can first convert this string into an string array separated by space, then convert it to int array.

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