Converting a String array into an int Array in java

Question

I am new to java programming. My question is this I have a String array but when I am trying to convert it to an int array I keep getting

java.lang.NumberFormatException

My code is

private void processLine(String[] strings) {
    Integer[] intarray=new Integer[strings.length];
    int i=0;
    for(String str:strings){
        intarray[i]=Integer.parseInt(str);//Exception in this line
        i++;
    }
}

Any help would be great thanks!!!

Answer 1

Suppose, for example, that we have a arrays of strings:

String[] strings = {"1", "2", "3"};

With Lambda Expressions ^{[1] [2]} (since Java 8), you can do the next ▼:

int[] array = Arrays.asList(strings).stream().mapToInt(Integer::parseInt).toArray();

▼ This is another way:

int[] array = Arrays.stream(strings).mapToInt(Integer::parseInt).toArray();

_{—————————
Notes
  1. Lambda Expressions in The Java Tutorials.
  2. Java SE 8: Lambda Quick Start}

Answer 2

To get rid of additional whitespace, you could change the code like this:

intarray[i]=Integer.parseInt(str.trim()); // No more Exception in this line

Answer 3

To help debug, and make your code better, do this:

private void processLine(String[] strings) {
    Integer[] intarray=new Integer[strings.length];
    int i=0;
    for(String str:strings){
        try {
            intarray[i]=Integer.parseInt(str);
            i++;
        } catch (NumberFormatException e) {
            throw new IllegalArgumentException("Not a number: " + str + " at index " + i, e);
        }
    }
}

Also, from a code neatness point, you could reduce the lines by doing this:

for (String str : strings)
    intarray[i++] = Integer.parseInt(str);

Answer 4

Another short way:

int[] myIntArray = Arrays.stream(myStringArray).mapToInt(Integer::parseInt).toArray();

Answer 5

Since you are trying to get an Integer[] array you could use:

Integer[] intarray = Stream.of(strings).mapToInt(Integer::parseInt).boxed().toArray(Integer[]::new);

Your code:

private void processLine(String[] strings) {
    Integer[] intarray = Stream.of(strings).mapToInt(Integer::parseInt).boxed().toArray(Integer[]::new);
}

Note, that this only works for Java 8 and higher.

Answer 6

private void processLine(String[] strings) {
    Integer[] intarray=new Integer[strings.length];
    for(int i=0;i<strings.length;i++) {
        intarray[i]=Integer.parseInt(strings[i]);
    }
    for(Integer temp:intarray) {
        System.out.println("convert int array from String"+temp);
    }
}

Answer 7

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class array_test {

public static void main(String args[]) throws IOException{

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String line = br.readLine();

String[] s_array = line.split(" ");

/* Splitting the array of number separated by space into string array.*/

Integer [] a = new Integer[s_array.length];

/Creating the int array of size equals to string array./

    for(int i =0; i<a.length;i++)
    {
        a[i]= Integer.parseInt(s_array[i]);// Parsing from string to int

        System.out.println(a[i]);
    }

    // your integer array is ready to use.

}

}

Answer 8

This is because your string does not strictly contain the integers in string format. It has alphanumeric chars in it.

Answer 9

public static int[] strArrayToIntArray(String[] a){
    int[] b = new int[a.length];
    for (int i = 0; i < a.length; i++) {
        b[i] = Integer.parseInt(a[i]);
    }

    return b;
}

This is a simple function, that should help you. You can use him like this:

int[] arr = strArrayToIntArray(/*YOUR STR ARRAY*/);