I start with an array of strings formatted useful.useless. I need to trim out the .useless part, and then put the useful part in a 2D char array.

I see a way that involves creating a second string array containing only the useful part, and then converting that to a 2D char array, but there is probably a more effective way.

However, I don't know how to convert string array to 2D char array

public static void main (String[]args){
    
    // this here is just to create an array so the example runs
    String in = "useful1.useless1,useful2.useless2,useful3.useless3,";
    String[] strArray = null; 
    strArray = in.split(",");
    
    /*the array of strings is thus
    [useful1.useless1, useful2.useless2, useful3.useless3]
    */
    
    char [][] charArray = new char [strArray.length][];
    
    /* trim from the . so only useful part remains
    then put in 2d char array, which should look like
    
    [u,s,e,f,u,l,1]
    [u,s,e,f,u,l,2]
    [u,s,e,f,u,l,3]
    
    the array will be a ragged array
    */

}

CodePudding user response：

You need to populate charArray at each index, with the array of characters of the desired substring of strArray at the corresponding index. You can do it as shown below:

for (int i = 0; i < strArray.length; i  )
    charArray[i] = strArray[i].substring(0, strArray[i].indexOf('.')).toCharArray();

Demo:

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        // this here is just to create an array so the example runs
        String in = "useful1.useless1,useful2.useless2,useful3.useless3,";
        String[] strArray = in.split(",");

        /*
         * the array of strings is thus [useful1.useless1, useful2.useless2,
         * useful3.useless3]
         */

        char[][] charArray = new char[strArray.length][];
        for (int i = 0; i < strArray.length; i  )
            charArray[i] = strArray[i].substring(0, strArray[i].indexOf('.')).toCharArray();

        // Display
        for (char[] row : charArray)
            System.out.println(Arrays.toString(row));
    }
}

Output:

[u, s, e, f, u, l, 1]
[u, s, e, f, u, l, 2]
[u, s, e, f, u, l, 3]

CodePudding user response：

Stream the strings:

• use regex to “remove” the useless part
• convert the ”useful” String to a char[]
• collect all char[] into a char[][]

Voila:

char[][] usefulChars = Arrays.stream(strArray)
  .map(s -> s.replaceAll("\\..*", ""))
  .map(String::toCharArray)
  .toArray(char[][]::new);

See live demo.