[JAVA] Uppercase only the specified range with substring. (How to use substring)

/*
substring extracts characters.
The argument contains the index of the character.
* Index starts from 0
*/

/*
When there are two arguments
Example:
String str = "012345";
substring(Starting position,End position);
substring(0, 3)
The extracted characters are[012]
* The end position is 3, but it is not included in the extracted characters.

If there is one argument, it is the start position.
Example:
String str = "012345";
substring(Starting position);
substring(3);
The extracted characters are[345]
*/

/*
* Blanks are included in the index
String str = "0 12345";(Half-width blank)
substring(Starting position);
substring(3);
The extracted characters are[2345]become
*/

import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        
        int a = sc.nextInt();
        int b = sc.nextInt();
        sc.nextLine();
        String str = sc.nextLine();
        
        System.out.println(str.substring(0, a - 1) + str.substring(a - 1, b).toUpperCase() + str.substring(b));
    }
}

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