如何使用Java从字符串中获取单个字符？

public class Main {
    public static void main(String[] args) {
        String str = "Hello, World!";
        char firstChar = str.charAt(0);
        char secondChar = str.charAt(1);
        System.out.println("First character: " + firstChar);
        System.out.println("Second character: " + secondChar);
    }
}

First character: H
Second character: e

public class Main {
    public static void main(String[] args) {
        String str = "Hello, World!";
        for (int i = 0; i < str.length(); i++) {
            char ch = str.charAt(i);
            System.out.println("Character at index " + i + ": " + ch);
        }
    }
}

Character at index 0: H
Character at index 1: e
Character at index 2: l
Character at index 3: l
Character at index 4: o
Character at index 5: ,
Character at index 6:  
Character at index 7: W
Character at index 8: o
Character at index 9: r
Character at index 10: l
Character at index 11: d
Character at index 12: !

public class Main {
    public static void main(String[] args) {
        String str = "Hello, World!";
        char[] charArray = str.toCharArray();
        for (int i = 0; i< charArray.length; i++) {
            char ch = charArray[i];
            System.out.println("Character at index " + i + ": " + ch);
        }
    }
}

Character at index 0: H
Character at index 1: e
Character at index 2: l
Character at index 3: l
Character at index 4: o
Character at index 5: ,
Character at index 6:  
Character at index 7: W
Character at index 8: o
Character at index 9: r
Character at index 10: l
Character at index 11: d
Character at index 12: !