如何将字符串的第一个和第四个字符大写？

public class StringManipulation {
    public static String capitalizeFirstAndFourthChar(String str) {
        char[] charArray = str.toCharArray();
        
        if (charArray.length >= 4) {
            charArray[0] = Character.toUpperCase(charArray[0]);
            charArray[3] = Character.toUpperCase(charArray[3]);
        }
        
        return String.valueOf(charArray);
    }
    
    public static void main(String[] args) {
        String input = "example";
        String output = capitalizeFirstAndFourthChar(input);
        System.out.println(output);  // 输出 "exAmple"
    }
}