In this post, we will look at how to replace the first letter of each word with another letter in Java.

Logic:

• Convert str to char array
• Iterate char array and find the letters whose previous letter is space
• Replace the letter with the new character
• Convert char array back to String

Program

Let’s have a look at the program.

// Java program to demonstrate
// how to replace first character
// of each word with another
// character
public class ReplaceFirstLetter {
        public static void main(String[] args) {

                String str = "java is the best programming language";

                System.out.println("Actual String = " + str);
                // get the char array from str
                char[] charArr = str.toCharArray();
                char newChar = 'P';
                boolean isPreviousCharSpace = true;

                for (int index = 0; index < charArr.length; index++) {

                        // check if the char is a letter
                        if (Character.isLetter(charArr[index])) {

                                // if the previous character
                                // is space then replace the char
                                // with another character
                                if (isPreviousCharSpace) {
                                        // replace char with newChar
                                        charArr[index] = newChar;
                                        // reset the flag
                                        // as we already replaced the char
                                        isPreviousCharSpace = false;
                                }
                        } else {
                                // check if char is space
                                isPreviousCharSpace = true;
                        }
                }

                // print the replaced string
                System.out.println("Replaced String = " + String.valueOf(charArr));
        }
}

Output

Actual String = java is the best programming language
Replaced String = Pava Ps Phe Pest Programming Panguage