Replace Each Space with a Character in a String in Java — Definition, Examples and Program

Replace Each Space with a Character in a String in Java

Replacing spaces in a string is a common string manipulation task. It is often used in formatting text, URL encoding, and input normalization.

In this program, we replace every space character (' ') with a given character without using built-in string replacement methods.

How the Logic Works

1. Convert the string into a character array.
2. Traverse each character.
3. If a space is found, replace it with the given character.
4. Reconstruct the string.

Example 1

Input: "Java Programming"

Replace with: '-'

Output: Java-Programming

Example 2

Input: "Hello World Java"

Replace with: '*'

Output: Hello*World*Java

Java Program to Replace Each Space with a Character

import java.util.Scanner;

public class ReplaceSpace {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        System.out.print("Enter a string: ");
        String str = sc.nextLine();

        System.out.print("Enter replacement character: ");
        char replaceChar = sc.next().charAt(0);

        char[] chars = str.toCharArray();

        for (int i = 0; i < chars.length; i++) {
            if (chars[i] == ' ') {
                chars[i] = replaceChar;
            }
        }

        System.out.println("Modified String: " + new String(chars));
    }
}

Sample Output

Enter a string: Practice makes perfect
Enter replacement character: _
Modified String: Practice_makes_perfect

Important Notes

• No replace() or replaceAll() method is used.
• Only space characters are replaced.
• Time complexity is O(n).

Practice Challenges

1. Replace spaces with multiple characters like "%20".
2. Replace only the first occurrence of space.
3. Count how many spaces were replaced.

This problem helps in understanding character-level manipulation and safe string transformations in Java.