Replace blanks in a string with "%20"

ReplaceBlank.java

package kata.string;

public class ReplaceBlank {
    /**
     * if you can use the String Buffer
     */
    public String replaceBlankWithStringBuilder(String input) {

        StringBuilder sb = new StringBuilder();

        for (int i = 0; i < input.length(); i++) {
            if (input.charAt(i) == ' ') {
                sb.append("%20");
            }
            else {
                sb.append(input.charAt(i));
            }
        }

        return sb.toString();
    }

    public String replaceBlank(String inputStr) {
        char[] output = null;
        int numberOfBlanks = 0;

        // find total number of blank space in the input string
        for (int i = 0; i < inputStr.length(); i++) {
            char ch = inputStr.charAt(i);
            if (ch == ' ') {
                numberOfBlanks++;
            }
        }

        // create the output buffer
        output = new char[inputStr.length() + 2 * numberOfBlanks];

        // copy into the output array from the end
        int inputEndPointer = inputStr.length()-1, outputEndPointer = output.length-1;
        while (inputEndPointer >= 0) {
            char ch = inputStr.charAt(inputEndPointer);
            if (ch == ' ') {
                output[outputEndPointer--] = '0';
                output[outputEndPointer--] = '2';
                output[outputEndPointer--] = '%';
            }
            else {
                output[outputEndPointer--] = ch;
            }
            inputEndPointer--;
        }

        return new String(output);
    }
}