Java - Write code to replace a string only Once

Requirements

Write code to replace a string only Once

Demo

//package com.book2s;
import java.util.Iterator;

public class Main {
    public static void main(String[] argv) {
        String template = "book2s.com";
        String placeholder = "o";
        String replacement = "O";
        System.out.println(replaceOnce(template, placeholder, replacement));
    }/*  w  w w.j a va  2  s.c o m*/

    public static String replaceOnce(String template, String placeholder,
            String replacement) {
        if (template == null) {
            return template; // returning null!
        }
        int loc = template.indexOf(placeholder);
        if (loc < 0) {
            return template;
        } else {
            return new StringBuffer(template.substring(0, loc))
                    .append(replacement)
                    .append(template.substring(loc + placeholder.length()))
                    .toString();
        }
    }

    public static String toString(Object[] objects) {
        return join(", ", objects);
    }

    public static String join(String seperator, Iterator objects) {
        StringBuffer sb = new StringBuffer();
        if (objects.hasNext())
            sb.append(objects.next());
        while (objects.hasNext()) {
            sb.append(seperator).append(objects.next());
        }
        return sb.toString();
    }

    public static String join(String seperator, Object[] objects) {
        int len = objects.length;
        StringBuffer sb = new StringBuffer(len * 2);
        if (len > 0) {
            sb.append(objects[0]);
            for (int i = 1; i < len; i++) {
                sb.append(seperator).append(objects[i]);
            }
        }
        return sb.toString();
    }
}

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