test

replace(CharSequence target, CharSequence replacement);
replaceAll(String regex, String replacement);
replaceFirst(String regex, String replacement);
System.out.println("abac".replace("a", "\\a")); //\ab\ac
System.out.println("abac".replaceAll("a", "\\\\a")); //\ab\ac
System.out.println("abac".replaceFirst("a", "\\\\a")); //\abac

it seems that we have to escape twice to use 'replaceAll' and 'replaceFirst'.