public class Main {
public static void main(String args[]) throws Exception {
String str = "this is a test";
System.out.println(replaceCharAt(str, 0, 'd'));
}
public static String replaceCharAt(String s, int pos, char c) {
StringBuffer buf = new StringBuffer(s);
buf.setCharAt(pos, c);
return buf.toString();
}
}
//dhis is a test