StringBuffer provides several versions of the append() method to convert and append other objects and primitive data types to StringBuffer objects. : StringBuffer « Utility Classes « SCJP

1. SCJP
2. Utility Classes
3. StringBuffer

public class MainClass {
 public static void main(String args[]) {
  StringBuffer sb = new StringBuffer(" is ");
  sb.append("A");
  sb.append('!');
  sb.insert(0,"Java");
  sb.append('\n');
  sb.append("This is ");
  sb.append(true);
  sb.setCharAt(21,'T');
  sb.append('\n');
  sb.append("Java");
  sb.append(1);
  String s = sb.toString();
  System.out.println(s);
 }
}

Java is A!
This is trTe
Java1