Foo.java

import java.util.ArrayList;
import java.util.List;
import java.lang.StringBuffer;

public class Foo {
  public static void main(String[] args) {
    List<StringBuffer> list = new ArrayList<StringBuffer>();
    list.add(new StringBuffer("foo"));
    System.out.println(list.get(0));
    list.get(0).append("bar");
    System.out.println(list.get(0));
  }

}