As far as I know, you have to iterate over list items. Try
public static void main(String arg[])
{
List<Character> lc = new ArrayList<Character>();
lc.add('p');
lc.add('r');
lc.add('a');
lc.add('g');
lc.add('y');
lc.add('a');
StringBuilder sb = new StringBuilder();
for (Character c : lc)
sb.append(c.charValue());
String s = sb.toString();
System.out.println(s);
}