String[] userid = {"aa","bb","cc"};
List<String> userList = new ArrayList<String>();
Collections.addAll(userList, userid);

String[] userid = {"aa","bb","cc"};
List<String> userList = Arrays.asList(userid);

List list = new ArrayList(Arrays.asList(userid));

String[] userid = {"aa","bb","cc"};
List<String> userList = new ArrayList<String>(userid.length);
for(String uid: userid){
userList.add(uid);
}

List<String> strList = new ArrayList<String>();
strList.add("aa");
strList.add("bb");
Object[] objs = strList.toArray();

String[] strs = (String[]) strList.toArray();

final int size = strList.size();
String[] strs = (String[])strList.toArray(new String[size]);

List<String> strList = new ArrayList<String>();
strList.add("aa");
strList.add("bb");
String[] strs = new String[strList.size()];