problem in <s:select> usage

Hi,
I am trying to use the following code in Action class & JSP in struts2.
But I get the error message saying "tag 'select', field 'list', name 'country': The requested list key 'countryList' could not be resolved as a collection/array/map/enumeration/iterator type"

Code in Action class

package com.infosys;
import java.util.ArrayList;
import com.opensymphony.xwork2.ActionSupport;

public class RegisterAction extends ActionSupport 
{
                private String userName;
	private String password;
	private String gender;
	private String about;
	private String country;
	private ArrayList<Country> countryList;
	private String[] community;
	private ArrayList<String> communityList;
	private Boolean  mailingList;
	
                public RegisterAction()
	{
		countryList = new ArrayList<Country>();
		communityList = new ArrayList<String>();
		community = new String[]{"Java",".Net"};
	}
	public String populate() 
	{
		countryList.add(new Country(1, "India"));
		countryList.add(new Country(2, "USA"));
		countryList.add(new Country(3, "France"));
		
		communityList.add("Java");
		communityList.add(".Net");
		communityList.add("SOA");
		
		mailingList = true;
		return "populate";
	}
	public String execute() 
               {
		return SUCCESS;
	}
  
	public String getUserName() {
		return userName;
	}

public void setUserName(String userName) {
		this.userName = userName;
	}

public String getPassword() {
		return password;
	}

public void setPassword(String password) {
		this.password = password;
	}

public String getGender() {
		return gender;
	}

public void setGender(String gender) {
		this.gender = gender;
	}

public String getAbout() {
		return about;
	}

public void setAbout(String about) {
		this.about = about;
	}

public String getCountry() {
		return country;
	}

public void setCountry(String country) {
		this.country = country;
	}

public ArrayList<Country> getCountryList() {
		return countryList;
	}

public void setCountryList(ArrayList<Country> countryList) {
		this.countryList = countryList;
	}

public String[] getCommunity() {
		return community;
	}

public void setCommunity(String[] community) {
		this.community = community;
	}

public ArrayList<String> getCommunityList() {
		return communityList;
	}

public void setCommunityList(ArrayList<String> communityList) {
		this.communityList = communityList;
	}

public Boolean getMailingList() {
		return mailingList;
	}

public void setMailingList(Boolean mailingList) {
		this.mailingList = mailingList;
	}

}

code in jsp

Please let me know the reason for error & how to go about in solving the problem.

Thanks

apparently you are not instantiating your action class which creates ArrayList and field variable for jsp,
for that you can make your index.jsp or your 1st page that loads on running project look like this

then in your struts.xml

and finally you need to populate your Country list
add simple populate(); line in your execute method which will populate your List or you can use Preparable interface