ActionFormクラスが継承できないのですが・・・

package gourmet;
import org.apache.struts.action.*;

public final class PostMessageForm extends ActionForm{
	private String shopName;
	private String criticName;
	private String messageBody;

	public void setShopName(String shopName){
			this.shopName=shopName;
			}
	public String getShopName(){
			return shopName;
			}
	public void setCriticName(String criticName){
			this.criticName = criticName;
			}
	public String getCriticName(){
			return criticName;
			}
	public void setMessageBody(String messageBody){
			this.messageBody = messageBody;
			}
	public String getMessageBody(){
			return messageBody;
			}