Hello Everybody!
First, I'm really sorry but my English is not so good.
Well, I have two classes, User.java and ArrayListDemo.java, when I compile the second class (after compile the first class perfectly)I get this warning:

warning: [unchecked] unchecked call to add(E) as a member of the raw type java.util.ArrayList
    userlist.add(usr3);
                /

What's the problem? Why can't I add my object usr3?
Can Anyone help me? Thanks!!!

User.java
package com.wrox.utilities;


public class User {

       private String username;
       private String phonenumber;

       public String getUsername() {
              return username;
       }

       public void setUsername(String uname) {
              this.username = uname;
       }

       public String getPhonenumber() {
              return phonenumber;
       }

       public void setPhonenumber(String pnumber) {
              this.phonenumber = pnumber;
       }

       public User(){
       }

       public User(String uname, String pnumber){
              this.username = uname;
              this.phonenumber = pnumber;
       }



}



ArrayListDemo.java
package com.wrox.utilities;
import java.util.ArrayList;

public class ArrayListDemo {
       /* método estatico MAIN */

       public static void main(String[] args) {

         User usr1 = new User("J Smith", "123-444-4444");
         User usr2 = new User("M Walker", "123-555-5555");
         User usr3 = new User("R Johnson", "123-666-6666");

         ArrayList userlist = new ArrayList();
         userlist.add(usr3);

         System.out.println("USERS LIST:");

         for (int i=0; i<userlist.size(); i++){
            User usr = (User) userlist.get(i);
            System.out.println("User name: " + usr.getUsername());
            System.out.println("Phone Number: " + usr.getPhonenumber());
         }


       }



}