I've bean doing some JSP tutorials and I don't understand what the point of a bean class is. All it is, is get and set methods. why do we use them?

Code:
public class UserData {

    String username;
    String email;
    int age;

    public void setUsername( String value )
    {
        username = value;
    }

    public void setEmail( String value )
    {
        email = value;
    }

    public void setAge( int value )
    {
        age = value;
    }

    public String getUsername() { return username; }

    public String getEmail() { return email; }

    public int getAge() { return age; }

}
HTML Code:
<jsp:useBean id="user" class="user.UserData" scope="session"/> 
<HTML>
<BODY>
You entered<BR>
Name: <%= user.getUsername() %><BR>
Email: <%= user.getEmail() %><BR>
Age: <%= user.getAge() %><BR>
</BODY>
</HTML>