java problem

1.An Internet Service Provider (ISP) wants to keep a very large list of unique websites that customers have visited over the course of year 2012. During 2013, as customers visit websites, the ISP would like to be able to very quickly determine whether the site was visited in 2012. What class should they use to hold the 2012 list of websites?

2.A numbered list of kids who are signed up for a soccer league is displayed on a screen. The number of kids is 40-50. The league manager selects kids by number to build teams. For instance, the manager may pick kids 4, 17, 24, to be on a team. What class should be used to hold the kids?

3.An employer stores tax records according to the employees social security number (SSN). The employer must submit these records quarterly to the IRS which requires that they be accessible by SSN and an iterator over the tax records delivers the tax records in order of smallest SSN to largest. What class should be used to store the tax records.