Suppose the CashRegister needs to support a method void undo() that undoes the addition of the preceding item. This enables a cashier to quickly undo a mistake. What instance variables should you add to the CashRegister class to support this modification

previousAddition instance variable

Explanation:

In order to accomplish this you would need to add a previousAddition instance variable. In this variable you would need to save the amount that was added at the end of the process. Therefore, if a mistake were to occur you can simply call the previousAddition variable which would have that amount and subtract it from the total. This would quickly reverse the mistake, and can be easily called from the undo() method.

a  social news website  is an  internet  website  that features  user-posted stories. such stories are ranked based on popularity, as voted on by other users of the site or by website administrators. users typically comment online on the news posts and these comments may also be ranked in popularity. since their emergence with the birth of  web 2.0, social news sites have been used to link many types of information, including news, humor, support, and discussion. all such websites allow the users to submit content and each site differs in how the content is moderated. on the  slashdot  and  fark  websites,  administrators  decide which articles are selected for the front page. on  reddit  and  digg, the articles that get the most votes from the community of users will make it to the front page. many social news websites also feature an online comment system, where users discuss the issues raised in an article. some of these sites have also applied their voting system to the comments, so that the most popular comments are displayed first. some social news websites also have a  social networking  function, in that users can set up a user profile and follow other users' online activity on the website.