The famous Y2K bug occurred because some old programs used two decimal digits to store years. This became a problem in the year 2000, because such programs had no way to tell whether "00" meant 1900 or 2000.

A similar problem will occur for Java programs when the number of milliseconds since the beginning of 1970 exceeds the capacity of a long. In what year will this occur, given that the maximum value of a long is 9,223,372,036,854,775,807? What if getTime() returned an int, which has a maximum value of 2,147,483,647? What about those UNIX/C systems which use an int to store the number of seconds since the beginning of 1970?