BitSet: bit set to achieve a common logical operation.
Calendar: Date of many obsolete methods in such a reality. It is an abstract class, there are two implementations were GregorianCalendar and JapaneseImperialCalendar
Formatter: String.format () method is in fact built a Formatter to format the new operation, to provide the print format similar to C language output.
Locale: Locale to perform its task is called locale-sensitive operation of the operation.
Observer Interface and Observable Class : JDK provides the framework to achieve observer pattern, under this framework: Observer Object should implement the Observer interface (only update method), by observers as a subclass of Observable, Observable can add / remove any more than between one Observer,
When the call is actually called when notifyObservers held Observable Observer's update method. This framework is not easy to use, with the inherited way limit the scope of its application.
Properties: A very popular class, but few know that it is inherited from the HashTable, this design is not good, because you can even call the parent class, add method to join non-String's Key, are damned to please a bad inheritance better design should be allowed to hold HashTable Properties class reference, with the combination of problem-solving.
Here is a misuse of inheritance examples of live fresh fresh!!! GetProperty not add synchronized, and setProperty added synchronized keyword.
RandomAccess: with this interface can support the tag of the form get (i) fast access, in general, Array implementation support fast access, while maintaining Linked to achieve because only a headNode perhaps sub tailNode, and get (i) when it was down Zhaoyazhaoya node from scratch, of course, low efficiency of friends. Has been tested in the ArrayList's iterator () compared to direct for () (get (i))
Slightly more slowly (but bring the benefits of unified interface), while LinkedList of iterator () than for () (get (i)) on the number of higher efficiency.
Random: This class is a mechanism to change the default seed, the original is the current time in milliseconds as a seed, so if the CPU fast enough in the same loop may be taken out of the same seed. Ms now become a nanosecond, but also with static variables from the increase, in theory, it is impossible for the seeds of the same.
Scanner: One can use regular expressions to parse primitive types and strings of simple text scanner, combined with System.in to use it very good.
TimeZone: Time zone-related, a default implementation is SimpleTimeZone.
Timer: Timer can execute a fixed time or delay the implementation of the (TimeTask implemtns Runalbe), you can periodically the implementation of the thread (TimeTask). In fact, Timer which maintained TaseQueue, the Queue the next execution time by task order (small top of the heap), the implementation of a TimeTask will complete the implementation according to the time the next appropriate wait (fixTime) rather than the air circulation, thus improving efficiency .
UUID: using the time machine with the card or some other parameters to make the hash, basically to ensure uniqueness.