????14??sleep() ?? wait() ????????

????sleep???????Thread????????????′????????????????????л??????????????????????????????????????????????sleep??????????????wait??Object?????????????????wait???????±????????????????????????????????????????????????notify????????notifyAll???????????????????????????????????????????

????15???????????length()????????? String?????length()?????????

???????????length()???????????length???????String????length()?????????

????16??????????String??

????String????final?????????С?

????17??Overload??Override??????Overloaded???????????????????????

????overload????????????????????????????????????????????????Щ????????????????????????????????е???????????????????????????????????β?????????????????????????ɡ???????????????????????????????κ?????????????????????????????????÷?????????????У??????С?

????override??????????????????????????????麯????????壬???????????????????б???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????á?

????18??Set??????????????????????????????????????????? ????==????equals()?? ?????к?????

????Set??Collection??????????????????????????????????????????????null???? equals()???????????????equals()??????==??????? ?????????????????==???????ж??????????????????????????equals???????ж??????????????????????Set??????????????????????á?????java??洢????????set??????????????????????????????????????equals()??????????????????????????????????????equals()???ж??

????19?????????????????runtime exception??

ArithmeticException?? ArrayStoreException?? BufferOverflowException?? BufferUnderflowException?? CannotRedoException?? CannotUndoException?? ClassCastException?? CMMException?? ConcurrentModificationException?? DOMException?? EmptyStackException?? IllegalArgumentException?? IllegalMonitorStateException?? IllegalPathStateException?? IllegalStateException??

ImagingOpException?? IndexOutOfBoundsException?? MissingResourceException?? NegativeArraySizeException?? NoSuchElementException?? NullPointerException?? ProfileDataException?? ProviderException?? RasterFORMatException?? SecurityException?? SystemException?? UndeclaredThrowableException?? UnmodifiableSetException?? UnsupportedOperationException
 

????20??error??exception????????

????Error(????)????????????????????????????java???л????е?????????????????????磬??????????????????????????????????????????????????????????

????Exception(Υ??)??????????????????????д????????????????????????????覴??????????????????????????????????????????????????

????21??abstract class??interface????????

????1> ?????

????A. ?????????????????????????

????B. interface?????abstrct class??????????????????????????????

????2> ?????

????A. interface??????????implements????abstract class?????У????extends??

????B. ?????????????interface?????????????????abstract class??

????C. interface?????????????????abstract class???????????

????D. ????interface?????abstrct class????????????????????????????????????????interface?е???????????????????????????????(declaration?? ??з?????)?????????????????abstract class???????????????????

?????????????????壺

???????Abastract class?в??????е??????????????????Щ????abstract???????????????????????????Щ???abstract?????????Abstrct class?б????巽???塣

????????abstract class????????????????????????????????У?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????

????E. abstract class??interface??Class???н顣

????interface???????????????????????????????????pulic???????????????private??protected?????????????巽???壬???????????????????????interface?????????????????????????JDK?в???????????????????????????????interface??Υ???????????????????????????????????interface??????????????????????????????????????abstract class??Class?С?

????abstract class??interface??Class????????????μ????á?????棬abstract class?????????????????????????淶?????????????????????棬??????????????????壬??????????????????????????????????????????????????????????????á?