????????Java??????????null????????????????????????????????NPE??????????Java????????????????????????????Java????????null???null????????????????????????Java?????????null??????????????????????????鷳??????null????????Java??
??????????е????棬???java?????????????????飬???????????????????????????????????????????null?????????????e??????????????????????????????????null??Java???????????????????????????????null?????????????null?????е????????????????????null???????????null??
?????????Java???????null???????????null?????Java?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????Java??null??????????????????е????????null???????????????Щ???????????????????????Щ????null?????μ????????????????????Java??null???Щ??????ɡ?
????Java?е?Null??????
?????????????????????null??Java??????????????null??????????????Щ??????????????????????????????????????????????????????????????Java???????????????????????????У??????????Java??null?????????????????????Щ????????????????null?????????α???????????????
????1???????null??Java?е????????public??static??final???????Сд??е???????nullд??Null??NULL???????????????????????????
????Object obj = NULL; // Not Ok
????Object obj1 = null  //Ok
??????????????????????????????????????????IDE??????????????????????????????????????????????IDE??Eclipse??Netbeans???????????????????????????????notepad??Vim??Emacs????????????????????????
????2???????????????????????????int?????0??boolean???????false??null???κ?????????????????????????????object????????????????????????????????????????false??????????????Java?е??κ????????????null???????????????б????????????????????????????????????????????????????????????????г??????????????????????????????????????????????????????????????????????????????????????????????????????
????private static Object myObj;
????public static void main(String args[]){
????System.out.println("What is value of myObjc : " + myObj);
????}
????What is value of myObjc : null
????????????????object????????????????????????????????????myObj???????????????????????????????????????????????????????????????????÷?????????
????3????????????Щ???null?????????????????????????????????????????????丳???κ??????????????????null??????κ??????????????????
????String str = null; // null can be assigned to String
????Integer itr = null; // you can assign null to Integer also
????Double dbl = null;  // null can also be assigned to Double
????String myStr = (String) null; // null can be type cast to String
????Integer myItr = (Integer) null; // it can also be type casted to Integer
????Double myDbl = (Double) null; // yes it's possible?? no error
????????????????????????????null?????????κ??????????????е????????????????????????????
????4??null??????????????????????null?????????????????????int??double??float??boolean??????????????????????????????????????
????int i = null; // type mismatch : cannot convert from null to int
????short s = null; //  type mismatch : cannot convert from null to short
????byte b = null: // type mismatch : cannot convert from null to byte
????double d = null; //type mismatch : cannot convert from null to double
????Integer itr = null; // this is ok
????int j = itr; // this is also ok?? but NullPointerException at runtime
????????????????????????????null??????????????????????????????????null??????????object?????object???????????????????????????????????????????????????????????????Java?е?????????μ???????????????????????