1) instanceof: The object of a class that implements a certain interface is also an instance of the interface; the object of a certain class is also an instance of the super class of the class.
2) The method modified by native() has no method body, and a semicolon ";" is used instead of braces.
3)main is not a keyword.
4) System.exit(int value), that is to say, as long as it is int, the JVM can exit System.exit('a'); the same is legal.
5)&,| can be used on int and boolean, but ^ (XOR) can only be used on int.
6) If a class and an interface are defined in the same file, and the class is declared as public, nothing can be written before the interface, because the interface can only be modified with public, and there can only be one public access in a file Control keywords.
7) unreachable statement Unreachable statement will appear in the following situations:
(1) Write the statement after the reutrn statement.
(2) Write the statement after the throw statement.
(3) Define statements after break and continue statements.
8) "/u10100" // legal, equivalent to '/u1010' and the string "0"
9) The shift operator can be used for long int char short byte
10) The access control character of a class can be public or add nothing.
11) goto is a reserved word but not a keyword. then is nothing.
12) When the type of the super class is forced to be assigned to the object of the sub class, there will be no exception in compilation, but an exception will occur during runtime.