1, there are two types of constructors---instance constructors and static constructors.

2, the static constructor has no parameters.

3, Specification for event: It is defined in class declare,and define correspond method to

it,then to be registered within IMPLEMENTATION. Implement the event: At first ,Instance one

class, Then create object class, register class method not class event.

4, By inheriting : Only the public and protected components of the superclass are visible in

the subclass.

5, Methods that a subclass inherit from a superclass use the private attributes of the

superclass and not any private components of the subclass with the same names.

6, We can use the redefinition addition in the methods statement to redefine an inherited

public or protected instance method in a subclass and make its function more specialized.

when we redefine a method , we cannot change its interface. the method retain the same name

and interface, but has a new implementation.

7, An abatract method is defined in an abatract class and cannot be implemented in that clas.

Instead, it is implemented in a subclass of the class. Abatract classes cannot be

instantiated.

8, A final method cannot be redefined in a subclass. Final classes cannot have subclass.they

conclude an inheritance tree.

9, We cannot redefine the instance constructor of a supercalass in a subclass,neither can we

call one specially using the statement call mehthod constructor.

10, The components of interfaces do not have to be assigned individually to a visibility

section,since they automatically belong to the public section of the class in which the

interface is implementated.

11, Interface do not have an implementation part, since their methods are implemented in the

class that implements the interface.

12, When we use the casting operator, there is no static type check, instead, the system

checks at runtime. ?= .