enumerate:
Before:
the result is normal returns 1. But if introduced to a range of 0-6 is no longer the number,
the compiler what code runs fine, but not what we need him to pass a value that is not restricted. All this time the incoming parameter does not make sense. We define the exe when explicitly accept that int day, but because it is an int, so I can not restrict incoming value, there has been unsafe types of problems.
Use constants to represent the common values on the page:
benefits: a modified everywhere modification, after the success of reduced maintenance, constant in the code tell at a glance, during compilation has been able to confirm the memory space
Question:
1. Type of insecurity: documented column we need to pass a parameter to the date method, the method is int, when you pass arguments do not necessarily have to pass a constant value.
2. No Namespace: Constant naming of high demand, once irregularities. The latter can not understand the significance of the parameters
constant integer used in the case of columns: 3. consistency is poor. In the compiler to complete the memory operation data. In many places we have cited the current value. When you change the list or increase the value listed, all local references need to be recompiled,
This time it was introduced to enumerate :
Enumerated type
What is an enumeration
A method for the enumeration is set to a value contained In a similartype of datain. Enumerated type named will become the enumerationUnparalleledType Description variable to compare with the use of constants, enumerated types can declare the range greater than constant.
For example:
a person's gender: male | female one week only seven days in a month up to 31 days a year for up to 12 months
For objects: 4 seasons a year (Object)
When a variable has a value of several fixed time, or a limited number of objects. You can use an enumeration to represent.
Enumerate the basic use
-Class statement declaring class interfaces -interface statement enumeration -enum
Syntax: Public enum enum {name}
Enumeration members:
Fixed value
at this time, if you need to get Monday, you can order it directly
This time, only to find later Monday to Sunday, another day could not be found.
Enumeration of the benefits brought
Chestnuts:
by enumerating Optimization:
readability greatly improved
Enumeration Features:
1. Any two enumeration values can not have the same name.
Use commas to separate multiple enumeration values 2.
3. If you do not declare enumerated data type display, the system will automatically set the data type int type
The benefits of using enumeration:
1. Use the enumeration class enhances the readability of the code.
2. convey the scope of some constraint values
Advanced: enumerated data types into objects
The object here is not to take over directly to userbean with these objects to be herearrogant, The constructor must be definedprivate(This construction method can only produce one, can not be said to produce a number of enumeration constructor)
this spring when it came out.
"Spring" is not found in printed value previously set
is now just fine.
Summary : In the enumerable object declared objects:
1. The enumeration values must be the first line
2. Declare enumeration object when the constructor must be private. (Purpose: so you can not enumerate this object elsewhere in the statement by designing immutable classes inside his property should be set to the final, which is more secure, and the code is more concise.)
Enumeration method
Each enum class in Java inherits from class java.lang.Enum, when the definition of an enumerated type, each enumeration member can be seen as an instance of Enum class.
Each instance has enumerated the following methods:
代码演示：
values（）方法：以数组的形式返回枚举的所有成员，然后通过foreach方法循环输出。
valurOf():将普通的字符串转换成枚举实例
Oridinal:获取枚举成员索引位置
枚举和接口
同样的，也可以在接口里面使用枚举来组织你的内容。
用法：
枚举同样支持继承抽象类。
Java是单继承模式，只能继承一个类。每个枚举已经继承了java.lang.Enum。但是不妨碍他实现接口、
1.跟普通类一样实现接口，重写抽象方法
2.在接口中使用枚举来组织内容
3.可以在抽象类中，也使用枚举来组织内容EnumMap在枚举类中提供了一个对象EnumMap对象，和hashmap作用是一样，用于存储键值对。数据结构不一样。EnumMap存放的Enum数据类型。底层使用数组来组织内容。在使用这两个对象的时候EnumMap效率更高。
枚举提供的两个特殊的对象：EnumMap、EnumSet
EnumMap是专门为枚举定义map
认识即可，知道是装枚举类型的就行。
如何定义？
EnumSet：是枚举类型的高性能set，要求放入其中的枚举常量必须是同一枚举类型。效率非常高、比hashset效率高。枚举底层元素比较简单，hashset底层比较复杂。
自定义注解：
Servlet in the notes:
the @WebServlet used to configure the servlet, servlet will be loaded when tomcat starts.
@WebFilter This annotation is used to configure filters
What is a comment?
What can solve the problem?
How to learn?
How to optimize?
The basic concept of annotation
comment is very important in the learning process behind the 80 percent are to be developed based on the comments. Spring, hibernate, springmvc frame
annotation is a trend, annotations are only put forward after jdk1.5
Jdk1.5 after the proposed three notes:
@SuppressWarnings: Compression warning
@Deprecated: method definition obsolete
@Override: Rewrite
Annotation: annotation corresponding to a marker, add comments in the program equivalent to the program tagged, the javac, or other types of development tools may be acquired according to the above mechanism based annotation reflected, in accordance with the completion of the corresponding operation function annotation. Tags can be placed classes, attribute parameters and local variables, process, process.
Focus on learning custom annotation:
Notes development process.
Custom annotation
about custom annotation process