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I. Grammar1. Enum is all called enumeration, Chinese is commonly known as enumeration class, learn C + + and other languages of the people, should be to it knows. In the Java language Specification, however, it was introduced in the JDK version 5 and stored in the Java.lang package. In the Java version of the enum is e
()) { System.out.println (e.name ()); System.out.println (E.getdesc ()); } System.out.println (ErrorCodeEnum.SYSTEM_ERROR.name ()); System.out.println (errorcodeenum.valueof (Errorcodeenum.class, "illegal_argument")); String name (): Returns The name of this enum constant, exactly as declared in its enum declaration. Returns the string when the enumerat
The introduction of enum from jdk1.5 is actually a special class, which is easy to write. JVM automatically encapsulates a lot of things for you. Package scjp; The compiled Enum (coffeesize above) also generates a coffeesize. Class Decompilation through class assemblyJavap-C coffeesizeGet the following code: Compiled from "test. java " We can see that each el
;" + day. getDay ()); } WeekDay. printDay (5 ); } } Output result: Mon ===> Monday Tue ===> Tuesday Wed ===> Wednesday Thu ===> Thursday Fri ==> Friday Sat ==> Saturday Sun ==> Sunday Fri 3. Java Enum Principle Although the syntax structure of the Java Enum type is different from that of the
on the values in the enumeration, and the encapsulation is better. InstanceLet's first define a simple enumeration (this is just an example of a simple definition of 3 variables): public enum Sqltypeenum { INSERT, UPDATE, DELETE, SELECT } After parsing the SQL, we get a token, how do we get this token enumeration? This gets: String token = "select"; Sqltypeenum sqltypeenum = sqltypeenum.valueof (Token.touppercase ());
constructing enumeration values. (B) The constructor can only be private. This ensures that external code cannot create new enumeration class instances. 4. All enumeration classes inherit the Enum method. The following describes how to use these methods: (A). ordinal () returns the order in which the enumerated values are declared based on the enumerated values. (B). compareTo () Enum implements the
constructor can only be private, which guarantees that external code cannot build an instance of the enumeration class newly4. All enum classes inherit the methods of the enum, and the following are descriptions of how these methods are used:(a). Ordinal () returns the order of enumeration values in the enumeration type, in the order in which the enumeration values are declared(b). CompareTo ()
Concept enum, called enumeration, is the new feature introduced in JDK 1.5. In Java, enum types that are decorated by keywords are enumerated types. The form is as follows: Enum Color {RED, GREEN, BLUE} If the enumeration does not add any methods, the enumeration value defaults to the ordered value star
sqlTypeEnum = SqlTypeEnum.valueOf(token.toUpperCase()); If not, Java throws an exception:IllegalargumentexceptionNo Enum const class sqltypeenum. xxx I doReason for capital ProcessingThe reason is that the enumeration is in upper case (of course, if your enumeration is in lower case, you will be in lower case, but it is troublesome to mix and write). In fact, valueo
enumeration type to use the enum keyword implies that the type created is a subclass of the Java.lang.Enum class (Java.lang.Enum is an abstract class). The enumeration type conforms to the generic pattern Class enumpublic enum Enumtest {MON, TUE, WED, THU, FRI, SAT, SUN;}This code actually calls the Enum 7 times (String name, int ordinal):New EnumNew EnumNew
CompareTo in the enum returns the difference in the order of the two enumerated values. Of course, the premise is that two enumerated values must belong to the same enumeration class, otherwise the ClassCastException () exception is thrown. (Concrete visible source code)Color.RED.compareTo (Color.Blue); return result-1(3) VALUES () method: A static method that returns an array containing all the enumerated values.Color[] Colors=color.values ();for (C
Recently read the source code of the Hadoop#yarn section. Read to the state machine that part of the time, feel the use of ENMU is too flexible, in the concurrent programming network to translate an article, just met an article. Quickly translate down, rise posture.Original link: http://www.javacodegeeks.com/2011/07/java-secret-using-enum-to-build-state.htmlPeter Lawrey Translator: Chen ZhenyangReviewThe
private, which guarantees that external code cannot build an instance of the enumeration class newly4. All enum classes inherit the methods of the enum, the following are descriptions of the methods used:(a). Ordinal () returns the order of enumeration values in the enumeration type, in the order in which they are declared according to the enumeration values(b). CompareTo ()
Public enum Type {IN ("input parameters "),OUT ("output parameter "),VAR ("variable ");// Define the constructor with parameters so that you can write IN ("....")Private String des;Type (String des){This. des = des;}Public String getDesc (){Return des;}}Public enum State {ON {@ OverrideString getInfo (){Return "open ";}}, OFF {@ OverrideString getInfo (){// TODO Auto-generated method stubReturn null;}};// E
enumeration values. (B) The constructor can only be private. This ensures that external code cannot create new enumeration class instances. 4. All enumeration classes inherit the Enum method. The following describes how to use these methods: (A). ordinal () returns the order in which the enumerated values are declared based on the enumerated values. (B). compareTo () Enum implements the
, and fields to the enumeration type. Of course, the constructor is called only when constructing enumeration constants. A facet is an example:public enum Size{small ("S"), MEDIUM ("M"), LARGE ("L"), Extra_large ("XL");p rivate String abbreviation;private Size ( String abbreviation) {this.abbreviation=abbreviation;} Public String getabbreviation () {return abbreviation;}}All enum types are subclasses of the
Usage One: ConstantsBefore JDK1.5, we defined constants: public static fianl ..... Now, with enumerations, you can group related constants into an enumeration type, and enumerations provide more methods than constants.public enum Color { RED, GREEN, BLANK, YELLOW Usage Two: SwitchThe switch statement before JDK1.6 only supports int,char,enum types, and using enumerations can make our code more readable.
Usage One: ConstantsBefore JDK1.5, we defined constants: public static fianl ..... Now, with enumerations, you can group related constants into an enumeration type, and enumerations provide more methods than constants.public enum Color { RED, GREEN, BLANK, YELLOW Usage Two: SwitchThe switch statement before JDK1.6 only supports int,char,enum types, and using enumerations can make our code more readable.
Usage One: ConstantsBefore JDK1.5, we defined constants: public static fianl ..... Now, with enumerations, you can group related constants into an enumeration type, and enumerations provide more methods than constants.public enum Color { RED, GREEN, BLANK, YELLOW Usage Two: SwitchThe switch statement before JDK1.6 only supports int,char,enum types, and using enumerations can make our code more readable.
Usage One: ConstantsBefore JDK1.5, we defined constants: public static fianl ..... Now, with enumerations, you can group related constants into an enumeration type, and enumerations provide more methods than constants.public enum Color { RED, GREEN, BLANK, YELLOW Usage Two: SwitchThe switch statement before JDK1.6 only supports int,char,enum types, and using enumerations can make our code more readable.
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