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Writer：BYSocket（泥沙砖瓦浆木匠）
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When we to set some constants for projects, we always use ‘public static final’to set Int or String constants.Or sometimes,we can also set the paramters in properties.When the project starts,we can get the properties to use them.Today,we can use Enum (JDK 1.5).
Three pieces:
1. An Example to Know Enum
2. How to use EnumSet and EnumMap
3. Enum Analysis
Firstly,we use the Enum to implements Operation.
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package
org.nsg.jdk.testEnum;/** *
@Description OperationTest.java * *
@author BYSocket *
@date 2015-1-8 6:05:59PM *
@version 1.0 */public
class OperationTest{ public
static void main(String[] args) { double
x = 2.0,y=4.0; for
(Operation op : Operation.values()) System.out.printf("%f
%s %f = %f%n", x,op,y,op.apply(x, y)); }}enum
Operation{ PLUS("+") { double
apply(double x,double y){return x + y;} }, MINUS("-") { double
apply(double x,double y){return x - y;} }, TIMES("*") { double
apply(double x,double y){return x * y;} }, DIVIDE("/") { double
apply(double x,double y){return x / y;} }; private
final String symbol; Operation(String
symbol){this.symbol = symbol;} @Override public
String toString(){return symbol;} abstract
double apply(double x,double y);} |
Run as Java application,we can see the Console.The result shows operations
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2.000000
+ 4.000000 = 6.0000002.000000
- 4.000000 = -2.0000002.000000
* 4.000000 = 8.0000002.000000
/ 4.000000 = 0.500000 |
Q:‘The enum is just like class?’
A:Yep,I think that Enum is a nice type.So let us know some methods by apis:
1. Firstly,we can make an abstract method ‘apply()’ ,then set in the constant-specific class body. Its called constant-specific method implementation.
2. We can make constructor with fields to make the enum has vales.(Like String or int …)
3. toString() method : Returns the name of this enum constant, as contained in the declaration. This method may be overridden, though it typically isn’t necessary or desirable. An enum type should override this method when a more programmer-friendly string form exists.
4. ‘vales()’ method :to get all enum objects. And ‘getValue()’ can get the enum object’ value.
Note ‘Its easy to learn how to use.Then learn more and study in depth.’ And in real projects,We can use enums to replace Int or String Enum Pattern.And Enum is also a typesafe enum.
Let us see another example to learn some Sets of Enum.So lets see it:
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package
org.nsg.jdk.testEnum;import
java.util.EnumMap;import
java.util.EnumSet;import
java.util.Iterator;import
java.util.Map.Entry;/** *
@Description WeekTest.java * *
@author BYSocket *
@date 2015-1-9 2:55:10PM *
@version 1.0 */public
class WeekTest{ public
static void main(String[] args) { EnumSet<Week>
weekSet = EnumSet.allOf(Week.class); System.out.println("EnumSet:"); for
(Week w : weekSet) System.out.println(w); EnumMap<Week,
String> weekMap = new EnumMap<Week,
String>(Week.class); weekMap.put(Week.MON,
"星期一"); weekMap.put(Week.TUE,
"星期二"); weekMap.put(Week.WED,
"星期三"); System.out.println("EnumMap:"); for
(Iterator<Entry<Week,
String>> iterator = weekMap.entrySet().iterator(); iterator.hasNext();) { Entry<Week,
String> weekEntry = iterator.next(); System.out.println(weekEntry.getKey().name()+":"+weekEntry.getValue()); } }}enum
Week{ MON("1"),
TUE("2"), WED("3"), THU("4"), FRI("5"), SAT("6"),SUN("7"); private
final String symbol; Week(String
symbol){this.symbol = symbol;} @Override public
String toString(){return symbol;}} |
We can see in Console:
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<font
size="4"
face="宋体">EnumSet:1234567EnumMap:MON:星期一TUE:星期二WED:星期三</font> |
Note： EnumSet or EnumMap is easy for we to use.And with them，we can use enums easily.
We use ‘javap -c -private xxx’to know the class:
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final
class org.nsg.jdk.testEnum.Week extends java.lang.Enum<org.nsg.jdk.testEnum.Week>
{ public
static final org.nsg.jdk.testEnum.Week MON; public
static final org.nsg.jdk.testEnum.Week TUE; public
static final org.nsg.jdk.testEnum.Week WED; public
static final org.nsg.jdk.testEnum.Week THU; public
static final org.nsg.jdk.testEnum.Week FRI; public
static final org.nsg.jdk.testEnum.Week SAT; public
static final org.nsg.jdk.testEnum.Week SUN; private
final java.lang.String symbol; private
static final org.nsg.jdk.testEnum.Week[] $VALUES; public
static org.nsg.jdk.testEnum.Week[] values(); |
We can see ‘Enum is a class.just is a class.’but no extends.
Writer：BYSocket（泥沙砖瓦浆木匠）
微博：BYSocket
豆瓣：BYSocket
Reprint it anywhere u want.
[Java Plasterer] Java Components 3：Java Enum
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原文地址：http://blog.csdn.net/jeffli1993/article/details/42555809
