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This article mainly explains "what is the function of enumeration in Java". The content in the article is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "what is the function of enumeration in Java".

First, the derivation of enumerations

Set a scenario, the business requires one of our inputs to have several states, how to express these states? Most of them may directly use static final to represent a variable of type int. As follows:

/ / order status public static final int ORDER_DEPOT_UNPAY = 0; public static final int ORDER_DEPOT_PAID = 1; public static final int ORDER_DEPOT_TIMOUT = 2

Then the next business logic is to use these constant values to refer to various basic business meanings. But the disadvantages are as follows.

1. It's just data of type int. What if we define another variable and the number is the same as him? such as

Public static final int ORDER_LOGISTICS_READY = 0; public static final int ORDER_LOGISTICS_TRANSPORT = 1; public static final int ORDER_LOGISTICS_ARRIVED = 2

What if I want to use one of the above three states and the wrong input weighs the following type? Because in the business implementation, they finally show the same number, which is the same as TM.

two。 These variables we are just a number, after getting the number, what if I want to know the specific meaning? You also need to construct a mapping table of numbers and meanings.

3. These constants are of static final type. If such constants are used in some places when the class is loaded, the indirect reference to the class load will directly program the constant reference!

It is better to use enumeration at this time.

Public enum Depot {UNPAY, PAID, TIMOUT} / / 0,1,2 public enum Logistics {READY, TRANSPORT, ARRIVED} / / 0,1,2

Then, if you need a value, you can call it this way (the enumerated class will automatically number the instance starting from 0 by default)

Public static void main (String [] args) {System.out.println (Depot.UNPAY); System.out.println (Depot.UNPAY.ordinal ());} II, enumerate advanced levels

But what if we change their specific serial numbers at this time? such as

/ / order status public static final int ORDER_DEPOT_UNPAY = 0; public static final int ORDER_DEPOT_PAID = 3; / / value changed public static final int ORDER_DEPOT_TIMOUT = 2

We can enrich an enumerated class by knowing that the type in the enumerated class must be several instances of that class. The rest of the operations are no different from class and object operations. Demo is as follows

Public enum DepotEnum {UNPAY (0, "unpaid"), PAID (1, "paid"), TIMOUT (- 1, "timeout"); private int status; / / status private String desc; / / meaning description private String dbInfo;// other attributes private DepotEnum (int status, String desc) {this.status = status; this.desc = desc;} public int getStatus () {return status } public String getDesc () {return desc;} public String getDbInfo () {return dbInfo;} public int calcStatus (int params) {return status + params;} public static void main (String [] args) {for (DepotEnum e: DepotEnum.values ()) {System.out.println (e + ":" + e.calcStatus (14)) } three, move on

What if some of our states are bound to some rows in the enumeration? JDM provides enumerated types that can also be used in switch, such as our addition, subtraction, multiplication and division. We can implement this switch function in it.

Public class ActiveEnum {public enum NormalActive {PLUS,MINUS,MULTI,DIVIDS; double oper (double xmerie double y) {switch (this) {case PLUS:return xray; case MINUS:return Xmury Case MULTI:return xtriple; case DIVIDS:return xramy;} throw new UnsupportedOperationException () / / the meaning of this existence is only to replace default}} public static void main (String [] args) {System.out.println (NormalActive.PLUS.oper (0.1,0.2));}}

There may be times when we need to add new features, such as adding a new DIFFER function, whether I want to add enumerated types, add switch statements.

At this point, we can optimize the code again (always keep in mind that enumerated types are class-to-instance).

Public class ActiveEnum {public enum BetterActive {PLUS {@ Override double oper (double x, double y) {return xroomy }}, MINUS {@ Override double oper (double XJI double y) {return XMY;}}; abstract double oper (double XJI double y) / / introduction of abstract class} public static void main (String [] args) {System.out.println (NormalActive.PLUS.oper (0.1,0.2));}} IV, policy enumeration introduces

For example, we now have to calculate the overtime pay for employees, and the rule is to calculate twice the overtime pay on weekdays and three times the overtime pay on holidays.

/ * * @ author sowhat * description: overtime pay: 2 times overtime on weekdays and 3 times on holidays * / enum PayDay {MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY; private static final int HOURS_WORK = 2; private static final int HOURS_REST = 3 / / timeout double pay (double hoursOvertime) {switch (this) {case SATURDAY:case SUNDAY: return hoursOvertime*HOURS_REST; default: return hoursOvertime*HOURS_WORK;}

But what if I want to add a 51 holiday at this time? We can consider introducing policy enumerations. Then wrap the policy enumeration with an external enumeration.

Public enum BetterPayDay {MONDAY (PayType.WORK), TUESDAY (PayType.WORK), WEDNESDAY (PayType.WORK), THURSDAY (PayType.WORK), FRIDAY (PayType.WORK), SATURDAY (PayType.REST), SUNDAY (PayType.REST), WUYI (PayType.REST); private final PayType payType; / / member variable then defines an external enumeration to wrap the policy enumeration. BetterPayDay (PayType payType) {this.payType = payType;} double pay (double hoursOvertime) {return payType.pay (hoursOvertime);} / Policy enumeration We only define the salary calculation method for working days or holidays. Private enum PayType {WORK {double pay (double hoursOvertime) {return hoursOvertime*HOURS_WORK }}, REST {double pay (double hoursOvertime) {return hoursOvertime*HOURS_REST;}}; private static final int HOURS_WORK = 2 Private static final int HOURS_REST = 3; abstract double pay (double hoursOvertime); / / Abstract method for calculating overtime pay} public static void main (String [] args) {System.out.println (BetterPayDay.MONDAY.pay (7.5)) }} Thank you for your reading, the above is the content of "what is the function of enumeration in Java". After the study of this article, I believe you have a deeper understanding of what the function of enumeration in Java is, and the specific use needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

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