blocks|key|3105370|text|将其更改为：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3105371|switch+(enumExample)+{
++++case+VALUE_A:+{
++++++++//..
++++++++break;
++++}
}|code-block|syntax|javascript|3105372|线索在错误中。您不需要使用枚举类型来限定case标签，只需要限定它的值。|offset|length|style|CODE|3105373|entityMap^0|0|0|K|4|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Change it to this:

<pre><code>switch (enumExample) {
 case VALUE_A: {
 //..
 break;
 }
}
</code></pre>

The clue is in the error. You don't need to qualify <code>case</code> labels with the enum type, just its value.

blocks|key|228667|text|Java会自动推断case中元素的类型，所以标签一定是不合格的。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|228668|int+i;
switch(i)+{
+++case+5:+//+<-+integer+is+expected
}
MyEnum+e;
switch+(e)+{
+++case+VALUE_A:+//+<-+an+element+of+the+enumeration+is+expected
}|code-block|syntax|javascript|228669|entityMap^0|9|4|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

Java infers automatically the type of the elements in <code>case</code>, so the labels must be unqualified.

<pre><code>int i;
switch(i) {
 case 5: // &lt;- integer is expected
}
MyEnum e;
switch (e) {
 case VALUE_A: // &lt;- an element of the enumeration is expected
}
</code></pre>

blocks|key|232565|text|错误：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|232566|case+AnotherClass.MyEnum.VALUE_A|code-block|syntax|javascript|232567|右图：|232568|case+VALUE_A:|232569|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Wrong: 

<pre><code>case AnotherClass.MyEnum.VALUE_A
</code></pre>

Right:

<pre><code>case VALUE_A:
</code></pre>

blocks|key|232561|text|这应该可以做到：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|232562|//Main+Class
public+class+SomeClass+{

++++//Sub-Class
++++public+static+class+AnotherClass+{
++++++++public+enum+MyEnum+{
++++++++++++VALUE_A,+VALUE_B
++++++++}++++
++++++++public+MyEnum+myEnum;
++++}

++++public+void+someMethod()+{+
++++++++AnotherClass.MyEnum+enumExample+=+AnotherClass.MyEnum.VALUE_A;+//...

++++++++switch+(enumExample)+{
++++++++++++case+VALUE_A:+{+//<--+error+on+this+line
++++++++++++//..
++++++++++++break;
++++++++++++}
++++++++}
++++}
}|code-block|syntax|javascript|232563|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

this should do:

<pre><code>//Main Class
public class SomeClass {

 //Sub-Class
 public static class AnotherClass {
 public enum MyEnum {
 VALUE_A, VALUE_B
 } 
 public MyEnum myEnum;
 }

 public void someMethod() { 
 AnotherClass.MyEnum enumExample = AnotherClass.MyEnum.VALUE_A; //...

 switch (enumExample) {
 case VALUE_A: { //&lt;-- error on this line
 //..
 break;
 }
 }
 }
}
</code></pre>

blocks|key|228675|text|这就是我使用它的方式。它工作得很棒-|type|unstyled|depth|inlineStyleRanges|entityRanges|data|228676|public+enum+Button+{
++++++++REPORT_ISSUES(0),
++++++++CANCEL_ORDER(1),
++++++++RETURN_ORDER(2);

++++++++private+int+value;

++++++++Button(int+value)+{
++++++++++++this.value+=+value;
++++++++}

++++++++public+int+getValue()+{
++++++++++++return+value;
++++++++}
++++}|code-block|syntax|javascript|228677|和如下所示的switch-case|offset|length|style|CODE|228678|@Override
public+void+onClick(MyOrderDetailDelgate.Button+button,+int+position)+{
++++switch+(button)+{
++++++++case+REPORT_ISSUES:+{
++++++++++++break;
++++++++}
++++++++case+CANCEL_ORDER:+{
++++++++++++break;
++++++++}
++++++++case+RETURN_ORDER:+{
++++++++++++break;
++++++++}
++++}
}|228679|entityMap^0|0|0|6|B|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

This is how I am using it. And it is working fantastically -

<pre><code>public enum Button {
 REPORT_ISSUES(0),
 CANCEL_ORDER(1),
 RETURN_ORDER(2);

 private int value;

 Button(int value) {
 this.value = value;
 }

 public int getValue() {
 return value;
 }
 }
</code></pre>

And the <code>switch-case</code> as shown below

<pre><code>@Override
public void onClick(MyOrderDetailDelgate.Button button, int position) {
 switch (button) {
 case REPORT_ISSUES: {
 break;
 }
 case CANCEL_ORDER: {
 break;
 }
 case RETURN_ORDER: {
 break;
 }
 }
}
</code></pre>

blocks|key|2891408|text|从Java14开始，可以使用切换表达式。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|2891409|对于这篇文章|2891410|public+enum+MyEnum+{
++++VALUE_A,+VALUE_B;
}|code-block|syntax|javascript|2891411|public+void+someMethod()+{+
++++MyEnum+enumExample+//...

++++switch+(enumExample)+{
++++++++case+VALUE_A+->+{
++++++++++++//+logic
++++++++}
++++++++case+VALUE_B+->+{
++++++++++++//+logic
++++++++}+++
++++}
}|2891412|切换表达式|2891413|与所有表达式一样，|2891414|开关表达式的计算结果为单个值，并且可以在语句中使用。它们可能包含"case+L+->“标签，以消除对break语句的需要，以防止失败。您可以使用yield语句指定switch表达式的值。|blockquote|2891415|2891416|2891417|public+enum+Month+{
++++JAN,+FEB,+MAR,+APR,+MAY,+JUN,+JUL,+AUG,+SEP,+OCT,+NOV,+DEC;
}|2891418|示例1:返回值。|2891419|public+static+int+getNoOfDaysInAMonth(Month+month,+boolean+isLeapYear)+{
++++return+switch(month)+{
++++++++case+APR,+JUN,+SEP,+NOV+->+30;
++++++++case+FEB+->+(isLeapYear)?+29:+28;
++++++++case+JAN,+MAR,+MAY,+JUL,+AUG,+OCT,+DEC+->+31;
++++};
}|2891420|示例2:不返回值。|2891421|public+static+void+printNoOfDaysInAMonth(Month+month,+boolean+isLeapYear)+{
++++switch(month)+{
++++++++case+APR,+JUN,+SEP,+NOV+->+{
++++++++++++System.out.println("30+days");
++++++++}
++++++++case+FEB+->+{
++++++++++++System.out.println(((isLeapYear)?+29:+28)+%2B+"+days");
++++++++}
++++++++case+JAN,+MAR,+MAY,+JUL,+AUG,+OCT,+DEC+->+{
++++++++++++System.out.println("31+days");
++++++++}
++++};
}|2891422|参考文献|2891423|Switch+Expressions|2891424|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.oracle.com/en/java/javase/15/language/switch-expressions.html^0|1|6|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0|I|0|0^^$0|@$1|2|3|4|5|6|7|1J|8|@$9|1K|A|1L|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1M|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1N|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|J|7|1O|8|@]|D|@]|E|$K|L]]|$1|O|3|P|5|6|7|1P|8|@]|D|@]|E|$]]|$1|Q|3|R|5|6|7|1Q|8|@]|D|@]|E|$]]|$1|S|3|T|5|U|7|1R|8|@]|D|@]|E|$]]|$1|V|3|-4|5|6|7|1S|8|@]|D|@]|E|$]]|$1|W|3|-4|5|6|7|1T|8|@]|D|@]|E|$]]|$1|X|3|Y|5|J|7|1U|8|@]|D|@]|E|$K|L]]|$1|Z|3|10|5|6|7|1V|8|@]|D|@]|E|$]]|$1|11|3|12|5|J|7|1W|8|@]|D|@]|E|$K|L]]|$1|13|3|14|5|6|7|1X|8|@]|D|@]|E|$]]|$1|15|3|16|5|J|7|1Y|8|@]|D|@]|E|$K|L]]|$1|17|3|18|5|6|7|1Z|8|@]|D|@]|E|$]]|$1|19|3|1A|5|6|7|20|8|@]|D|@$9|21|A|22|1|23]]|E|$]]|$1|1B|3|-4|5|6|7|24|8|@]|D|@]|E|$]]]|1C|$1D|$5|1E|1F|1G|E|$1H|1I]]]]

From Java 14 onwards, one can use switch expressions.
For this post
<pre><code>public enum MyEnum {
 VALUE_A, VALUE_B;
}
</code></pre>
<pre><code>public void someMethod() { 
 MyEnum enumExample //...

 switch (enumExample) {
 case VALUE_A -&gt; {
 // logic
 }
 case VALUE_B -&gt; {
 // logic
 } 
 }
}
</code></pre>
Switch expression
<blockquote>
Like all expressions, switch expressions evaluate to a single value and can be used in statements. They may contain &quot;case L -&gt;&quot; labels that eliminate the need for break statements to prevent fall through. You can use a yield statement to specify the value of a switch expression.
</blockquote>
<pre><code>public enum Month {
 JAN, FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT, NOV, DEC;
}
</code></pre>
Example 1: Returns value.
<pre><code>public static int getNoOfDaysInAMonth(Month month, boolean isLeapYear) {
 return switch(month) {
 case APR, JUN, SEP, NOV -&gt; 30;
 case FEB -&gt; (isLeapYear)? 29: 28;
 case JAN, MAR, MAY, JUL, AUG, OCT, DEC -&gt; 31;
 };
}
</code></pre>
Example 2: Doesn't returns value.
<pre><code>public static void printNoOfDaysInAMonth(Month month, boolean isLeapYear) {
 switch(month) {
 case APR, JUN, SEP, NOV -&gt; {
 System.out.println(&quot;30 days&quot;);
 }
 case FEB -&gt; {
 System.out.println(((isLeapYear)? 29: 28) + &quot; days&quot;);
 }
 case JAN, MAR, MAY, JUL, AUG, OCT, DEC -&gt; {
 System.out.println(&quot;31 days&quot;);
 }
 };
}
</code></pre>
Reference
<a href="https://docs.oracle.com/en/java/javase/15/language/switch-expressions.html" rel="nofollow noreferrer">Switch Expressions</a>

blocks|key|3105402|text|以这样的方式编写someMethod()：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3105403|public+void+someMethod()+{

++++SomeClass.AnotherClass.MyEnum+enumExample+=+SomeClass.AnotherClass.MyEnum.VALUE_A;

++++switch+(enumExample)+{
++++case+VALUE_A:
++++++++break;
++++}

}|code-block|syntax|javascript|3105404|在switch语句中，只能使用常量名称。|3105405|entityMap^0|8|C|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

Write <code>someMethod()</code> in this way:

<pre><code>public void someMethod() {

 SomeClass.AnotherClass.MyEnum enumExample = SomeClass.AnotherClass.MyEnum.VALUE_A;

 switch (enumExample) {
 case VALUE_A:
 break;
 }

}
</code></pre>

In switch statement you must use the constant name only.

First I'll state that I'm much more familiar with enums in C# and it seems like enums in java is a quite mess.

As you can see, I'm trying to use a switch statement @ enums in my next example but I always get an error no matter what I'm doing.

The error I receive is:

<blockquote>
 The qualified case label <code>SomeClass.AnotherClass.MyEnum.VALUE_A</code> must be replaced with the unqualified enum constant <code>VALUE_A</code>
</blockquote>

The thing is I quite understand the error but I can't just write the VALUE_A since the enum is located in another sub-class. Is there a way to solve this problem? And why is it happening in Java?

<pre><code>//Main Class
public class SomeClass {

 //Sub-Class
 public static class AnotherClass {
 public enum MyEnum {
 VALUE_A, VALUE_B
 } 
 public MyEnum myEnum;
 }

 public void someMethod() { 
 MyEnum enumExample //...

 switch (enumExample) {
 case AnotherClass.MyEnum.VALUE_A: { &lt;-- error on this line
 //..
 break;
 }
 }
 }
}
</code></pre>

Java: using switch statement with enum under subclass

首先，我要说明的是，我对C#中的枚举更加熟悉，java中的枚举看起来相当混乱。如您所见，我在下一个示例中尝试使用switch语句@enum，但无论我在做什么，我都会得到一个错误。我收到的错误是：必须将限定事例标签SomeClass.AnotherClass.MyEnum.VALUE_A替换为非限定枚举常量VALUE_A问题是我非常理解这个错误，但我不能只写VALUE_A，因为枚举位于另一个子类中。

问Java:将switch语句与子类下的枚举一起使用
EN

回答 7

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问Java:将switch语句与子类下的枚举一起使用EN

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问Java:将switch语句与子类下的枚举一起使用
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