blocks|key|916068|text|因为这些不是编译时间常量。考虑以下有效代码：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|916069|public+static+final+int+BAR+=+new+Random().nextInt();|code-block|syntax|javascript|916070|只有在运行时才能知道BAR的值。|offset|length|style|CODE|916071|entityMap^0|0|0|A|3|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|$]]

Because those are not compile time constants. Consider the following valid code:

<pre><code>public static final int BAR = new Random().nextInt();
</code></pre>

You can only know the value of <code>BAR</code> in runtime.

blocks|key|1130858|text|您可以使用如下示例中的枚举：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1130859|public+class+MainClass+{
enum+Choice+{+Choice1,+Choice2,+Choice3+}
public+static+void+main(String[]+args)+{
Choice+ch+=+Choice.Choice1;

switch(ch)+{
++case+Choice1:
++++System.out.println("Choice1+selected");
++++break;
+case+Choice2:
+++System.out.println("Choice2+selected");
+++break;
+case+Choice3:
+++System.out.println("Choice3+selected");
+++break;
++++}
++}
}|code-block|syntax|javascript|1130860|来源：Switch+statement+with+enum|offset|length|1130861|entityMap|0|LINK|mutability|MUTABLE|url|http://www.java2s.com/Tutorial/Java/0040__Data-Type/Switchstatementwithenum.htm^0|0|0|3|Q|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

You can use an enum like in this example:

<pre><code>public class MainClass {
enum Choice { Choice1, Choice2, Choice3 }
public static void main(String[] args) {
Choice ch = Choice.Choice1;

switch(ch) {
 case Choice1:
 System.out.println("Choice1 selected");
 break;
 case Choice2:
 System.out.println("Choice2 selected");
 break;
 case Choice3:
 System.out.println("Choice3 selected");
 break;
 }
 }
}
</code></pre>

Source:
<a href="http://www.java2s.com/Tutorial/Java/0040__Data-Type/Switchstatementwithenum.htm" rel="noreferrer">Switch statement with enum</a>

blocks|key|1130892|text|我建议您使用枚举:)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1130893|看看这个：|1130894|public+enum+Foo+
{
++++BAR("bar"),
++++BAZ("baz"),
++++BAM("bam");

++++private+final+String+description;

++++private+Foo(String+description)
++++{
++++++++this.description+=+description;
++++}

++++public+String+getDescription()
++++{
++++++++return+description;
++++}
}|code-block|syntax|javascript|1130895|然后你可以像这样使用它：|1130896|System.out.println(Foo.BAR.getDescription());|1130897|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I recommend you to use enums :)

Check this out:

<pre><code>public enum Foo 
{
 BAR("bar"),
 BAZ("baz"),
 BAM("bam");

 private final String description;

 private Foo(String description)
 {
 this.description = description;
 }

 public String getDescription()
 {
 return description;
 }
}
</code></pre>

Then you can use it like this:

<pre><code>System.out.println(Foo.BAR.getDescription());
</code></pre>

blocks|key|916163|text|我在Android上得到了这个错误，我的解决方案是使用：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|916164|public+static+final+int+TAKE_PICTURE+=+1;|code-block|syntax|javascript|916165|而不是|916166|public+static+int+TAKE_PICTURE+=+1;|916167|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|$]]

I got this error on Android, and my solution was just to use:

<pre><code>public static final int TAKE_PICTURE = 1;
</code></pre>

instead of 

<pre><code>public static int TAKE_PICTURE = 1;
</code></pre>

blocks|key|1130978|text|在Android中执行类似以下操作时遇到此错误：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1130979|+roleSpinner.setOnItemSelectedListener(new+AdapterView.OnItemSelectedListener()+{
++++++++@Override
++++++++public+void+onItemSelected(AdapterView<?>+parent,+View+view,+int+position,+long+id)+{

++++++++++++switch+(parent.getItemAtPosition(position))+{
++++++++++++++++case+ADMIN_CONSTANT:+//Threw+the+error

++++++++++++}|code-block|syntax|javascript|1130980|尽管声明了一个常量：|1130981|public+static+final+String++ADMIN_CONSTANT=+"Admin";|offset|length|style|CODE|1130982|我通过将代码更改为以下代码解决了此问题：|1130983|roleSpinner.setOnItemSelectedListener(new+AdapterView.OnItemSelectedListener()+{
++++++++@Override
++++++++public+void+onItemSelected(AdapterView<?>+parent,+View+view,+int+position,+long+id)+{

++++++++++++String+selectedItem+=+String.valueOf(parent.getItemAtPosition(position));
++++++++++++switch+(selectedItem)+{
++++++++++++++++case+ADMIN_CONSTANT:

++++++++++++}|1130984|entityMap^0|0|0|0|0|1G|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|X|8|@$K|Y|L|Z|M|N]]|9|@]|A|$]]|$1|O|3|P|5|6|7|10|8|@]|9|@]|A|$]]|$1|Q|3|R|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

Got this error in Android while doing something like this:

<pre><code> roleSpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
 @Override
 public void onItemSelected(AdapterView&lt;?&gt; parent, View view, int position, long id) {

 switch (parent.getItemAtPosition(position)) {
 case ADMIN_CONSTANT: //Threw the error

 }
</code></pre>

despite declaring a constant:

<code>public static final String ADMIN_CONSTANT= "Admin";</code>

I resolved the issue by changing my code to this:

<pre><code>roleSpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
 @Override
 public void onItemSelected(AdapterView&lt;?&gt; parent, View view, int position, long id) {

 String selectedItem = String.valueOf(parent.getItemAtPosition(position));
 switch (selectedItem) {
 case ADMIN_CONSTANT:

 }
</code></pre>

blocks|key|1131001|text|在我的例子中，我得到这个异常是因为|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1131002|switch+(tipoWebServ)+{
++++++++++++++++++++++++++++case+VariablesKmDialog.OBTENER_KM:
++++++++++++++++++++++++++++++++resultObtenerKm(result);
++++++++++++++++++++++++++++++++break;
++++++++++++++++++++++++++++case+var.MODIFICAR_KM:
++++++++++++++++++++++++++++++++resultModificarKm(result);
++++++++++++++++++++++++++++++++break;
++++++++++++++++++++++++}|code-block|syntax|javascript|1131003|在第二种情况下，我从实例var.MODIFICAR_KM:调用常量，但我应该直接从类中使用VariablesKmDialog.OBTENER_KM。|offset|length|style|CODE|1131004|entityMap^0|0|0|C|H|19|S|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]|$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|N|$]]

In my case, I was getting this exception because

<pre><code>switch (tipoWebServ) {
 case VariablesKmDialog.OBTENER_KM:
 resultObtenerKm(result);
 break;
 case var.MODIFICAR_KM:
 resultModificarKm(result);
 break;
 }
</code></pre>

in the second case I was calling the constant from the instance <code>var.MODIFICAR_KM:</code> but I should use <code>VariablesKmDialog.OBTENER_KM</code> directly from the class.

blocks|key|1131043|text|下面的代码是不言自明的，我们可以使用带有切换大小写的枚举：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1131044|/**
+*
+*/
enum+ClassNames+{
++++STRING(String.class,+String.class.getSimpleName()),
++++BOOLEAN(Boolean.class,+Boolean.class.getSimpleName()),
++++INTEGER(Integer.class,+Integer.class.getSimpleName()),
++++LONG(Long.class,+Long.class.getSimpleName());
++++private+Class+typeName;
++++private+String+simpleName;
++++ClassNames(Class+typeName,+String+simpleName){
++++++++this.typeName+=+typeName;
++++++++this.simpleName+=+simpleName;
++++}
}|code-block|syntax|javascript|1131045|基于来自枚举的类值可以映射：|1131046|+switch+(ClassNames.valueOf(clazz.getSimpleName()))+{
++++++++case+STRING:
++++++++++++String+castValue+=+(String)+keyValue;
++++++++++++break;
++++++++case+BOOLEAN:
++++++++++++break;
++++++++case+Integer:
++++++++++++break;
++++++++case+LONG:
++++++++++++break;
++++++++default:
++++++++++++isValid+=+false;

++++}|1131047|希望它能有所帮助:)|1131048|entityMap^0|0|0|0|0|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]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Below code is self-explanatory,
We can use an enum with a switch case:

<pre><code>/**
 *
 */
enum ClassNames {
 STRING(String.class, String.class.getSimpleName()),
 BOOLEAN(Boolean.class, Boolean.class.getSimpleName()),
 INTEGER(Integer.class, Integer.class.getSimpleName()),
 LONG(Long.class, Long.class.getSimpleName());
 private Class typeName;
 private String simpleName;
 ClassNames(Class typeName, String simpleName){
 this.typeName = typeName;
 this.simpleName = simpleName;
 }
}
</code></pre>

Based on the class values from the enum can be mapped:

<pre><code> switch (ClassNames.valueOf(clazz.getSimpleName())) {
 case STRING:
 String castValue = (String) keyValue;
 break;
 case BOOLEAN:
 break;
 case Integer:
 break;
 case LONG:
 break;
 default:
 isValid = false;

 }
</code></pre>

Hope it helps :)

blocks|key|1131092|text|我推荐使用以下方式：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1131093|public+enum+Animal+{
++++DOG("dog"),+TIGER("tiger"),+LION("lion");
++++private+final+String+name;

++++@Override
++++public+String+toString()+{
++++++++return+this.name;
++++}
}


public+class+DemoSwitchUsage+{

+++++private+String+getAnimal(String+name)+{
+++++++++Animal+animalName+=+Animal.valueOf(name);
+++++++++switch(animalName)+{
+++++++++case+DOG:
+++++++++++++//+write+the+code+required.
+++++++++++++break;
+++++++++case+LION:
+++++++++++++//+Write+the+code+required.
+++++++++++++break;
+++++++++default:
+++++++++++++break;
+++++++++}
+++++}
}|code-block|syntax|javascript|1131094|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|$]]

I recommend using the following way:

<pre><code>public enum Animal {
 DOG("dog"), TIGER("tiger"), LION("lion");
 private final String name;

 @Override
 public String toString() {
 return this.name;
 }
}


public class DemoSwitchUsage {

 private String getAnimal(String name) {
 Animal animalName = Animal.valueOf(name);
 switch(animalName) {
 case DOG:
 // write the code required.
 break;
 case LION:
 // Write the code required.
 break;
 default:
 break;
 }
 }
}
</code></pre>

blocks|key|916378|text|问题出在int和Integer上(我不知道为什么)，把int改成string，它就能工作了。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|916379|public+abstract+class+Foo+{
++++...
++++public+static+final+String+BAR;
++++public+static+final+String+BAZ;
++++public+static+final+String+BAM;
++++...
}
public+static+String+lookup(String+constant)+{
++++switch+(constant)+{
++++++++case+Foo.BAR:+return+"bar";
++++++++case+Foo.BAZ:+return+"baz";
++++++++case+Foo.BAM:+return+"bam";
++++++++default:+return+"unknown";
++++}
}|code-block|syntax|javascript|916380|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|$]]

The problem is with the int and Integer (i do not why), change the int to string and it work's
<pre><code>public abstract class Foo {
 ...
 public static final String BAR;
 public static final String BAZ;
 public static final String BAM;
 ...
}
public static String lookup(String constant) {
 switch (constant) {
 case Foo.BAR: return &quot;bar&quot;;
 case Foo.BAZ: return &quot;baz&quot;;
 case Foo.BAM: return &quot;bam&quot;;
 default: return &quot;unknown&quot;;
 }
}
</code></pre>

So, I am working on this class that has a few static constants:

<pre><code>public abstract class Foo {
 ...
 public static final int BAR;
 public static final int BAZ;
 public static final int BAM;
 ...
}
</code></pre>

Then, I would like a way to get a relevant string based on the constant:

<pre><code>public static String lookup(int constant) {
 switch (constant) {
 case Foo.BAR: return "bar";
 case Foo.BAZ: return "baz";
 case Foo.BAM: return "bam";
 default: return "unknown";
 }
}
</code></pre>

However, when I compile, I get a <code>constant expression required</code> error on each of the 3 case labels.

I understand that the compiler needs the expression to be known at compile time to compile a switch, but why isn't <code>Foo.BA_</code> constant?

Java switch statement: Constant expression required, but it IS constant

编译器

Android

所以，我正在处理这个类，它有几个静态常量：public abstract class Foo {    ...    public static final int BAR;    public static final int BAZ;    public static final int BAM;    ...}然...

问Java switch语句:需要常量表达式，但它是常量
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