Java switch statement Constant expression required but it IS constant

Question

So  I am working on this class that has a few static constants   public abstract class Foo               public static final int BAR      public static final int BAZ      public static final int BAM              Then  I would like a way to get a relevant string based on the constant   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             However  when I compile  I get a constant expression required 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 Foo BA  constant

User · Answer

Below code is self-explanatory  We can use an enum with a switch case              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            Based on the class values from the enum can be mapped    switch  ClassNames valueOf clazz getSimpleName               case STRING              String castValue    String  keyValue              break          case BOOLEAN              break          case Integer              break          case LONG              break          default              isValid   false           Hope it helps

User · Answer

If you re using it in a switch case then you need to get the type of the enum even before you plug that value in the switch  For instance       SomeEnum someEnum   SomeEnum values   1     switch  someEnum                case GRAPES              case BANANA        And the enum is like   public enum SomeEnum        GRAPES  Grapes   0       BANANA  Banana   1        private String typeName      private int typeId       SomeEnum String typeName  int typeId           this typeName   typeName          this typeId   typeId

User · Answer

I recommend using the following way   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

User · Answer

Sometimes the switch variable can also make that error for example   switch view getTag       which is an Object type     case 0   will give compiler error that says Constant expression required               To solve you should cast the variable to int in this case   So   switch  int view getTag       will be int     case 0    No Error

User · Answer

Because those are not compile time constants   Consider the following valid code   public static final int BAR   new Random   nextInt      You can only know the value of BAR in runtime

User · Answer

In my case  I was getting this exception because  switch  tipoWebServ                                case VariablesKmDialog OBTENER KM                                  resultObtenerKm result                                   break                              case var MODIFICAR KM                                  resultModificarKm result                                   break                              in the second case I was calling the constant from the instance var MODIFICAR KM  but I should use VariablesKmDialog OBTENER KM directly from the class

User · Answer

You get Constant expression required because you left the values off your constants  Try   public abstract class Foo               public static final int BAR 0      public static final int BAZ 1      public static final int BAM 2

User · Answer

You can use an enum like in this example   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                Source  Switch statement with enum

User · Answer

I understand that the compiler needs the expression to be known at compile time to compile a switch  but why isn t Foo BA  constant    While they are constant from the perspective of any code that executes after the fields have been initialized  they are not a compile time constant in the sense required by the JLS  see   15 28 Constant Expressions for the specification of a constant expression1   This refers to   4 12 4 Final Variables which defines a  constant variable  as follows      We call a variable  of primitive type or type String  that is final and initialized with a compile-time constant expression    15 28  a constant variable  Whether a variable is a constant variable or not may have implications with respect to class initialization    12 4 1   binary compatibility    13 1    13 4 9  and definite assignment    16     In your example  the Foo BA  variables do not have initializers  and hence do not qualify as  constant variables    The fix is simple  change the Foo BA  variable declarations to have initializers that are compile-time constant expressions   In other examples  where the initializers are already compile-time constant expressions   declaring the variable as final may be what is needed   You could change your code to use an enum rather than int constants  but that brings another couple of different restrictions    You must include a default case  even if you have case for every known value of the enum  see Why is default required for a switch on an enum  The case labels must all be explicit enum values  not expressions that evaluate to enum values      1 - The constant expression restrictions can be summarized as follows    Constant expressions a  can use primitive types and String only  b  allow primaries that are literals  apart from null  and constant variables only  c  allow constant expressions possibly parenthesised as subexpressions  d  allow operators except for assignment operators      -- or instanceof  and e  allow type casts to primitive types or String only   Note that this doesn t include any form of method or lambda calls  new   class   length or array subscripting   Furthermore  any use of array values  enum values  values of primitive wrapper types  boxing and unboxing are all excluded because of a

User · Answer

I recommend you to use enums     Check this out   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            Then you can use it like this   System out println Foo BAR getDescription

User · Answer

Got this error in Android while doing something like this    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                  despite declaring a constant   public static final String  ADMIN CONSTANT   Admin    I resolved the issue by changing my code to this   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

User · Answer

This was answered ages ago and probably not relevant  but just in case  When I was confronted with this issue  I simply used an if statement instead of switch  it solved the error  It is of course a workaround and probably not the  quot right quot  solution  but in my case it was just enough  Edit  2021 01 21 This Answer is a bit misleading  And I would like to clarify it   Replacing a switch statement with an if should not be considered as a goto solution  there are very good reasons why both concepts of switch and if exist in software development  as well as performance matters to consider when choosing between the two  Although I provide a solution to the presented error  My answer sheds no light on  quot why quot  the problem occurs but instead offers a way around the problem   In my specific case  using an if statement instead was just enough to solve the problem  Developers should take the time and decide if this is the right solution for the current problem you have at hand  Thus this answer should be considered solely as a workaround in specific cases as stated in my first response  and by no means as the correct answer to this question

User · Answer

I got this error on Android  and my solution was just to use   public static final int TAKE PICTURE   1    instead of   public static int TAKE PICTURE   1

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

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