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Java enum: Refactoring operator statements "constant expression required" compilation error?

I have a class declaring constants for my application

public class GroupConstants { .. public static final int INTEGER_VALUE = 1; public static final int LONG_VALUE = 2; public static final int STRING_VALUE = 3; .. }

The code has a set of switch statements

 private static Object getValue(String stringValue, Parameter parameter) throws InvalidPatternException { Object result=null; switch (parameter.getDataType()) { case GroupConstants.STRING_VALUE: // String value result=stringValue; break; case GroupConstants.INTEGER_VALUE: // Long value case GroupConstants.LONG_VALUE: case GroupConstants.BOOLEAN_VALUE: case GroupConstants.DATE_VALUE: .. }

I want to reorganize constant int values ​​that will be represented by an enumeration

 public enum DataType { UNKNOWN_VALUE(0,"unknown"), INTEGER_VALUE(1,"integer"), LONG_VALUE(2,"long"), STRING_VALUE(3,"string"), BOOLEAN_VALUE(4,"boolean"), .. }

so my code might look like this:

 @Deprecated public static final int INTEGER_VALUE = DataType.INTEGER_VALUE.getId();

and overtime, I can change my switch statements. When I change the static final reference to int to indicate an enumeration, all of my switch statements are interrupted.

 [javac] /home/assure/projects/tp/main/src/a/b/c/DDDDDManagerBean.java:1108: constant expression required [javac] case GroupConstants.INTEGER_VALUE: [javac] ^ [javac] /home/assure/projects/tp/main/src/a/b/c/ParameterComponent.java:203: constant expression required [javac] case GroupConstants.INTEGER_VALUE: [javac] ^ [javac] /home/assure/projects/tp/main/src/a/b/c/ParameterComponent.java:268: constant expression required [javac] case GroupConstants.INTEGER_VALUE: [javac] ^ [javac] /home/assure/projects/tp/main/src/a/b/c/ParameterComponent.java:316: constant expression required [javac] case GroupConstants.INTEGER_VALUE: [javac] ^ [javac] /home/assure/projects/tp/main/src/a/b/c/ParameterComponent.java:436: constant expression required [javac] case GroupConstants.INTEGER_VALUE:

I don’t want to be forced to change all the switches, so is there any clean work there?

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4 answers

This will not work. The problem is that calling getId() means that the constant expression is not a JLS compile-time constant expression. See JLS 15.28 Constant Expressions for details and you will see that method calls are not allowed in constant expressions.

I don’t think there is any workaround other than a large-scale change of all switch statements. But I would not worry. Your IDE should help you find and replace all occurrences of old constants.

Followup

The following code from your comment will not work:

 private int INTEGER_VALUE_HOLDER = DataType.INTEGER_VALUE.getId(); public static final int INTEGER_VALUE = INTEGER_VALUE_HOLDER;

First, INTEGER_VALUE_HOLDER not a "constant variable" as defined in JLS 4.12.4 Final Variables . Therefore, not INTEGER_VALUE .

Secondly, an initializer expression for static cannot refer to this , and INTEGER_VALUE_HOLDER is really a different way of saying this.INTEGER_VALUE_HOLDER .

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Java has built-in enumeration support in switch statements. In your case, you should say:

 DataType type = ...; switch (type) { case UNKNOWN_VALUE //do something break; case INTEGER_VALUE //do something break; case LONG_VALUE //do something break; case STRING_VALUE //do something break; case BOOLEAN_VALUE //do something break;
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Try to get rid of the GroupConstants. prefix GroupConstants. in your case statements. For reasons completely incomprehensible to me, it does not accept the same constant if it has a prefix with the class name.

So instead

  case GroupConstants.STRING_VALUE:

try:

  case STRING_VALUE:

It may require static import to compile it.

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in eclipse the IDE is simple, in the CTRL + 1 clause and the switch switch clause - if-else clause http://tools.android.com/tips/non-constant-fields

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