Strange behavior with Java enums -


i run strange behavior java enums. if write next enum:

public enum test {    public static final int c1 = 5; }

you got compilation error, expected because did not declare enum constants in beginning.

but strange part if add semicolon without constant name in beginning:

public enum test {    ;    public static final int c1 = 5; }

your code compiled successfully.

maybe question dumb , there answer in java specification have not found 1 yet.

if understands why java compiler so, please explain.

as answer pointed out, relevant section of jls 8.9, 8.9.1 states:

the body of enum declaration may contain enum constants. enum constant defines instance of enum type.

enumbody:
{ [enumconstantlist] [,] [enumbodydeclarations] }

to understand meaning of enumbody definition 1 must @ jls chapter 2.4, grammar notation, says

the syntax {x} on right-hand side of production denotes 0 or more occurrences of x.

also

the syntax [x] on right-hand side of production denotes 0 or 1 occurrences of x. is, x optional symbol. alternative contains optional symbol defines 2 alternatives: 1 omits optional symbol , 1 includes it.

how relate question? means valid enum declarations following (some grammar notation follows, bear me):

public enum test { }  public enum test {   [enumconstantlist] }  public enum test {   [enumconstantlist] , }  public enum test {  , }  public enum test {   [enumbodydeclarations] }  public enum test {  , [enumbodydeclarations] }  public enum test {   [enumconstantlist] [enumbodydeclarations] }  public enum test {   [enumconstantlist] , [enumbodydeclarations] }

[enumconstantlist] not interesting because it's 1 expect:

enumconstant {, enumconstant}

that is, 1 or more enumconstant separated commas (i'm not going definition of enumconstant, i've fallen deep enough rabbit hole plus it's not relevant question).

things interesting (finally) definition of [enumbodydeclarations]:

enumbodydeclarations:
; {classbodydeclaration}

this why first example invalid

you incorrectly specified enumbodydeclarations above excerpt shows non-optional semicolon followed 0 or more classbodydeclaration.

this why second example valid

it contains non-optional semicolon followed valid classbodydeclaration.

phew.

this means following valid enum declarations:

public enum test {  ; }  public enum test {  ,; }  public enum test {    ,;    public static final int c1 = 5; }  public enum test {    cat, }  public enum test {    cat; }  public enum test {    cat,; }  public enum test {    cat,;    public static final int c1 = 5; }  public enum test {    cat;    public static final int c1 = 5; }

but never

public enum test {    cat,    public static final int c1 = 5; }

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