How to define static constants in a Java enum?

Is there any way to define static final variables (effectively constants) in a Java enum declaration?

What I want is to define in one place the string literal value for the BAR(1...n) values:

@RequiredArgsConstructor
public enum MyEnum {
BAR1(BAR_VALUE),
FOO("Foo"),
BAR2(BAR_VALUE),
...,
BARn(BAR_VALUE);


private static final String BAR_VALUE = "Bar";


@Getter
private final String value;
}

I got the following error message for the code above: Cannot reference a field before it is defined.

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小开

Maybe you should considering breaking this enum into two fields: an enum and an int:

@RequiredArgsConstructor
public enum MyEnum {
BAR("Bar"),
FOO("Foo")


@Getter
private final String value;
}

And then use:

private MyEnum type;
private int value;

(You can put that into a class or not, whether it makes sense to you)

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最佳答案

As IntelliJ IDEA suggest when extracting constant - make static nested class. This approach works:

@RequiredArgsConstructor
public enum MyEnum {
BAR1(Constants.BAR_VALUE),
FOO("Foo"),
BAR2(Constants.BAR_VALUE),
...,
BARn(Constants.BAR_VALUE);






@Getter
private final String value;


private static class Constants {
public static final String BAR_VALUE = "BAR";
}
}

小开

public enum MyEnum {
BAR1(MyEnum.BAR_VALUE);


public static final String BAR_VALUE = "Bar";

works fine

小开

public enum MyEnum {
//  BAR1(       foo),   // error: illegal forward reference
//  BAR2(MyEnum.foo2),  // error: illegal forward reference
BAR3(MyEnum.foo);   // no error


public static final int foo =0;
public static       int foo2=0;
MyEnum(int i) {}


public static void main(String[] args) { System.out.println("ok");}
}

This can be done without an inner class for the constant.