Enum class member with interface cannot find methods internally

问题

I'm having a strange issue which I'm not sure if it's a compiler problem or my understanding of enums with interfaces. I'm using IntelliJ IDEA 12, building an Android project, and I have a class like this:

public class ClassWithEnum {
    private MyEnum myEnum;

    //Trying to access it internally here throws the error
    public boolean isActionable() {
        return myEnum.isActionable();
    }

    public enum MyEnum implements Action {
        ACTIONABLE() {
            @Override
            public boolean isActionable() { return true; }
        },
        NOT_ACTIONABLE() {
            @Override
            public boolean isActionable() { return false; }
        }
    }

    public interface Action {
        public boolean isActionable();
    }
}

Now, this was working initially, but now the compiler is complaining (and I've tried this in a brand new project as well with the same results) with the error:

java: /Users/kcoppock/Documents/Projects/EnumInterfaceTest/src/com/example/EnumInterfaceTest/ClassWithEnum.java:11: cannot find symbol
symbol  : method isActionable()
location: class com.example.EnumInterfaceTest.ClassWithEnum.MyEnum

I've done this before (enumerations with behaviors defined by an interface) with no issues. Any thoughts?

回答1:

You need to implement isActionable() method in MyEnum itself. Because the method isActionable() defined inside the ACIONABLE and NOT_ACTIONABLE are local to them . So you need the global method for the MyEnum enum .

use this code instead:

public enum MyEnum implements Action {
        ACTIONABLE() {
            @Override
            public boolean isActionable() { return true; }
        },
        NOT_ACTIONABLE() {
            @Override
            public boolean isActionable() { return false; }
        };
        @Override
        public boolean isActionable() { return false;}
    }

回答2:

You could try this alternative:

   public enum MyEnum implements Action {
        ACTIONABLE(true), 
        NOT_ACTIONABLE(false);

        private final boolean actionable;

        MyEnum(boolean actionable) {
           this.actionable = actionable;
        }

        @Override
        public boolean isActionable() { 
           return this.actionable; 
        }
    }

回答3:

That looks like a javac bug. javac compiles it fine in JDK7. It doesn't in JDK6 (javac 1.6.0_24), both from IntelliJ and from the command line.

回答4:

It seems that javac for 1.6 requires a global override for the interface method, whereas later versions do not, nor does the Eclipse compiler.

Seems it was just a bug with IntelliJ. I changed the compiler setting from javac to Eclipse, then back to javac and it compiles and runs as expected.

False alarm. :)

回答5:

Some people already answered this perfectly, I just add one more little tip: you can also keep the method abstract in the interface:

public enum MyEnum implements Action {
    ACTIONABLE() {
        @Override
        public boolean isActionable() { return true; }
    },
    NOT_ACTIONABLE() {
        @Override
        public boolean isActionable() { return false; }
    };
    @Override
    abstract public boolean isActionable();
}

来源：https://stackoverflow.com/questions/14570746/enum-class-member-with-interface-cannot-find-methods-internally