Java OCP study Guide: enum

[Nico van de Kamp]

Hello,

I try to find out why I can't combine two enums with a constructor value and an abstract method;

This is compiling and running:

interface Weather { int getAverageTemperature();}

enum ComplexEnumSeason implements Weather {
    WINTER("Low") {
        @Override
        public int getAverageTemperature() { return -1; }
        @Override public String getHours() { return this.toString().toLowerCase() + " 10am - 3pm";}
    },
    SUMMER("High") {
        @Override public int getAverageTemperature() { return 25;}
        public String getHours() { return "9am - 7pm";}
    },
    SPRING("Medium") {
        @Override
        public int getAverageTemperature() { return 18;}
        public String getHours() { return this.toString() + " 9am - 5pm";}
    },
    FALL("Medium") {
        @Override
        public int getAverageTemperature() {return 18;}
        @Override  public String getHours() { return this.toString() + "9am - 5pm";}
    };

    private final String expectedVisitors;                  // instance variabele

    private ComplexEnumSeason(String expectedVisitors) {    // Constructor, welke private is
        this.expectedVisitors = expectedVisitors;
    }
    public void printExpectedVisitors() {                   // Method
        System.out.println(expectedVisitors);
    }

    public abstract String getHours();
}

But now I want to combine the enum value's SPRING and FALL, because they have for example the same values:

enum ComplexEnumSeason implements Weather {

   // removed the single SPRING and keep SUMMER, WINTER

   SPRING. FALL("Medium") {
        @Override
        public int getAverageTemperature() {return 18;}
        @Override  public String getHours() { return this.toString() + "9am - 5pm";}
    };

   // the rest is all the same
   //

This doesn't compile
I've tried a lot of different things but everytime compiling errors. I couldn't find out what the right way.
They gave an another example but than without constructor values like "Low", "Medium", that is compiling

[Campbell Ritchie]

You would have to go through the JLS (=Java® Language Specification)←click this link to check what the grammar is. I suspect that declaring a constructor for the class and calling it via WINTER, SUMMER, and FALL means that the class underlying the enum only has a one‑argument constructor, and you are not calling that constructor via SPRING. SPRING would then expect to use a no‑arguments constructor. At least I think that is the problem.
The precedence of () is higher than that of comma, so the () after FALL are not applicable to SPRING.

[Nico van de Kamp]

Thanks Ritchie, I understand this, in how I the code have that is a problem.

Next example from Java 17 Study Guide, is working but without constructor value with SPRING and FALL put together:

enum EnumsSeason {
    WINTER {
        public String getHours() { return "10am-3pm"; }
    },
    SUMMER {
        public String getHours() { return "9am-7pm"; }
    },
   SPRING, FALL;
    public String getHours() { return "9am-5pm"; }
}

But is this also possible with a constructor value? I've been through that site of Oracle but there they don't have situation with a constructor and combine two or more enum values with implementing one or more methods.

...
SPRING, FALL("medium");
    public String getHours() { return "9am-5pm"; }

My expectation is that two enum objects will be created with the same constructor value "medium" and both implemented with same method...

But maybe is this not possible...

[Paul Clapham]

If the compiler had problems with

SPRING, FALL("medium");
    public String getHours() { return "9am-5pm"; }

then I might have a try with

SPRING("medium"), FALL("medium");
    public String getHours() { return "9am-5pm"; }

but that would depend on what the compiler messages said.