构造函数枚举错误

Question

public enum ProductCategory {
  FOOD, BEVERAGE, DEFAULT;

private final String label;

private ProductCategory(String label){
this.label = label;
}

public String getLabel(){
        return label;
}

I want to implement method getLabel() in this enum class, but I am gettin error: "The constructor ProductCategory() is undefined".

I already have constructor that I need, what else I need to write? I tried to write default constructor but again I am getting error.

PS I am total beginner in java.

Answer 1

错误来自enum成员的声明：由于构造函数采用String label ，因此您需要提供字符串以传递给该构造函数：

FOOD("food"), BEVERAGE("bev"), DEFAULT("[default]");

Answer 2

The only constructor you've currently got requires a string to be passed in - but all the enum values ( FOOD , BEVERAGE , DEFAULT ) don't specify strings, so they can't call the constructor.

Two options:

• Add a parameterless constructor:

   private ProductCategory() {} 

  This wouldn't associate labels with your enum values though.

• Specify the label on each value:

   FOOD("Food"), BEVERAGE("Beverage"), DEFAULT("Default"); 

The latter is almost certainly what you want.

Answer 3

Enum constructor can be called while declaring the Enum members itself.

public enum ProductCategory
    {
        FOOD("label1"),
        BEVERAGE("label2"),
        DEFAULT("label3");

        private final String label;

        ProductCategory(String label)
        {
            this.label = label;
        }

        public String getLabel()
        {
            return label;
        }
    }

Answer 4

public enum ProductCategory {
    FOOD("FOOD"), BEVERAGE("BEVERAGE"), DEFAULT("DEFAULT");

    private final String label;

    private ProductCategory(String label) {
        this.label = label;
    }

    public String getLabel() {
        return label;
    }
}