如何在参数化构造函数中使用枚举？

Question

I have an assignment that asks me to create enumeration types. My question is, after I initialize them, how do I bring them into the default and parameterized constructors? i tried the following but it doesn't work... any ideas? Thanks

package magazine;
import paperPublication.PaperPublication;


public class Magazine extends PaperPublication {

    private enum paperQuality {LOW, NORMAL, HIGH};
    private enum issuingFrequency {WEEKLY, MONTHLY, YEARLY};

    public Magazine() {
        paperQuality = null;   //doesn't work
        issuingFrequency = null;    //doesn't work
    }

    public Magazine (double price, int numberOfPages, enum paperQuality  //doesn't work, enum issuingFrequency  //doesn't work) {

    }
}

Answer 1

This is a type definition:

private enum paperQuality ...

But you don't actually have a field of that type declared. Try something like this:

private enum PaperQuality {...};
private PaperQuality paperQuality;

The first line defines the PaperQuality enum, defining the various values that any PaperQuality can hold. The second line creates a private field that is of that type, named paperQuality . The constructor could look like this:

public Magazine (double price, int numberOfPages, PaperQuality paperQuality) {
    ...
    this.paperQuality = paperQuality;
}

Answer 2

You've declared the type but not the instance. You'll want...

        public enum PaperQuality {LOW, NORMAL, HIGH};
        public enum IssuingFrequency {WEEKLY, MONTHLY, YEARLY};

        PaperQuality paperQuality;
        IssuingFrequency issuingFrequency;

        public Magazine() {
            paperQuality = null; 
            issuingFrequency = null; 
        }

        public Magazine (double price, int numberOfPages, PaperQuality paperQuality){
          //logic here
        }

I suggest you read a tutorial on Java enums.

Answer 3

enum keyword is like class keyword: it defines a type, not a variable.

You code is similar to the following:

public class Magazine extends PaperPublication {

   private class paperQuality { /* something */ }; // note class instead of enum
   private class issuingFrequency { /* something */ };

   public Magazine() {
       paperQuality = null;   //doesn't work -- beacuse paperQuality is a class
       paperQuality a; // does work because class name is suitable for variable definition
       a = null; // you can assign null to class variables

Answer 4

For instance, you can create enum in the body of class

enum Sex {
    MALE,
    FEMALE
}

Also, you can create a separate class. Then declare the variable with enum type,and in the parentheses of the constructor, specify the type that you created

private Sex enSex;
private String personName;
private int personAge;
private double personWeight;

public Person(String name, int age, double weight, Sex enSex) {
    this.personName = name;
    this.personAge = age;
    this.personWeight = weight;
    this.enSex = enSex;
}

Answer 5

private enum paperQuality {LOW, NORMAL, HIGH};
private enum issuingFrequency {WEEKLY, MONTHLY, YEARLY};

First create a variable for the enum type.

paperQuality paperqual;
issuingFrequency issuingfre;

then you can use those enum variable to assign values

public Magazine() {
    paperqual= null;  
    issuingfre= null;   
}

public Magazine (paperQuality pq,issuingFrequency isq) {
   paperqual = pq;
   issuingfre = isq;
}

Answer 6

Declare a variable of the enumerated type:

private paperQuality quality;

( enum paperQuality { ... } just defines the enum type, it does not create a variable!).

Also, you cannot assign null to an enumerated type, it must be one of the enumerated values (ie LOW ).

Answer 7

enum isn't a datatype its more like the "class" keyword. The datatypes in your example are paperQuality and issuingFrequency. So:

public Magazine (double price,
     int numberOfPages,
     paperQuality quality,
     issuingFrequency freq) {

}