Question

我有一个要求我创建枚举类型的作业。我的问题是，在我初始化它们之后，如何将它们引入默认和参数化构造函数？我试过以下但它不起作用......任何想法？感谢

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

这是一个类型定义：

private enum paperQuality ...

但是你实际上没有声明该类型的字段。尝试这样的事情：

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

第一行定义PaperQuality枚举，定义任何PaperQuality可以容纳的各种值。第二行创建一个名为paperQuality的私有字段。构造函数可能如下所示：

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

Answer 2

您已声明了类型，但未声明实例。你会想要......

        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
        }

我建议您阅读有关Java枚举的教程。

Answer 3

enum关键字与class关键字类似：它定义了类型，而不是变量。

您的代码类似于以下内容：

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

声明枚举类型的变量：

private paperQuality quality;

（enum paperQuality { ... }只定义枚举类型，它不会创建变量！）。

此外，您无法将null分配给枚举类型，它必须是枚举值之一（即LOW）。

Answer 5

例如，您可以在类

的主体中创建枚举

enum Sex {
    MALE,
    FEMALE
}

此外，您可以创建一个单独的类。然后使用枚举类型声明变量，并在构造函数的括号中指定您创建的类型

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 6

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

首先为枚举类型创建一个变量。

paperQuality paperqual;
issuingFrequency issuingfre;

然后您可以使用这些枚举变量来分配值

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

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

Answer 7

枚举不是数据类型，更像是“class”关键字。示例中的数据类型为paperQuality和issuingFrequency。所以：

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

}

如何在参数化构造函数中使用枚举？

7 个答案: