Question

我试图从构造函数传递枚举类型的引用来测试一些lambda，方法引用和Stream。当我尝试实例化类时，我在枚举上遇到错误。

public class Book {

    private String title;
    private List<String> authors; 
    private int pageCount[];
    private Year year; 
    private double height;
    private Topic topic;

    public Book (String title, ArrayList<String> author, int pageCount [], Year year, double height, Topic topic  )
    {
        this.title = title;
        this.authors = author;
        this.pageCount = pageCount; 
        this.topic = topic;
        this.year = year;
        this.height = height;
    }

    public enum Topic
    {
        MEDICINE, COMPUTING, FICTION, HISTORY

    }

    public String getTitle(){
        return title;
    }

    public List<String> getAhuthors(){
        return authors;
    }

    public int [] getPageCounts(){
        return pageCount;

    }

    public Topic getTopic()
    {
        return topic;
    }



    public Year getPubDate(){
        return year;
    }

    public double getHeight()
    {
        return height;
    }

    public static void main(String args [] )
    {


        Book nails = new Book("Fundamentals of Chinese Fingernail image", Arrays.asList("Li", "Fun", "Li"), 
                 new int [] {256}, Year.of(2014), 25.2, COMPUTING);

        Topic test = Topic.COMPUTING;

        System.out.println(test);
    }
}

这就是我得到的：

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
     COMPUTING cannot be resolved to a variable at Book.main(Book.java:70)

Answer 1

替换

Book nails = new Book("Fundamentals of Chinese Fingernail image", Arrays.asList("Li", "Fun", "Li"), 
             new int [] {256}, Year.of(2014), 25.2, COMPUTING);

通过

Book nails = new Book("Fundamentals of Chinese Fingernail image", Arrays.asList("Li", "Fun", "Li"), 
             new int [] {256}, Year.of(2014), 25.2, Topic.COMPUTING);

编辑：

就像@Voltboyy指出的那样，你必须更改我之前指出的qhat并将构造函数中的ArrayList<String>替换为List<String>，如下所示：

public Book(String title, List<String> list, int pageCount[], Year year, double height, Topic topic) {
    this.title = title;
    this.authors = list;
    this.pageCount = pageCount;
    this.topic = topic;
    this.year = year;
    this.height = height;
}

你的程序会运作。

Answer 2

正如@djointster所说，COMPUTING应为Topic.COMPUTING。

但是，由于private List<String> authors与构造函数中的ArrayList<String> author不同，您的代码仍无效。

所以你应该改变这个：

ArrayList<String> authors;
//to
List<String> authors;

在构造函数中。

Java枚举作为构造函数传递

2 个答案: