java - For-Each 循环不兼容类型

Question

我正在开发一个为电影创建虚拟数据库的项目。我有两个类:MovieEntry(用于单个电影条目)和 MovieDatabase(包含数据库并允许添加等的较大类)我收到一些错误，其中第一个错误是在 searchTitle 方法中说数据库是不兼容的类型。谁能告诉我如何执行这些 for-each 循环？我读了这本书，我认为 ArrayList 应该放在那里，但显然不是。

**import java.util.ArrayList;
import java.util.Scanner;
import java.io.*;
public class MovieDatabase
{
   private ArrayList<MovieEntry> Database = new ArrayList<MovieEntry>();
   public MovieDatabase(){
       ArrayList<MovieDatabase> Database = new ArrayList<MovieDatabase>(0);
    }

   public int countTitles() throws IOException{
   Scanner fileScan;
   fileScan = new Scanner (new File("movies.txt"));
   int count = 0;
   String movieCount;
   while(fileScan.hasNext()){
       movieCount = fileScan.nextLine();
       count++;
    }
   return count;
}

   public void addMovie(MovieEntry m){
       Database.add(m);
    }

   public ArrayList<MovieEntry> searchTitle(String substring){
       for (String title : Database)
          System.out.println(title);
          return null;
    }

   public ArrayList<MovieEntry> searchGenre(String substring){
       for (String genre : Database)
          System.out.println(genre);
          return null;
    }

   public ArrayList<MovieEntry> searchDirector (String str){
       for (String director : Database)
          System.out.println(director);
          return null;
    }

   public ArrayList<MovieEntry> searchYear (int yr){
       ArrayList <String> yearMatches = new ArrayList<String>();
       for (String s : Database)
       s.getYear();
        if(yearMatches.contains(y) == false){
           yearMatches.add(y);
        }
       return yearMatches;
    }

   public ArrayList<MovieEntry> searchYear(int from, int to){
       ArrayList <String> Matches = new ArrayList<String>();
       for(Student s : movies);
          Matches.add();
       return Matches;
    }

   public void readMovieData(String movies){
       String info;
       try{
           Scanner fileReader = new Scanner(new File(movies));
           Scanner lineReader;

           while(fileReader.hasNext()){
               info = fileReader.nextLine();

               lineReader = new Scanner(info);
               lineReader.useDelimiter(":");

               String title = lineReader.next();
               String director = lineReader.next();
               String genre = lineReader.next();
               int year = lineReader.nextInt();
            }

        }catch(FileNotFoundException error){
            System.out.println("File not found.");

        }catch(IOException error){
            System.out.println("Oops! Something went wrong.");
        }
    }



 public int countGenres(){
    String g;
    ArrayList <String> gList = new ArrayList<String>();
    for(Student s : movies){
      String g = s.getGenre();
      if(gList.contains(g) == false){
        gList.add(g);
      }
      return gList.size();
    }
    }
    public int countDirectors(){
     ArrayList <String> dList = new ArrayList<String>();
     for(Student s : movies){
        String d = s.getDirector();
        if(dList.contains(d) == false){
            dList.add(d);
        }
        return dList.size();
     }

     }

    public String listGenres(){
        ArrayList <String> genreList = new ArrayList<String>();

    }

}**

Answer 1

foreach 变量的类型( String ，在 searchTitle 方法中的循环的情况下)必须与参数化类型 ( MovieEntry ) 的类型参数 ( ArrayList<MovieEntry> ) 兼容。事实显然并非如此。下面的 foreach 循环可以工作:

for (MovieEntry title : Database) {
    System.out.println(title);
}

请考虑遵循在字段中使用小写名称的约定，即调用您的 ArrayList<MovieEntry>名称如 database而不是Database .