java - 找不到符号 - 方法添加

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这个问题已经有答案了:

What does a "Cannot find symbol" or "Cannot resolve symbol" error mean? (18 个回答)

已关闭 2 年前。

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)我收到的错误是“找不到符号 - 方法添加”，但我在顶部声明了一个 ArrayList。这是我的全部代码，我知道还有其他错误。

**public class MovieDatabase
{
   public ArrayList<String> Database = new ArrayList<String>();

   public MovieDatabase(){
       ArrayList<String> Database = new ArrayList<String>(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);
    }

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

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

   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>();

    }

}**

我还有一个错误，指出方法 getYear() 无法找到，即使它位于另一个类中，它不是静态的，并且我正在创建一个调用另一个类的对象 (MovieEntry m)。

编辑:我的 searchTitle 方法仍然收到错误，提示数据库类型不兼容。有人可以解释我的 for-each 循环的问题吗？我尽我所能地阅读了这本书。不过，感谢您迄今为止的所有帮助!

Answer 1

你的构造函数定义了一个局部变量Database隐藏类变量。正确的是:

public MovieDatabase(){
    Database = new ArrayList<String>(0);
}

主要问题是当你调用Database.add(m);时您要添加 MovieEntry实例到ArrayList<String>仅支持添加字符串。

public class MovieDatabase
{
   public ArrayList<MovieDatabase> database = new ArrayList<MovieDatabase>();

   public MovieDatabase(){
   }

   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);
    }