Question

长时间阅读，第一次查询。我对java很新，我有一个问题，特别是使用比较器来比较我保存为链接哈希映射的yaml文件中的日期。在尝试使用比较器对我的yaml文件中的日期进行排序后，我收到了ClassCastException：LinkedHashMap无法强制转换为约会

以下是代码：

import org.yaml.snakeyaml.*;


public class DaysheetGenerator {
    public static void main(String[] args) throws Exception {
        //Creates a string with the file name
        String fileName = "resources/daysheet.yml";

        //Creates a new yaml daysheet 
        Yaml daysheet = new Yaml();

        // new instance of reader for YAML file
        Reader reader = null;

        try {
            // pass yaml file into the reader to create a new instance of     the YAML file for output
            reader = new FileReader(fileName);

            Map<String, List<Appointment>> lhm = new LinkedHashMap<>();

            // casted a as Map during load, saved to variable lhm
            lhm = (Map<String, List<Appointment>>)daysheet.load(reader);

            // get the value based on the key, "appointments"
            List<Appointment> list = lhm.get("appointments");

            // sort the list of appointments by date
            Collections.sort(list, new Comparator<Appointment>() {

                @Override
                public int compare(Appointment a1, Appointment a2) {                    
                    return a1.getDate().compareTo(a2.getDate());
                }

            });


            // print list
            System.out.println(list);

        }
        // if file cannot be found, print exception
        catch (FileNotFoundException e) {
            System.out.println("Could not find yaml file " + e);

            e.printStackTrace();
        }
        finally 
        {
            // close the reader after trying to read the file as long as the file exists
            if (null != reader) {
                try {
                    reader.close();
                } catch(final IOException ioe) {
                    System.err.println("Recieved exception when trying to close reader" + ioe);
                }
            }
        }

    }
}

感谢任何帮助。再次感谢！

PS：我使用Snakeyaml，如果这有任何区别

Answer 1

lhm = (Map<String, List<Appointment>>)daysheet.load(reader);

这应该是有问题的陈述。在这里，我认为比较器没有错。 daysheet.load(reader)没有给你一个链接的hashmap，你试图在LinkedHashMap

中投射它

ClassCastException：LinkedHashMap无法使用Java中的Comparator强制转换为自定义对象

1 个答案: