java - 在Java中尝试异常，try/catch block 和单例

Question

我正在尝试学习在Java中处理错误/抛出异常。
我有一个类UserDatabase，它保存着一个学生集合，它也应该将集合保存到文件中。

我相当确定自己做得不好的是文件处理方法。方法public boolean saveDatabase不应引发异常，并且应在try-catch中进行处理，并应使用Student类中Student对象上的student类的encode方法将每个对象写为文件中的一行。这是正在编译，但在我看来。在书中说写方法public boolean saveDatabase();如您所见，我更改了标题以使其对我有意义。这主要是因为我不知道如何编写以()结尾的 header 的方法；

方法public boolean loadDatabase也应该处理可能的IO错误，如果发生错误则返回false。对于该字段中的每一行，它应该由sudent类的构造函数public Student(String encodingStudent)创建一个学生对象。如果无法将文件中的一行解码为学生，则应抛出新的异常DatabaseFormatException(这是一个单独的类)。这个也被列为public boolean loadDatabase();在书里。面对现实吧，这个完全关闭了。我不知道该怎么办，而且我已经花了好几个小时不停地工作，看书，上网阅读，我迷路了。

这是我的代码:

   /**
* This method should not throw exceptions.
* By using a try/catch block, we anticipate possible failures.
* We recognize that these actions might fail and throw errors.
*/
   public boolean saveDatabase() throws IOException {
   //This method is using the encode method on student objects and should
   //write each object as a line in the file. 
   String encode = null;
   boolean saved;
   try {

       encode = null;
   userdatabase.saveDatabase();
   saved = false;
}
   catch (IOException e) {
       System.out.println("Error");
       saved = false;
    }
    finally {
        if(encode.equals(students)) {
        //System.out.println("Students" + students)?;
        saved = true;
    }
    } 
   return saved;
}

   /**
    * Method loadDatabase should handle possible IO errors, and return false
    * if one occurs. Otherwise, it should return true and create a new 
Student object
    * by using the constructor public Student(String encodedStudent).
    * If a line cannot be decoded as a student, the method should throw a 
new
    * exception "DatabaseFormatException".
    * 
    */
     public boolean loadDatabase() throws IOException,DatabaseFormatException {
   //Attempting to use the String encodedStudent constructor from Student class
   String encodedStudent = null;
   boolean loaded;
   try {
       //Attempting to create possible IO errors returning false if they occur
       enco dedStudent = null;
       //UserDatabase.loadDatabase(encodedStudent);
       loaded = false;
    }
    catch(IOException e) {
        if (encodedStudent == null) {
            System.out.println("Error");
            loaded = false;
        }
    }
    //Trying a for each loop to throw a DatabaseFormatException

   for(Student student : students) {
        //This is supposed to throw a DatabaseFormatException if a 
        //line in the file cannot be decoded as a student!
       if(student.getName.isEmpty() && this.course.isEmpty()) {
            throw new DatabaseFormatException(
            "No student found");
        }
    }

Answer 1

您的代码应为

public boolean saveDatabase() {
   try {
        // maybe do some more work...
        userdatabase.saveDatabase();
        return true;
    } catch (IOException e) {
        return false;
    }
}

只需根据是否发生异常返回 true/false。删除 saved，因为您不再需要它。删除 encode，因为您一开始就不需要它，也从未为其分配值。