java - 将 ArrayList 从对象更改为更具体的类型

Question

是否可以更改数组列表的对象类型，即从对象 ArrayList 更改为特定对象 ArrayList。我尝试过对每个使用 a 。或者，是否有一种方法可以更改文件处理方法，以便它可以根据读取的文件返回特定类型，而无需重复代码？

我的尝试:

ArrayList<Object> librarianList = FileHandling.getLibrarianRecords(fileName);
ArrayList<Librarian> libList = new ArrayList<>();
for (Object addType: librarianList) {
libList.add(addType);
}

获取LibrarianRecords代码

public static ArrayList<Object> getLibrarianRecords(String filename){
                ArrayList<Object> fromFile = new ArrayList<>(); //Array of
                // existing librarians

                try{
                        FileInputStream fIS =
                                new FileInputStream(SYSTEM_PATH + filename);
                        ObjectInputStream oIS = new ObjectInputStream(fIS);
                        fromFile = (ArrayList<Object>)oIS.readObject();
                } catch (IOException ex){
                        System.out.println("Failed to read from file " + ex.getMessage());
                        ex.printStackTrace(); //Catches an IO exception.
                } catch (ClassNotFoundException ex){
                        System.out.println("Error class not found" + ex.getMessage());
                        ex.printStackTrace(); //Catches a class not found
                        // exception.
                }

                return fromFile; //Returns the array list.
        }

Answer 1

从这样的文件中读取对象并不是一个好主意。也就是说，您真正需要做的就是转换 oIS.readObject() 的结果。到ArrayList<Librarian>而不是将其携带到 ArrayList<Object> (就像你现在所做的那样)然后修改 getLibrarianRecords 的返回类型。哦，当然还有局部变量 fromFile 的类型.

    public static ArrayList<Librarian> getLibrarianRecords(String filename){
            ArrayList<Librarian> fromFile = new ArrayList<>(); //Array of
            // existing librarians

            try{
                    FileInputStream fIS =
                            new FileInputStream(SYSTEM_PATH + filename);
                    ObjectInputStream oIS = new ObjectInputStream(fIS);
                    fromFile = (ArrayList<Librarian>)oIS.readObject();
            } catch (IOException ex){
                    System.out.println("Failed to read from file " + ex.getMessage());
                    ex.printStackTrace(); //Catches an IO exception.
            } catch (ClassNotFoundException ex){
                    System.out.println("Error class not found" + ex.getMessage());
                    ex.printStackTrace(); //Catches a class not found
                    // exception.
            }

            return fromFile; //Returns the array list.
    }

这样就不需要循环列表来实际逐个元素地进行类型转换。