用二进制文件读写和保存序列化对象

Question

I am working on a project in which I want the user to be able to input Objects into an ArrayList, close the program, and be able to open the program again and have the previous ArrayList (from the first run) accessible to the user.

I currently have the user input objects into an ArrayList, the list serializes and saves the ArrayList as a .bin file. When I run the program again, the previous list is saved but when I enter new values, it overrides the old list. I guess what I am looking for is a way to see if my .bin file exists, and if it does, add new objects to the ArrayList, and if it doesn't, create a new one. I'll add some sample code below.

Here I create the arraylist and a string for which the .bin file is created.

public class Tender {
ArrayList<Alcohol> arraylist = new ArrayList<Alcohol>();
String dataList = "dataList.bin";
}

Here is where I serialize the ArrayList.

    private void Serialize() throws IOException {
         try (ObjectOutputStream os = new ObjectOutputStream(new  FileOutputStream(dataList))) {
             os.writeObject(arraylist);
             os.close();

             System.out.println("done writing");
         }
     }

And here is where I try to load back the serialized file from the previous run.

private void load() throws FileNotFoundException, IOException, ClassNotFoundException {
    try (ObjectInputStream is = new ObjectInputStream(new FileInputStream(dataList))) {
        ArrayList newAL;
        newAL = (ArrayList) is.readObject();
        System.out.println(newAL);
    }
    Start();
}
}

Answer 1

The way to see if the file exists is to try to open it, and catch the FileNotFoundEzception that occurs if it isn't there. If it's there, read the list; if it isn't, create a new one.