未序列化的Arraylist总是空的

Question

我在Java中有很多类,但这是我第一次尝试序列化任何东西.我创建了自己的课程,其中包括一个arraylist.主要对象是这些类的arraylist.我相信我已经做好了一切,但是当我再读回来时,arraylist总是空着的.

主要(主要是测试)类:

import java.io.*;
import java.util.ArrayList;

public class IOTest {
public static void main(String[] args) {
    ArrayList<Info> master = new ArrayList <Info>();
    Info a = new Info("a");
    Info b = new Info("a");
    Info c = new Info("a");
    master.add(a);
    master.add(b);
    master.add(c);
    print(master);
    save(master);
    ArrayList<Info> loaded = new ArrayList <Info>();
    load(loaded);
    System.out.println("Loaded List:");
    System.out.println("Loaded Size:" + loaded.size());
    print(loaded);
}

public static void save(ArrayList a){
    File f = new File("savefile.dat");
    try {
        FileOutputStream fos = new FileOutputStream(f);
        ObjectOutputStream oos = new ObjectOutputStream(fos);
        oos.writeObject(a);
        fos.flush();
        fos.close();
     } catch (IOException ioe) {
         System.out.println("Failed to save");
     };
}

public static void load(ArrayList a){
    File f = new File("savefile.dat");
    try {
        FileInputStream fis = new FileInputStream(f);
        ObjectInputStream ois = new ObjectInputStream(fis);
        try {
          a = (ArrayList<Info>) ois.readObject();
        } catch (ClassNotFoundException cnfe) { 
            System.out.println("Failed to load");
        }
        fis.close();
     } catch (IOException ioe) {
         System.out.println("Failed to load");
     }
}

public static void print(ArrayList a){
    System.out.println(a);
}
}

自定义数据结构:

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.ArrayList;


public class Info implements Serializable {
private static final long serialVersionUID = -5781559849007353596L;

ArrayList<String> list;
public Info( String e) {
    list = new ArrayList<String>();
    list.add(e);
}
@Override
public String toString() {
    return list.toString();
}

private void readObject(ObjectInputStream aInputStream) throws ClassNotFoundException, IOException {
    aInputStream.defaultReadObject();
}

private void writeObject(ObjectOutputStream aOutputStream) throws IOException {
    aOutputStream.defaultWriteObject();
}
}

如果有人能够指出我做错了什么,我将非常感激.

Answer 1

此问题与序列化无关.

您正在更改方法reference of passed parameter内的列表,load()这将无法工作,因为更改的引用将只有范围,直到该方法.将负载更改为以下

public static ArrayList<Info> load() {//Change return type
    File f = new File("savefile.dat");
    try {
        FileInputStream fis = new FileInputStream(f);
        ObjectInputStream ois = new ObjectInputStream(fis);
        try {
            ArrayList<Info> a = (ArrayList<Info>) ois.readObject();//get the object that is read
            return a;
        } catch (ClassNotFoundException cnfe) {
            System.out.println("Failed to load");
        }
        fis.close();
    } catch (IOException ioe) {
        System.out.println("Failed to load");
    }
    return null;
  }

并使用返回的对象.

 ArrayList<Info> loaded = load();