大家好，由於小弟最近才剛java懇請各位專家幫幫忙，我在寫一個進銷貨系統，主要是有一個叫做Cproduct的class還有extends的Cthing類別，建立一個物件陣列class Cproduct[]=new Cproduct[100];然後我把這個物件陣列利用objectoutputstream存到外部的txt檔，現在想要把這個物件陣列從外部txt檔讀入，並存入陣列要怎麼作??因為這個陣列有存入父類別class還有他extends的子類別class。。。
以下是程式碼(有錯!):
public class JavaApplication16 {

/**
 * @param args the command line arguments
 */
public static void main(String[] args) throws IOException, ClassNotFoundException {
    Scanner sc = new Scanner(System.in);
    Cproduct obj[] = new Cproduct[100];
    int choise, i = 0;
    int item[] = new int[100];
    String tempstr;
    int tempid, tempnum;
    for (i = 0; i < 100; i++) {
        System.out.print("1.商品1 2.商品2 3.離開:");
        choise = sc.nextInt();
        if (choise == 1) {
            System.out.print("name:");
            item[i] = 1;
            tempstr = sc.next();
            System.out.print("id:");
            tempid = sc.nextInt();
            obj[i] = new Cproduct(tempstr, tempid);
        }
        if (choise == 2) {
            System.out.print("name:");
            item[i] = 2;
            tempstr = sc.next();
            System.out.print("id:");
            tempid = sc.nextInt();
            System.out.print("num:");
            tempnum = sc.nextInt();
            obj[i] = new Cthing(tempstr, tempid, tempnum);
        }
        if (choise == 3) {
            break;
        }
    }
    System.out.println("success!");
    Cproduct.show(obj, item, i);
    FileOutputStream fo
            = new FileOutputStream("C:\\Users\\USER\\Desktop\\2266.txt");
    ObjectOutputStream oos = new ObjectOutputStream(fo);
    for (int a = 0; a < obj.length; a++) {
        if (item[a] == 1) {
            oos.writeObject(new Cproduct(obj[a].name, obj[a].id));
        }
        if (item[a] == 2) {
            oos.writeObject(new Cthing(obj[a].name, obj[a].id, ((Cthing) obj[a]).num));
        }
    }
    oos.close();
    fo.close();
    obj = null;
    FileInputStream fi
            = new FileInputStream("C:\\Users\\USER\\Desktop\\2266.txt");
    ObjectInputStream ois = new ObjectInputStream(fi);
    obj = (Cproduct[]) ois.readObject();
    for (int a = 0; a < obj.length; a++) {
        if (obj[a].getClass().isAssignableFrom(Cproduct.class)) {
            System.out.println("obj" + a + ":" + obj[a]);
        } else if (obj[a].getClass().isAssignableFrom(Cthing.class)) {
            System.out.println("obj" + a + ":" + (Cthing) obj[a]);
        }
    }
    ois.close();
    fi.close();
}

}

class Cproduct implements Serializable {

public String name;
public int id;

public Cproduct() {
}

public Cproduct(String a, int b) {
    name = a;
    id = b;
}

public static void show(Cproduct arr[], int item[], int i) {
    for (int a = 0; a < i; a++) {
        if (item[a] == 1) {
            System.out.println("第一類");
            System.out.println("\t" + "name:" + arr[a].name);
            System.out.println("\t" + "id:" + arr[a].id);
        }
        if (item[a] == 2) {
            System.out.println("第二類");
            System.out.println("\t" + "name:" + arr[a].name);
            System.out.println("\t" + "id:" + arr[a].id);
            System.out.println("\t" + "num:" + ((Cthing) arr[a]).num);
        }
    }
}

public String toString() {
    return (name + "," + id);
}

}

class Cthing extends Cproduct {

public int num;

public Cthing() {
}

public Cthing(String a, int b, int c) {
    super(a, b);
    num = c;
}

public static void show(Cproduct arr[], int i) {
    System.out.println("2");
    System.out.println("name:" + arr[i].name);
    System.out.println("id:" + arr[i].id);
    System.out.println("id:" + ((Cthing) arr[i]).num);
}

public String toString() {
    return (name + "," + id + "," + num);
}

}