Question

我有一个我正在研究的项目，而且我需要创建一个抽象类AbstractCustomer的ArrayList; ArrayList需要由从数据或文本文件读入的AbstractCustomer组成，所以我试图通过数据文件来完成但不能绕过它？

这是我的班级：

import java.io.FileOutputStream;
import java.io.*;

public abstract class AbstractCustomer implements Serializable {

    private static final long serialVersionUID = 1L;
    private String name;
    private String phoneNumber;
    private final int MIN_LENGTH = 10;

    public AbstractCustomer() {

    }

    public AbstractCustomer(String name, String phoneNumber) {
        this.name = name;
        this.phoneNumber = phoneNumber;

        //Phone number is less than 10, but what if it's more than 10?
        //Assignment doesn't say, so I will assume it can be more than 10.
        //Ya know country codes 1845 and all that
        if (phoneNumber.length() < MIN_LENGTH) {
            throw new NumberFormatException("Phone number must be at least 10 digits long.");
        }

        //Parse the long, so this will rule out anything else except digit.
        try {
            Long.parseLong(phoneNumber);
        } catch (NumberFormatException e) {
            System.out.println("Phone number can only contain digits, please no dashes ('-') or spaces (' ')");
        }

    }

    abstract double returnDiscountPrice(double itemCost);

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPhoneNumber() {
        return phoneNumber;
    }

    public void setPhoneNumber(String phoneNumber) {
        this.phoneNumber = phoneNumber;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        AbstractCustomer other = (AbstractCustomer) obj;
        if (name == null) {
            if (other.name != null)
                return false;
        } else if (!name.equals(other.name))
            return false;
        if (phoneNumber == null) {
            if (other.phoneNumber != null)
                return false;
        } else if (!phoneNumber.equals(other.phoneNumber))
            return false;
        return true;
    }

    @Override
    public String toString() {
        return "AbstractCustomer[name=" + name + ", phoneNumber=" + phoneNumber + "]";
    }


}

这就是我想要做的事情：

public void createDataFile() {
    try {
        FileOutputStream fout = new FileOutputStream("C:\\Users\\Frank\\Desktop\\Assignment\\abstract.dat");
        ObjectOutputStream outputStream = new ObjectOutputStream(fout);
        outputStream.writeObject(HOW DO I WRITE THE ABSTRACT CLASS TO A FILE HERE????);
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

} 任何帮助表示赞赏！

Answer 1

首先，使用IO编写的是一个对象，而不是一个类。您可以在oracle documentation中阅读：

抽象类无法实例化，但它们可以是子类。

您需要做的是删除抽象标识符（我没有看到任何抽象方法）或继承此抽象类。

只有这样，您才能实例化类的对象（Not）AbstractCustomer并使用IO对它们进行序列化。

您的抽象类是Serializable的唯一原因是扩展It的类也可以序列化。我希望这很清楚。

这是一个序列化的例子：（请注意，我创建了一个继承抽象类的嵌套类。不要这样写。我只是为了演示目的而做的。主方法不适用于那个案例）：

// this cannot be serialized because no objects can be instantiated
public abstract class SerializationTest {

// this can be, because it's not abstract
public static class SerializationTestB extends SerializationTest {

        public static void main(String[] args) {

        // instantiation of an object that you want to write to file
        SomeObject obj = new SomeObject(param, param, param);
        SomeObject obj2 = new SomeObject(param, param, param);
        SomeObject obj3 = new SomeObject(param, param, param);
        SomeObject obj4 = new SomeObject(param, param, param);
        SomeObject obj5 = new SomeObject(param, param, param);
        SomeObject obj6 = new SomeObject(param, param, param);

        // an object that represents the path of the file
        File f = new File("some/path/here");

        ObjectOutputStream out = new ObjectOutputStream(new BufferedOutputStream(new FileOutputStream(f))); 
        out.writeObject(obj);
        out.writeObject(obj2);
        out.writeObject(obj3);
        out.writeObject(obj4);
        out.writeObject(obj5);
        out.writeObject(obj6);

        out.flush();
        out.close();
    }
}

}

FileList中的ArrayList（抽象类）

1 个答案: