Java利用ArrayList通过GUI将联系人（对象）写入和读取到文件

Question

I'm writing a pretty simple program GUI program that emulates a cell phone. The "cell phone" has four main buttons: phone, contacts, message, and apps. I've coded all the GUI and hit a snag while working on the Contact class, which is the backbone of the entire program!

The Contact class is very straightforward, it has two instance variables of type String which are 'name' and 'number'. I want to build an ArrayList of type Contact, allow for contacts to be added, and then create methods to append to and read in from a serialized file.

At this point I'm very stuck on how to create methods to add objects to the arrayList, and then create methods to append to and read in from a serialized file.

Here is the Contact class:

public class Contact
{
    public String name, number;

Contact()
{}

Contact (String theName, String theNumber)
{
    this.name = theName;
    this.number = theNumber;
}

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

public void setNumber(String aNumber)
{
    this.number =aNumber;
}

public String getName()
{
    return name;
}

public String getNumber()
{
    return number;
}

public String toString()
{
    return name + ": " + number;
}

public boolean equals(Contact other)
{
   if (name.equals(other.getName())  && number.equals(other.getNumber()))
   {
      return( true );
   }
   else
   {
      return( false );
   }
}
}

Thanks for the quick responses. I've corrected the equals method and moved the ArrayList to it's own class. I also cleared up the error on the read method (Java 7 issue). The current issue I'm running into is on these lines:

out.writeObject(contact);

and

Contact contact = (Contact)in.readObject();

Since I'm trying to write to and read from an ArrayList, shouldn't the methods reflect that?

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

class ContactsCollection implements Serializable
{
    public static final long serialVersionUID = 42L;

ArrayList <Contact> contactList = new ArrayList<Contact>();

public void write()
{
    try 
    {
        ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("contactList.dat"));
        out.writeObject(contact);
    } 
    catch(IOException e)
    {
        e.printStackTrace();
    }
}

public void read()
{
    try
    {
         ObjectInputStream in = new ObjectInputStream(new FileInputStream("contactList.dat"));
         Contact contact = (Contact)in.readObject();
    } 
    catch (IOException e)
    {
        e.printStackTrace();
    }
    catch (ClassNotFoundException e)
    {
        e.printStackTrace();
    }
}
}

Answer 1

Appending to the list is as easy as list.add(contact) .

Writing to serialization:

try {
    ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(file));
    out.writeObject(contact);
} catch(IOException e) {
    e.printStackTrace();
}

Reading:

try {
    ObjectInputStream in = new ObjectInputStream(new FileInputStream(file));
    Contact contact = (Contact)in.readObject();
} catch(IOException | ClassNotFoundException e ) {
    e.printStackTrace();
}

Answer 2

I am afraid that I really understand what you are trying to achieve but I can see two problems in your code:

1. You have created your Contact class with static attributes, which means all the objects will share the same value of name & number. It seems to be problematic and i will advice you to create non-static attributes when there seems to be no need to share them.

public static String name, number;

Second problem in your class is that you have put the arraylist of contacts also in it. And you have made the class seriablizable. It means everytime you serialize your contact object, your arraylist will also be serialized along with it, which i assume is not desired. You should create another class and name it such as ContactsCollection and simply create a Arraylist in it, you may chose to have a static arraylist here.

In your GUI, if you are creating and object, then create an instance of Contact. And then simply add it your ContactsCollection.contactList(). You may add methods to serialize also in your ContactsColleciton class. You may chose to have a single method in ContactsCollection with argument as Contact object. First you add the object in the list and then serialize it.

Answer 3

It would be too long to post as a comment, hence I post this as an answer.Apart from the already answered points, I want to add a few of my observations here.

There are certain mistakes(if they are unintended) in your code:

You are declaring name and number both as static . What it does is that all the instances of your class Contact will share the same name and number . I presume all the contacts having same name and number is something very unheard and unintended.

public static String name, number;

So correct it to

public String name, number;

Though it's more of a warning, but you should provide a serialVersionUID to your Serializable class . The serialization runtime associates with each serializable class a version number, called a serialVersionUID, which is used during deserialization to verify that the sender and receiver of a serialized object have loaded .

public static final long serialVersionUID = 42L;

Your definition of equals() will create issues.You are using == to check the equality of two String which in turn will only check for equal references. Better approach would be to use the overridden equals() of String which compares the contents.

if (name.equals(other.getName())  && number.equals(other.getNumber()))
{
    return true;
}
else
{
   return false;
}

Once you override the equals() for the Contact class, override its hashCode() as well.