Externalizable的使用方法

package com.itbuluoge.object;

import java.io.Externalizable;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectInputStream;
import java.io.ObjectOutput;
import java.io.ObjectOutputStream;

 class Moon implements Externalizable{

	public Moon()
	{
		System.out.println("moon");
	}
	public void readExternal(ObjectInput arg0) throws IOException,
			ClassNotFoundException {
		// TODO Auto-generated method stub
		System.out.println("reading moon!");
	}

	public void writeExternal(ObjectOutput arg0) throws IOException {
		// TODO Auto-generated method stub
		System.out.println("writing moon!");
	}

}
class Sun implements Externalizable
{
	Sun()
	{
		System.out.println("sun");
	}
	public void readExternal(ObjectInput in) throws IOException,
			ClassNotFoundException {
		// TODO Auto-generated method stub

	}

	public void writeExternal(ObjectOutput out) throws IOException {
		// TODO Auto-generated method stub

	}

}

public class Stars
{
	public static void main(String[] args) throws Exception, IOException
	{
		Moon moon=new Moon();
		Sun sun=new Sun();

		ObjectOutputStream o=new ObjectOutputStream(new FileOutputStream("star.out"));
		o.writeObject(moon);
		o.writeObject(sun);
		o.close();

		ObjectInputStream in=new ObjectInputStream(new FileInputStream("star.out"));
		moon=(Moon)in.readObject();
		sun=(Sun)in.readObject();
		in.close();

	}
}

我们能够看到输出结果

我们对moon的写和读序列化都没有问题，可是对sun的写没有问题，可是在读出的时候。抛出异常，由于实现了Externalizable接口的类，会调用构造函数，而sun的构造函数是私有的。无法訪问，从而导致抛出异常。