externalizabledemo.java

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// 例5.5.8 ExternalizableDemo.java
import java.io.*;
class ExternalizableDemo implements Externalizable
{
	// 声明两个变量
	int i;
	String s;
	public ExternalizableDemo()//定义ExternalizableDemo类的无参构造函数
	{
		System.out.println("ExternalizableDemo's Constructor");
	}
//  定义ExternalizableDemo类的带参构造函数，用来初始化
	public ExternalizableDemo(String s, int i) 
	{
		System.out.println("ExternalizableDemo(String s, int i)");
		this.s = s;
		this.i = i;
	}
	public String toString() { return s + i; }

	// 在序列化时自动调用，可以用来指定序列化哪些内容
	public void writeExternal(ObjectOutput out) throws IOException
	{
		System.out.println("ExternalizableDemo.writeExternal()");
		out.writeObject(s);  // 将字符串对象写入对象流
		out.writeInt(i);  // 将整型变量写入对象流
	}
    // 在反序列化时自动调用，可以用来指定反序列化哪些内容
	public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException
	{
		System.out.println("ExternalizableDemo.readExternal()");
		s = (String)in.readObject();  // 将字符串对象从对象流中恢复
		i =in.readInt();   // 将整型变量从对象流中恢复
	}
	public static void main(String[] args)
	{
		System.out.println("Constructing objects:");
		ExternalizableDemo ed = new ExternalizableDemo("String ", 50);
		System.out.println(ed.toString());
		try 
		{
			ObjectOutputStream out = new ObjectOutputStream(
				new FileOutputStream("data.ext"));
			System.out.println("Saving object:");
			out.writeObject(ed);
			out.close();

			ObjectInputStream in = new ObjectInputStream(
				new FileInputStream("data.ext"));
			System.out.println("Recovering from data.ext:");
			ed = (ExternalizableDemo)in.readObject();
			System.out.println(ed.toString());
		} catch(Exception e) {
			e.printStackTrace();
		}
	}
}