单例模式

为了防止通过反序列化得到多个对象，EJ提倡使用enum实现单例：

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
public class Test {
	public static void main(String[] args) throws Exception {
		Singleton d1 = Singleton.INSTANCE;
		d1.setName("a fucker.");
		System.out.println(d1);
		
		FileOutputStream fos = new FileOutputStream("out.data");
		ObjectOutputStream oos = new ObjectOutputStream(fos);
		oos.writeObject(d1);
		fos.close();
		oos.close();
		
		FileInputStream fis = new FileInputStream("out.data");
		ObjectInputStream ois = new ObjectInputStream(fis);
		Object o = ois.readObject();
		fis.close();
		ois.close();
		
		Singleton d2 = (Singleton)o;
		
		System.out.println(d2);
		System.out.println(d1 == d2);
	}
}
enum Singleton implements Serializable {
	
	INSTANCE;
	
	private String name;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	@Override
	public String toString() {
		return "[" + name + "]";
	}
}

比较全的单例分析文章：
http://www.blogjava.net/kenzhh/archive/2013/03/15/357824.html