单例模式。
第一种形式:
public class Singleton {
private Singleton(){}
private static Singleton instance = new Singleton();
public static Singleton getInstance(){
return instance;
}
}
第二种形式:
public class Singleton {
private static Singleton instance = null;
public static synchronized Singleton getInstance(){
if (instance==null)
instance＝new Singleton();
return instance;
}