单例模式的作用就是保证只有一个实例化对象；例如Calender类 全世界只有一个时间
class Singlton{
private static Singlton singlton=new Singlton();
private Singlton(){}
public static Singlton getInstance(){
return singlton;
}
public void method(){System.out.println("其他方法“);}
}
public class App{
public static void main(String[] args){
Calendar calendar = Calendar.getInstance();
Singlton sing = Singlton.getInstance();
singlton.method();
}
}