1.饿汉式：
public class SingleTon {
private SingleTon(){
}
private final static SingleTon instance = new SingleTon();
public static SingleTon getInstance(){
return instance;
}
}
2.懒汉式：
public class SingleTon {
private SingleTon(){
}
private static SingleTon instance = null;
public static synchronized SingleTon getInstance(){
if(instance == null)
instance = new SingleTon();
return instance;
}
}
3.枚举：
public enum SingleTon {
instance;
}