成都网站建设公司哪家好一些？

 您必须先在某处初始化ArrayList实例，然后才能像这样实际添加值 
 
public ArrayList<TextView> Durations = new ArrayList<TextView>();
public ArrayList<Long> periods = new ArrayList<Long>();
 
 直接来自文档， 
 
 什么时候抛出NullPointerException？ 
 
 
 
 当应用程序在需要对象的情况下尝试使用null时抛出。 这些包括： 
 
 
 
 
 调用null对象的实例方法。 
 
 
 访问或修改空对象的字段。 将null的长度视为数组。 
 
 
 访问或修改null的插槽，就像它是一个数组一样。 
 
 
 抛出null，好像它是一个Throwable值。 
 

You have to initialize the ArrayList instances somewhere before you can actually add values to it like this
 
public ArrayList<TextView> Durations = new ArrayList<TextView>();
public ArrayList<Long> periods = new ArrayList<Long>();
 
Directly from the documentation,
 
When NullPointerException is thrown?
 
 
 
Thrown when an application attempts to use null in a case where an object is required. These include:
 
 
 
 
Calling the instance method of a null object.
 
 
Accessing or modifying the field of a null object. Taking the length of null as if it were an array.
 
 
Accessing or modifying the slots of null as if it were an array.
 
 
Throwing null as if it were a Throwable value.