向列表添加元素时出现空指针异常

Question

我在向列表中添加元素时遇到 nut 指针异常。错误是 System.NullPointerException：尝试取消引用 out.add(Time.newInstance(17,00,00,00));

上的空对象

public class BusScheduleCache 
{   //Variable
private Cache.OrgPartition part;

//Constructor 
public BusScheduleCache()
{
    Cache.OrgPartition newobj = Cache.Org.getPartition('local.BusSchedule');
    part = newobj;
}

//methods
public void putSchedule(String busLine, Time[] schedule)
{
    part.put(busline, schedule);
}

public Time[] getSchedule (String busline)
{
    Time[] out = new List<Time>();

    out = (Time[]) part.get(busline);
    if (out == null)
    {
        out.add(Time.newInstance(8, 00, 00, 00));
        out.add(Time.newInstance(17,00,00,00));

    }

        return out;

}

}

Answer 1

问题是您正在检查列表 out 是否为 null:

if (out == null) { }

在该条件下，您将添加到 null 列表。

还要查看这两行：

Time[] out = new List<Time>();

out = (Time[]) part.get(busline);

首先用一个新列表实例化变量 out，然后再次为它分配 null 引用。

做这样的事情可能会有用：

Time[] out = part.containsKey(busline) ? 
                     (Time[]) part.get(busline) : new List<Time>();
if (out.isEmpty())
{
    out.add(Time.newInstance(8, 00, 00, 00));
    out.add(Time.newInstance(17,00,00,00));
}

return out;

向列表添加元素时出现空指针异常

null pointer exception in adding element to list

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