Java 无法添加到我的列表，引发NullPointerException

我想我想做的事情相当简单，但我来自PHP背景（你知道，大部分繁重的工作都是为你完成的）

基本上，我的日志如下：

12-06 15:45:18.282: D/MAPVIEW(32047): Matching Providers are: [network, gps]
12-06 15:45:18.282: D/MAPVIEW(32047): Um, whats the best provder? Well its obviously 'network'
12-06 15:45:18.753: D/MAPVIEW(32047): Location Data: Lat:49, Long: -116
12-06 15:45:18.753: D/MAPVIEW(32047): Could not add coordinate array to List, Error: java.lang.NullPointerException
12-06 15:45:18.753: D/MAPVIEW(32047): Location Data: Lat:50, Long: -116
12-06 15:45:18.753: D/MAPVIEW(32047): Could not add coordinate array to List, Error: java.lang.NullPointerException
12-06 15:45:18.753: D/MAPVIEW(32047): Location Data: Lat:49, Long: -117
12-06 15:45:18.753: D/MAPVIEW(32047): Could not add coordinate array to List, Error: java.lang.NullPointerException
12-06 15:45:18.753: D/MAPVIEW(32047): Location Data: Lat:49, Long: -115
12-06 15:45:18.753: D/MAPVIEW(32047): Could not add coordinate array to List, Error: java.lang.NullPointerException
12-06 15:45:18.753: D/MAPVIEW(32047): Location Data: Lat:49, Long: -117
12-06 15:45:18.753: D/MAPVIEW(32047): Could not add coordinate array to List, Error: java.lang.NullPointerException
12-06 15:45:18.753: D/MAPVIEW(32047): Location Data: Lat:49, Long: -117
12-06 15:45:18.763: D/MAPVIEW(32047): Could not add coordinate array to List, Error: java.lang.NullPointerException
12-06 15:45:18.763: D/MAPVIEW(32047): Location Data: Lat:50, Long: -115
12-06 15:45:18.763: D/MAPVIEW(32047): Could not add coordinate array to List, Error: java.lang.NullPointerException
12-06 15:45:18.763: D/MAPVIEW(32047): Location Data: Lat:49, Long: -116
12-06 15:45:18.763: D/MAPVIEW(32047): Could not add coordinate array to List, Error: java.lang.NullPointerException
12-06 15:45:18.763: D/MAPVIEW(32047): Location Data: Lat:50, Long: -118
12-06 15:45:18.763: D/MAPVIEW(32047): Could not add coordinate array to List, Error: java.lang.NullPointerException
12-06 15:45:18.763: D/MAPVIEW(32047): Location Data: Lat:49, Long: -114
12-06 15:45:18.783: D/MAPVIEW(32047): Could not add coordinate array to List, Error: java.lang.NullPointerException
12-06 15:45:18.783: D/AndroidRuntime(32047): Shutting down VM
12-06 15:45:18.783: W/dalvikvm(32047): threadid=1: thread exiting with uncaught exception (group=0x4001d5a0)

您将看到我正在尝试添加到坐标列表中，而try-catch正在捕获异常。 （暂时不要担心撞车，我会处理的。）

因此，没有更多的adeu，以下是我的相关代码：

package com.private.clientndablocked;

// ... imports

public class ShowMapView extends MapActivity {

    // ... some initializers
    List<int[]> allLocations;


    @Override
    protected boolean isRouteDisplayed() {
        return false;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // .. whole bunch of other unreleated stuff



        // A single json object, this gets populated with cherry picked json array items
        JSONObject obj = null;

        // go through each of the items in the json array
        for(int i = 0; i < json.length(); i++) {

            try {
                // We must try to get the object first
                obj = (JSONObject) json.get(i);
            } catch (JSONException e) {

                e.printStackTrace();
            }

            // Initialize temp data with defaults
            int Latitude = 0;
            int Longitude = 0;
            String Title = "";
            String ID = "";
            int[] coords = new int[2];

            // So we actually have a picked item?
            if(obj != null)
                try {

                    // Lets try to assign the temp vars with their real data
                    Latitude = (int) (obj.getDouble("lat") * 1e6);
                    Longitude = (int) (obj.getDouble("long") * 1e6);
                    Title = (String) (obj.getString("title"));
                    ID = (String) (obj.getString("id"));


                    // Save the lat and long of the new location data (non micro) 
                    // This stuff goes into allLocations List
                    coords[0] = obj.getInt("lat");
                    coords[1] = obj.getInt("long");

                } catch (JSONException e) {
                    e.printStackTrace();
                }

            // Create a new GeoPoint to store the microdegrees into
            GeoPoint point = new GeoPoint(
                Latitude, 
                Longitude
            );

            // Create a new OverlayItem with the GeoPoint and a title and snippet
            OverlayItem overlayitem = new OverlayItem(
                point, 
                Title, 
                ID
            );

            itemizedoverlay.addOverlay(overlayitem);
            mapOverlays.add(itemizedoverlay);

            Log.d("MAPVIEW", "Location Data: Lat:" + coords[0] + ", Long: " + coords[1] );

            try{
                allLocations.add(coords); // ************* this is whats failing ******************
            } catch(Exception e) {
                Log.d("MAPVIEW", "Could not add coordinate array to List, Error: " + e.toString());
            }



        }

        // ... whole bunch more unrelated stuff


}

上面是大for循环json提取器。这将使程序抛出UnsupportedOperationException

老实说，我不知道还能做什么

我以为我已经弄明白了，但显然我没有：(

（注：我想像这样存储这些，这样我就可以做到：

int minLat = Integer.MAX_VALUE;
int maxLat = Integer.MIN_VALUE;
int minLon = Integer.MAX_VALUE;
int maxLon = Integer.MIN_VALUE;

for (int[] l : allLocations) { 

    int lat = (int) l[0];
    int lon = (int) l[1];


    maxLat = Math.max(lat, maxLat);
    minLat = Math.min(lat, minLat);
    maxLon = Math.max(lon, maxLon);
    minLon = Math.min(lon, minLon);

 }

---

我看不到您已初始化列表的位置。您必须先初始化列表才能使用它

allLocations = new ArrayList<int[]>();

---

未获得编译异常。该方法采用array参数。请检查：

我看不出您在哪里初始化了列表。必须先初始化列表才能使用它

allLocations = new ArrayList<int[]>();

---

没有得到编译异常。该方法采用array参数。请检查：

AH！！我们开始了！看，我试图这么做，但由于我是一个新手，我一定是在什么地方弄乱了语法，因为Eclipse..在我键入最终文本时创建了整个类重写方法）字符，但仍然出错，所以我想我走错了路：（感谢您的超快速响应！感谢上帝。我刚刚花了一个小时制作和制作了其他非必要的东西。Php让事情变得如此简单，但我必须承认，java变得非常棒。啊！！我们开始了！看，我试着这么做，但作为一个新手，我一定是在什么地方弄乱了语法，因为Eclipse..创建了整个当我输入最后一个）字符时，类重写方法仍然出错，所以我想我走错了路：（感谢您的超快速响应！感谢上帝。我只花了一个小时来铸造和做其他非必要的东西。Php让事情变得如此简单，但我必须承认，java变得非常棒。

Arrays.asList