我有一个java代码文件，
public class PropertyRequestService {
static String result;
PropertiesList localProperty = new PropertiesList();
List<PropertiesList> Properties;
public List<PropertiesList> getAllPropertiesStuff() {
JSONArray json = null;
try {
HttpClient client = new DefaultHttpClient();
HttpPost httppost = new HttpPost(
"Given URL");
List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(2);
nameValuePairs
.add(Passing parameter));
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
HttpResponse response = client.execute(httppost);
// HttpEntity entity = response.getEntity();
// if (entity != null) {
/*
* result = EntityUtils.toString(entity); Log.i("RESPONSE=",
* result);
*/
// List<PropertiesList> tst=(List<PropertiesList>)response;
ArrayList<String> jsonstring = getJSONString(response);
System.out.println("jsonString : " + jsonstring);
json = new JSONArray(jsonstring);
localProperty.angle=30;
localProperty.PropertyID =Integer.parseInt(json.getString(0));
localProperty.Latitude =Double.parseDouble(json.getString(2));
localProperty.Longitude = Double.parseDouble(json.getString(3));
localProperty.PropertyPrice = Integer.parseInt(json.getString(4));
localProperty.PropertyAddress = json.getString(1);
localProperty.listfrom=0;
Properties.add(localProperty);
} catch (Exception e1) {
e1.printStackTrace();
}
return Properties;
}
public ArrayList<String> getJSONString(HttpResponse response) {
try {
HttpEntity entity = response.getEntity();
String result = EntityUtils.toString(entity);
InputStream stream = new ByteArrayInputStream((result.replace("&",
" ")).getBytes("UTF-8"));
DocumentBuilder builder = DocumentBuilderFactory.newInstance()
.newDocumentBuilder();
Document doc = builder.parse(stream);
NodeList n1 = doc.getElementsByTagName("PropertyID");
NodeList n2 = doc.getElementsByTagName("Address");
NodeList n3 = doc.getElementsByTagName("Lat");
NodeList n4 = doc.getElementsByTagName("Lng");
NodeList n5 = doc.getElementsByTagName("Price");
Node nn1 = n1.item(0);
Node nn2 = n2.item(0);
Node nn3 = n3.item(0);
Node nn4 = n4.item(0);
Node nn5 = n5.item(0);
String str1 = nn1.getFirstChild().getNodeValue();
String str2 = nn2.getFirstChild().getNodeValue();
String str3 = nn3.getFirstChild().getNodeValue();
String str4 = nn4.getFirstChild().getNodeValue();
String str5 = nn5.getFirstChild().getNodeValue();
ArrayList<String> nodes = new ArrayList<String>();
nodes.add(str1);
nodes.add(str2);
nodes.add(str3);
nodes.add(str4);
nodes.add(str5);
System.out.println("Node value : " + nodes);
return nodes;
} catch (ParserConfigurationException e) {
e.printStackTrace();
} catch (SAXException e) {
e.printStackTrace();
} catch (IllegalStateException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}
}
和PropertiesList类，
public class PropertiesList {
public int angle;
public int PropertyID;
public int PropertyPrice;
public String PropertyAddress;
public Double Latitude;
public Double Longitude;
public static int listfrom;
}
从我称之为的活动类
PropertyRequestService properties=new PropertyRequestService();
propertyRSList= properties.getAllPropertiesStuff();
问题是，在“Properties.add（localProperty）;”行附近，我确实发现Properties变量为null并且捕获了Exception。 根据我没有语法错误或逻辑错误。我错过了什么或错误的任务吗？
这是我的logcat，
05-22 17:51:46.192: W/dalvikvm(3317): threadid=1: thread exiting with uncaught exception (group=0x40018578)
05-22 17:51:46.684: E/AndroidRuntime(3317): FATAL EXCEPTION: main
05-22 17:51:46.684: E/AndroidRuntime(3317): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.BuildersUpdate/com.BuildersUpdate.PropertySearchTypes.CameraSearch}: java.lang.NullPointerException
05-22 17:51:46.684: E/AndroidRuntime(3317): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651)
05-22 17:51:46.684: E/AndroidRuntime(3317): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
05-22 17:51:46.684: E/AndroidRuntime(3317): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
05-22 17:51:46.684: E/AndroidRuntime(3317): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
05-22 17:51:46.684: E/AndroidRuntime(3317): at android.os.Handler.dispatchMessage(Handler.java:99)
05-22 17:51:46.684: E/AndroidRuntime(3317): at android.os.Looper.loop(Looper.java:130)
05-22 17:51:46.684: E/AndroidRuntime(3317): at android.app.ActivityThread.main(ActivityThread.java:3687)
05-22 17:51:46.684: E/AndroidRuntime(3317): at java.lang.reflect.Method.invokeNative(Native Method)
05-22 17:51:46.684: E/AndroidRuntime(3317): at java.lang.reflect.Method.invoke(Method.java:507)
05-22 17:51:46.684: E/AndroidRuntime(3317): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
05-22 17:51:46.684: E/AndroidRuntime(3317): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
05-22 17:51:46.684: E/AndroidRuntime(3317): at dalvik.system.NativeStart.main(Native Method)
05-22 17:51:46.684: E/AndroidRuntime(3317): Caused by: java.lang.NullPointerException
05-22 17:51:46.684: E/AndroidRuntime(3317): at com.BuildersUpdate.PropertySearchTypes.PropertyRequestService.getAllPropertiesStuff(PropertyRequestService.java:90)
05-22 17:51:46.684: E/AndroidRuntime(3317): at com.BuildersUpdate.PropertySearchTypes.CameraSearch.onCreate(CameraSearch.java:200)
05-22 17:51:46.684: E/AndroidRuntime(3317): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
05-22 17:51:46.684: E/AndroidRuntime(3317): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615)
请建议我并纠正我！在此先感谢!!
答案 0 :(得分：4)
在访问之前，您需要实例化Properties。使用：
List<PropertiesList> Properties = new ArrayList<>();
而不是：
List<PropertiesList> Properties;
BTW，根据java命名约定，变量应以小写字母开头，因此最好使用properties代替。
答案 1 :(得分：2)
您尚未初始化List<Properties> Properties。您刚刚创建了它的引用。
List<Properties> Properties = new ArrayList<Properties>();
答案 2 :(得分：2)
您刚刚定义了一个引用属性，它将指向ArrayList类型的对象。您还需要使用 new（）运算符创建实际对象。
List<PropertiesList> Properties = new ArrayList<>();
然后您可以在其中添加数据。
Properties.add(localProperty);
照顾你的namings 。变量，函数必须是驼峰，即以小写字母开头，后续单词以大写字母开头。以caps开头的单词通常是类的名称。