我目前正在从事我的高级项目，其中涉及从数据库获取数据并将其存储，然后将其显示在应用程序上。所以我最近遇到了问题，代码主要返回两个错误:
RuntimeException:不确定是什么原因导致的NullPointerException:由于busList 数组返回空
这是我的代码:
Activity: ShowResults.java
public class ShowResults extends ActionBarActivity {
private static Connection connection = null;
private static String[] busList;
public double lat=24.197910, lon=55.678712;
public static double[][] locCoords = {{24.214649, 55.705841},
{24.340635, 55.477802}, {24.221663, 55.692266},
{24.195968, 55.682879}, {24.196066, 55.679534}, {24.197910, 55.678712}, {24.198966, 55.677567}, {24.199936, 55.677314}, {24.200635, 55.677801}};
public static String[] BldNames = {"Saih Bin Ammar Hostel", "Kowaitat Hostel", "Markhaniah Hostel",
"F3 Building", "F1 Building/The labs", "CIT Building",
"H4 Building", "Crescent Building",
"H2/H3 Buildings", "User Current Location"};
//1.jdbc driver name
private static String SQL_JDBC_DRIVER = "com.microsoft.sqlserver.jdbc.SQLServerDriver";
// 2. Database URL, V_UDAY\FRAMEWORK is ServerName and JSF is DataBase name
private static String URL
= "jdbc:sqlserver://NCMSVTRNSDB.aa.uaeu.ac.ae;databaseName=busTable";
//3.Database credentials
private static String USERNAME = "username";//UserName
private static String PASSWORD = "pass";//Password
public static String[] arr;
public static Connection getLocalConnection(double cLat,double cLon) {
// PrintWriter writer = new PrintWriter("l.txt");
Statement stmt = null;
try {
Class.forName(SQL_JDBC_DRIVER);// Register jdbc driver
//4. open a connection
connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
stmt = connection.createStatement();
String sql;
sql = "Select ID, NAME, DT_UPDATE,LON,LAT From mobile";
ResultSet rs = stmt.executeQuery(sql);
//STEP 5: Extract data from result set
String result = "";
busList = new String[128];//
int i = 0;
double dist;
double l,l2;
while (rs.next()) {
//Retrieve by column name
String id = rs.getString("ID");
String name = rs.getString("NAME");
String first = rs.getString("DT_UPDATE");
String lat = rs.getString("LAT");
String lon = rs.getString("LON");
Calendar c = Calendar.getInstance();
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-mm-dd hh:mm:ss");
String current = sdf.format(c.getTime());
if (isCurrent(first) == true) {
if (name.contains("Hyundai") || name.contains("Coaster")) {
result = "Bus:" + name + "\nTime:" + first + "\n" + calcTime(first, current);
l = Double.parseDouble(lat);
l2 = Double.parseDouble(lon);
dist = calcDist(cLat, cLon, l, l2);
result += "\nDistance: " + dist;
result += "\nClosest Building: " + closestBldg(l, l2);
result += "\n On/Off Campus: " + onOffCampus(l, l2);
busList[i] = result;
}
i++;
}
else{
result = "Bus:" + name + "\nTime:" + first + "\n" + calcTime(first, current);
l = Double.parseDouble(lat);
l2 = Double.parseDouble(lon);
dist = calcDist(24.197910, 55.678712, l, l2);
result += "\nDistance: " + dist;
result += "\nClosest Building: " + closestBldg(l, l2);
result += "\n Om/Off Campus: " + onOffCampus(l, l2);
busList[i] = result;
}
}
//STEP 6: Clean-up environment
rs.close();
stmt.close();
setConnectionClose();
System.out.println("Database Connection Closed");
} catch (Exception e) {
e.printStackTrace();
System.err.println("Exception in getLocalConeection() " + e.getMessage());
}
return connection;
}
public static void setConnectionClose() throws SQLException {
if (connection != null) {
connection.close();
}
}
public static boolean isCurrent(String busTime) {
Calendar c = Calendar.getInstance();
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-mm-dd hh:mm:ss");
String current = sdf.format(c.getTime());
Date d1 = null;
Date d2 = null;
try {
d1 = sdf.parse(current);
d2 = sdf.parse(busTime);
//in milliseconds
long diff = d1.getTime() - d2.getTime();
long diffSeconds = diff / 1000 % 60;
long diffMinutes = diff / (60 * 1000) % 60;
long diffHours = diff / (60 * 60 * 1000) % 24;
long diffDays = diff / (24 * 60 * 60 * 1000);
if (diffDays == 0 && diffHours <= 1 && (diffMinutes <= 59 && diffMinutes >= 0) && diffSeconds >= 0) {
return true;
} else {
return false;
}
} catch (Exception e) {
e.printStackTrace();
}
return true;
}
public static String[] getBusList(){
return busList;
}
public static double calcDist(double lat1, double lon1, double lat2, double lon2) {
double R = 6371000;
double theta1 = Math.toRadians(lat1);
double theta2 = Math.toRadians(lat2);
double thetaDiff = Math.toRadians(theta2 - theta1);
double lambdaDiff = Math.toRadians(lon2 - lon1);
double a = Math.pow(Math.sin(thetaDiff / 2),2)
+ Math.cos(theta1) * Math.cos(theta2)
* Math.sin(lambdaDiff / 2) * Math.pow(Math.sin(lambdaDiff / 2),2);
double c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
double d = R * c;
return d;
}
public static String calcTime(String time1, String time2) throws ParseException {
String result;
SimpleDateFormat format = new SimpleDateFormat("yyyy-mm-dd hh:mm:ss");
Date date1 = null,date2=null;
try {
date1 = format.parse(time1);
date2 = format.parse(time2);
} catch (ParseException e) {
e.printStackTrace();
}
long diff = date2.getTime() - date1.getTime();
long secs = diff / 1000 % 60;
long mins = diff / (60 * 1000) % 60;
long hrs = diff / (60 * 60 * 1000) % 24;
long days = diff / (24 * 60 * 60 * 1000);
if (hrs > 0 && mins > 0 && secs >= 0) {
result = "ETA: " + hrs + " Hours, " + mins + " Minutes" + " and " + secs + " Seconds";
} else if (mins > 0 && secs >= 0) {
result = "ETA: " + mins + " Minutes" + " and " + secs + " Seconds";
} else if (secs >= 0.01) {
result = "ETA: " + secs + " Seconds";
} else {
result = "ETA: " + "The bus should be here";
}
return result;
}
public static String onOffCampus(double busLat, double busLon) {
double uniLat1 = 24.197690, uniLon1 = 55.677708;
double uniLat2 = 24.198316, uniLon2 = 55.685948;
double distToUni1 = calcDist(uniLat1, uniLon1, busLat, busLon);
System.out.println(distToUni1);
double distToUni2 = calcDist(uniLat2, uniLon2, busLat, busLon);
System.out.println(distToUni2);
if (distToUni1 <= 0.639822725733094 || distToUni2 <= 0.588121032252993) {
return "On";
}
return "Off";
}
public static String closestBldg(double busLat, double busLon) {
double dist, lat1, lon1, min;
int mi = 0;
lat1 = locCoords[0][0];
lon1 = locCoords[0][1];
min = calcDist(lat1, lon1, busLat, busLon);
for (int k = 1; k < locCoords.length; k++) {
lat1 = locCoords[k][0];
lon1 = locCoords[k][1];
dist = calcDist(lat1, lon1, busLat, busLon);
if (dist < min) {
min = dist;
mi = k;
}
}
return BldNames[mi];
}
public void populateListView(){
//build adapter
ArrayAdapter<String> adapter;
adapter = new ArrayAdapter<>(this, R.layout.activity_show_results, busList);
//config the list view
ListView list = (ListView) findViewById(R.id.listView5);
list.setAdapter(adapter);
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Bundle b = getIntent().getExtras();
if (b != null) {
if (b.containsKey("lat1")) {
lat = b.getDouble("lat1");
}
if (b.containsKey("lon1")) {
lon = b.getDouble("lon1");
}}
else{
lat = 24.197910;
lon=55.678712;
}
getIntent().removeExtra("lat1");
getIntent().removeExtra("lon1");
getLocalConnection(lat,lon);
populateListView();
}
}
Activity ShowResults XML: activity_show_results.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context="ae.ac.uaeu.bustrackerapp.ShowResults">
<ListView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/listView5"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true" />
</RelativeLayout>
XML for TextView: dat_item.xml
<?xml version="1.0" encoding="utf-8"?>
<!-- Single List Item Design -->
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/label"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:padding="10dip"
android:textSize="16dip"
android:textStyle="bold" >
</TextView>
我确信每当我调用它时，busList 都是空的，并尝试修复它，但无法修复。 这是最有可能导致我的 NullPointerExcpetion 的原因，但不知道是什么导致了 RuntimeException 这是崩溃报告:
--------- beginning of crash
05-16 21:09:15.373 1927-1927/ae.ac.uaeu.bustrackerapp E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: ae.ac.uaeu.bustrackerapp, PID: 1927
java.lang.RuntimeException: Unable to start activity ComponentInfo{ae.ac.uaeu.bustrackerapp/ae.ac.uaeu.bustrackerapp.ShowResults}: java.lang.NullPointerException: storage == null
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: storage == null
at java.util.Arrays$ArrayList.<init>(Arrays.java:38)
at java.util.Arrays.asList(Arrays.java:155)
at android.widget.ArrayAdapter.<init>(ArrayAdapter.java:128)
at ae.ac.uaeu.bustrackerapp.ShowResults.populateListView(ShowResults.java:235)
at ae.ac.uaeu.bustrackerapp.ShowResults.onCreate(ShowResults.java:260)
at android.app.Activity.performCreate(Activity.java:5933)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
感谢任何帮助/建议/反馈
最佳答案
您应该调用 populateListView();方法，当你完成填充busList时，如果没有，这个可能是null。您应该将其放在 getLocalConnection 方法的末尾。
也改变
public void populateListView(){
ArrayAdapter<String> adapter= new ArrayAdapter<>(this, R.layout.dat_item, busList);
//config the list view
ListView list = (ListView) findViewById(R.id.listView5);
list.setAdapter(adapter);
}
和
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_show_results);
//All your stuff here
}
我测试了上面的代码并且它有效，我认为你的listView为空的原因是因为busList为空。 以下是在我的测试中起作用的 populateListView() 中的代码。
public void populateListView() {
busList = new String[2];
busList[0] = "test";
busList[1] = "test1";
// build adapter
ArrayAdapter<String> adapter = new ArrayAdapter<>(this, R.layout.dat_item, busList);
// config the list view
ListView list = (ListView) findViewById(R.id.listView5);
list.setAdapter(adapter);
}
关于java - Android - NullPointerException 和 RuntimeException，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/30279309/