Null Pointer Exception at 'if' statement [duplicate]

Question

Im getting furious, because Im still getting an error at my code:

myVar = getFiles();
(...)
public ArrayList<HashMap<String, String>> getFiles(){
    File dir = new File(new String("/sdcard/"));

    if (dir.listFiles(new myFilter()).length > 0) {
        for (File file : dir.listFiles(new myFilter())) {
            (...)
        }
    }
    return myList;
}

at if statement:

if (dir.listFiles(new myFilter()).length > 0) {

This is what i get:

01-13 22:28:42.313: W/dalvikvm(13776): threadid=1: thread exiting with uncaught exception (group=0x40c5a1f8)
01-13 22:28:42.318: E/AndroidRuntime(13776): FATAL EXCEPTION: main
01-13 22:28:42.318: E/AndroidRuntime(13776): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.remotedevice/com.example.remotedevice.Player}: java.lang.NullPointerException
01-13 22:28:42.318: E/AndroidRuntime(13776):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1967)
01-13 22:28:42.318: E/AndroidRuntime(13776):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1992)
01-13 22:28:42.318: E/AndroidRuntime(13776):    at android.app.ActivityThread.access$600(ActivityThread.java:127)
01-13 22:28:42.318: E/AndroidRuntime(13776):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1158)
01-13 22:28:42.318: E/AndroidRuntime(13776):    at android.os.Handler.dispatchMessage(Handler.java:99)
01-13 22:28:42.318: E/AndroidRuntime(13776):    at android.os.Looper.loop(Looper.java:137)
01-13 22:28:42.318: E/AndroidRuntime(13776):    at android.app.ActivityThread.main(ActivityThread.java:4511)
01-13 22:28:42.318: E/AndroidRuntime(13776):    at java.lang.reflect.Method.invokeNative(Native Method)
01-13 22:28:42.318: E/AndroidRuntime(13776):    at java.lang.reflect.Method.invoke(Method.java:511)
01-13 22:28:42.318: E/AndroidRuntime(13776):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:980)
01-13 22:28:42.318: E/AndroidRuntime(13776):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:747)
01-13 22:28:42.318: E/AndroidRuntime(13776):    at dalvik.system.NativeStart.main(Native Method)
01-13 22:28:42.318: E/AndroidRuntime(13776): Caused by: java.lang.NullPointerException
01-13 22:28:42.318: E/AndroidRuntime(13776):    at com.example.remotedevice.Player.getPlayList(Player.java:120)
01-13 22:28:42.318: E/AndroidRuntime(13776):    at com.example.remotedevice.Player.onCreate(Player.java:56)
01-13 22:28:42.318: E/AndroidRuntime(13776):    at android.app.Activity.performCreate(Activity.java:4470)
01-13 22:28:42.318: E/AndroidRuntime(13776):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1052)
01-13 22:28:42.318: E/AndroidRuntime(13776):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1931)
01-13 22:28:42.318: E/AndroidRuntime(13776):    ... 11 more

I've read this topic : Null Pointer Exception after checking with 'if' statement but havent find answear, which I could use to my code :/ I've tried few 'solutions' but still getting this error :( PLEASE HELP!

Caused by: java.lang.NullPointerException 01-13 22:28:42.318: E/AndroidRuntime(13776): at com.example.remotedevice.Player.getPlayList(Player.java:120) Which line, exactly, is 120? — Simon
– Simon, Commented Jan 13, 2014 at 21:39
as i said: "at if statement: if (dir.listFiles(new myFilter()).length > 0) {" (this is line 120) — droid
– droid, Commented Jan 14, 2014 at 8:45

laalto · Accepted Answer · 2014-01-13 21:46:08Z

0

File listFiles() may return null for example if the file is not a directory. You'll need to check for != null before accessing the length field to prevent the NPE.

Now, why isn't /sdcard a directory? On many devices it is a symbolic link. You'll have to resolve the symbolic link with getCanonicalFile() first.

Example:

File[] files = dir.getCanonicalFile().listFiles(new myFilter());
if (files != null) {   
    for (File file : files) {
        //...

Also, it's beneficial to store the result of an "expensive" method call such as listFiles() instead of calling it repeatedly.

edited Jan 13, 2014 at 21:46

answered Jan 13, 2014 at 21:38

laalto

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2 Comments

Josh Engelsma Over a year ago

I think the OP wants to know why it is returning null

droid Over a year ago

The problem was that I gave directory "/dir" instead of "/sdcard/dir"... But I saw that after your post about "symbolic link" - thanks for help!

cfred · Accepted Answer · 2014-01-13 21:45:10Z

0

According to the documentation for the listFiles(), it "Returns null if this abstract pathname does not denote a directory, or if an I/O error occurs."

Therefore, you will need to check if it is null and handle the error in these situations.

answered Jan 13, 2014 at 21:45

cfred

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