java - Trying to list all folders/files from internal sdcard android but get a null -

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i trying make list of files in external storage comes null. 

if (environment.getexternalstoragedirectory().exists()) {         log.i(file, "is not empty");          file[] files = environment.getexternalstoragedirectory().listfiles();          (file file : files) {             log.i("file ", file.getabsolutepath());         }     }

how make list files external directory

i exception 

caused by: java.lang.nullpointerexception                                                                                   @ com.example.sam.read.fragments.myfragment.oncreate(myfragment.java:138)                                                                                   @ android.support.v4.app.fragment.performcreate(fragment.java:1763)                                                                                   @ android.support.v4.app.fragmentmanagerimpl.movetostate(fragmentmanager.java:913)                                                                                   @ android.support.v4.app.fragmentmanagerimpl.movetostate(fragmentmanager.java:1126)                                                                                   @ android.support.v4.app.backstackrecord.run(backstackrecord.java:739)                                                                                   @ android.support.v4.app.fragmentmanagerimpl.execpendingactions(fragmentmanager.java:1489)                                                                                   @ android.support.v4.app.fragmentactivity.onstart(fragmentactivity.java:548)                                                                                   @ android.app.instrumentation.callactivityonstart(instrumentation.java:1164)                                                                                   @ android.app.activity.performstart(activity.java:5114)                                                                                   @ android.app.activitythread.performlaunchactivity(activitythread.java:2153)                                                                                   @ android.app.activitythread.handlelaunchactivity(activitythread.java:2230)                                                                                    @ android.app.activitythread.access$600(activitythread.java:141)                                                                                    @ android.app.activitythread$h.handlemessage(activitythread.java:1234)                                                                                    @ android.os.handler.dispatchmessage(handler.java:99)                                                                                    @ android.os.looper.loop(looper.java:137)                                                                                    @ android.app.activitythread.main(activitythread.java:5041)                                                                                    @ java.lang.reflect.method.invokenative(native method)                                                                                    @ java.lang.reflect.method.invoke(method.java:511)                                                                                    @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:793)                                                                                    @ com.android.internal.os.zygoteinit.main(zygoteinit.java:560)                                                                                    @ dalvik.system.nativestart.main(native method) 

you missing permission in manifest. add

<uses-permission android:name="android.permission.read_external_storage" />

to manifest.


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