java - Unable to start activityon a null object reference -

this question has answer here:

• null pointer exception - findviewbyid() 9 answers
• what nullpointerexception, , how fix it? 12 answers

the problem is:

java.lang.runtimeexception: unable start activity componentinfo{com.example.android.miwok/com.example.android.miwok.report}: java.lang.nullpointerexception: attempt invoke virtual method 'void android.widget.listview.setadapter(android.widget.listadapter)' on null object reference

so there problem listview adapter in report.java, can't figure out how fix it. point create listview arrayadapter double data type , display screen.

activity_report.xml:

<?xml version="1.0" encoding="utf-8"?> <listview xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" tools:context="com.example.android.miwok.family_members_activity" android:layout_width="match_parent" android:layout_height="match_parent" android:layout_margintop="16dp" android:layout_marginleft="16dp" android:id="@+id/result"> </listview> 

listpazymiai.xml

<?xml version="1.0" encoding="utf-8"?> <linearlayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:orientation="horizontal" android:layout_height="wrap_content" android:layout_width="match_parent" android:layout_margintop="8dp">     <textview         android:layout_width="0dp"         android:layout_height="wrap_content"         android:id="@+id/ltrez"         android:gravity="center"         android:layout_weight="1"         tools:text="first mark"         />     <textview         android:layout_width="0dp"         android:layout_height="wrap_content"         android:id="@+id/anglrez"         android:layout_weight="1"         android:gravity="center"         tools:text="second mark"         />     <textview         android:layout_width="0dp"         android:layout_height="wrap_content"         android:id="@+id/itrez"         android:layout_weight="1"         android:gravity="center"         tools:text="third mark"         /> </linearlayout> 

report.java code

package com.example.android.miwok;  import android.app.actionbar; import android.graphics.drawable.colordrawable; import android.support.v7.app.appcompatactivity; import android.os.bundle; import android.util.log; import android.widget.arrayadapter; import android.widget.gridview; import android.widget.linearlayout; import android.widget.listview; import android.widget.textview; import com.example.android.miwok.reports; import java.lang.reflect.array; import java.util.arraylist; import com.example.android.miwok.reportocard; import static android.graphics.color.black; public class report extends appcompatactivity {  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_numbers_activity);      arraylist<reportocard> pzm = new arraylist<reportocard>();     pzm.add(new reportocard(98.5, 89.6, 88.8));     pzm.add(new reportocard(88.7, 69.3, 58.2));     pzm.add(new reportocard(88.9, 59.4, 48.3));     pzm.add(new reportocard(92.8, 81.2, 87.4));     pzm.add(new reportocard(98.2, 89.1, 88.1));     pzm.add(new reportocard(23.5, 19.4, 88.7));     pzm.add(new reportocard(92.3, 59.3, 81.1));     pzm.add(new reportocard(56.5, 15.6, 18.8));     pzm.add(new reportocard(48.4, 95.6, 99.8));     pzm.add(new reportocard(45.7, 100, 10.8));      reports reportss = new reports(this, pzm);     listview listelis =(listview)findviewbyid(r.id.result);     listelis.setadapter(reportss);  } } 

reportocard.java:

package com.example.android.miwok;  import android.text.layout;  /** *created justas on 9/10/2017. */  public class reportocard {  double manglu; double mlietuviu; double mit;  public reportocard  (double anglu, double lietuviu, double it) {     manglu = anglu;     mlietuviu = lietuviu;     mit = it;  } public double getit () {     return mit; } public double getanglu () { return manglu; } public double getlietuviu () {     return mlietuviu; } } 

reports.java:

package com.example.android.miwok; import android.app.activity; import android.view.layoutinflater; import android.view.view; import android.view.viewgroup; import android.widget.arrayadapter; import android.widget.imageview; import android.widget.textview;  import com.example.android.miwok.adaptoreditor; import com.example.android.miwok.r; import com.example.android.miwok.reportocard;   import java.util.arraylist;  public class reports extends arrayadapter<reportocard> {  private static final string log_tag = reports.class.getsimplename();  public reports(activity context, arraylist<reportocard> pzm) {      super(context, 0, pzm); } @override public view getview(int position, view convertview, viewgroup parent) {     // check if existing view being reused, otherwise inflate view     view linear = convertview;     if(linear == null) {         linear = layoutinflater.from(getcontext()).inflate(r.layout.listpazymiai, parent, false);     }      reportocard pzm = getitem(position);      textview anglu = (textview) linear.findviewbyid(r.id.ltrez);      anglu.settext(""+pzm.getanglu());      textview lietuviu = (textview) linear.findviewbyid(r.id.anglrez);     lietuviu.settext(""+pzm.getlietuviu());      textview = (textview)linear.findviewbyid(r.id.itrez);     it.settext(""+pzm.getit());     return linear; }  } 

your problem listview null. need focus on 2 lines of code in report.java code:

setcontentview(r.layout.activity_numbers_activity); 

and

listview listelis =(listview)findviewbyid(r.id.result); 

when you're calling findviewbyid, implicitly using inflated activity_numbers_activity view first line of code try , find listview. problem not have listview inside activity_numbers_activity.xml!

you need move listview inside r.layout.activity_numbers_activity or call findviewbyid view listview inside of it.