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RecyclerView throws null pointer for setAdapter even though the adapter is defined

I have a null pointer exception but I can't see where I am going wrong. I have been trying to fix this error for 2 days.
Here is the activity_main.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/recycler_view"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</RelativeLayout>
and the Code for the class MainActivity
package com.example.servicestest1;
import android.os.Bundle;
import android.util.Log;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity{
private static final String TAG = "MainActivity";
private ArrayList<String> mDescriptions = new ArrayList<>();
private ArrayList<String> mStartDates = new ArrayList<>();
private ArrayList<String> mEndDates = new ArrayList<>();
private ArrayList<String> mImageUrls = new ArrayList<>();
private ArrayList<String> mTopicList = new ArrayList<>();
RecyclerView recyclerView;
#Override
protected void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = findViewById(R.id.recycler_view);
initRecyclerViewItems();
}
private void initRecyclerViewItems() {
Log.d(TAG, "initRecyclerViewItems: preparing items");
addRecyclerViewItem("https://i.redd.it/3p6500yf3he41.jpg","Hogwarts Express","Working for the soviet union"
,"20/01/1968","20/10/1984");
addRecyclerViewItem("https://i.redd.it/s8bmctrhdxd41.jpg","Some scene about Nature","Some title",
"20/09/1897","20/03/1989");
addRecyclerViewItem("https://i.redd.it/lrbmhm707rd41.jpg","Boating","Boating in a pristine location",
"30/09/1998","31/09/1998");
initRecyclerView();
}
private void addRecyclerViewItem(String imageUrl, String topic, String description, String startDate, String endDate){
Log.w(TAG, "addRecyclerViewItem: called", null);
mImageUrls.add(imageUrl);
mTopicList.add(topic);
mStartDates.add(startDate);
mEndDates.add(endDate);
mDescriptions.add(description);
}
private void initRecyclerView(){
RecyclerViewAdapter adapter = new RecyclerViewAdapter(this,mTopicList,mDescriptions,
mStartDates,mEndDates,mImageUrls);
recyclerView.setAdapter(adapter);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
}
}
The recyclerView.setAdapter returns a NullPointer exeception even though I have defined the adapter.
and the code for the RecyclerView adapter
package com.example.servicestest1;
import android.content.Context;
import android.net.Uri;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.TextView;
import android.widget.Toast;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import java.util.ArrayList;
public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.ViewHolder>{
private static final String TAG = "RecyclerViewAdapter";
private ArrayList<String> mTopicListOfTheEvent;
private ArrayList<String> mDescriptionListOfTheEvent;
private ArrayList<String> mStartDateListOfTheEvent;
private ArrayList<String> mEndDateListOfTheEvent;
private ArrayList<String> mImageListDescribingTheEvent;
private Context mContext;
RecyclerViewAdapter(Context context,
ArrayList<String> topicListOfTheEvent,
ArrayList<String> descriptionListOfTheEvent,
ArrayList<String> startDateListOfTheEvent,
ArrayList<String> endDateListOfTheEvent,
ArrayList<String> imageListDescribingTheEvent){
this.mContext = context;
this.mTopicListOfTheEvent = topicListOfTheEvent;
this.mDescriptionListOfTheEvent = descriptionListOfTheEvent;
this.mStartDateListOfTheEvent = startDateListOfTheEvent;
this.mEndDateListOfTheEvent = endDateListOfTheEvent;
this.mImageListDescribingTheEvent = imageListDescribingTheEvent;
}
#NonNull
#Override
public RecyclerViewAdapter.ViewHolder onCreateViewHolder(#NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.activity_recycler_view_layout,parent,true);
return new ViewHolder(view);
}
#Override
public void onBindViewHolder(#NonNull RecyclerViewAdapter.ViewHolder holder, int position) {
Log.d(TAG, "onBindViewHolder: called");
holder.descriptionOfTheEvent.setText(mDescriptionListOfTheEvent.get(position));
holder.imageDescribingTheEvent.setImageURI(Uri.parse(mImageListDescribingTheEvent.get(position)));
holder.startDateOfTheEvent.setText(mStartDateListOfTheEvent.get(position));
holder.endDateOfTheEvent.setText(mEndDateListOfTheEvent.get(position));
holder.topicListOfTheEvent.setText(mTopicListOfTheEvent.get(position));
holder.parentLayout.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Log.d(TAG, "onClick: Clicked on");
Toast.makeText(mContext,"You pressed me",Toast.LENGTH_SHORT).show();
}
});
}
#Override
public int getItemCount() {
return mTopicListOfTheEvent.size();
}
class ViewHolder extends RecyclerView.ViewHolder{
TextView descriptionOfTheEvent;
TextView topicListOfTheEvent;
TextView startDateOfTheEvent;
TextView endDateOfTheEvent;
ImageView imageDescribingTheEvent;
LinearLayout parentLayout;
ViewHolder(#NonNull View itemView) {
super(itemView);
parentLayout = itemView.findViewById(R.id.recycler_view_item);
}
}
}
and the code for the activity_recycler_view_layout.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:id="#+id/recycler_view_item">
<!-- The code for the AppBar -->
<androidx.appcompat.widget.Toolbar
android:layout_width="match_parent"
android:layout_height="44dp"
android:background="#FFFEFE"
android:elevation="5dp"
tools:targetApi="lollipop">
<RelativeLayout
android:id="#+id/relativeLayout"
android:layout_width="match_parent"
android:layout_height="match_parent">
<ImageView
android:id="#+id/imageView"
android:layout_width="wrap_content"
android:layout_height="44dp"
android:layout_alignParentStart="true"
android:layout_alignParentLeft="true"
android:layout_marginTop="8dp"
android:src="#drawable/bottom_lotus"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:ignore="ContentDescription" />
<ImageView
android:id="#+id/imageView2"
android:layout_width="11dp"
android:layout_height="44dp"
android:layout_marginStart="18dp"
android:layout_marginLeft="18dp"
android:layout_marginTop="17dp"
android:layout_marginBottom="10dp"
android:src="#drawable/arrow"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:ignore="ContentDescription" />
<TextView
android:id="#+id/textView"
android:layout_width="66dp"
android:layout_height="44dp"
android:layout_marginStart="49dp"
android:layout_marginLeft="49dp"
android:layout_marginTop="13dp"
android:layout_marginBottom="10dp"
android:lineHeight="21sp"
android:text="Services"
android:textColor="#403E42"
android:textSize="16sp"
app:fontFamily="#font/roboto_condensed_regular"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<de.hdodenhof.circleimageview.CircleImageView
android:id="#+id/profile_picture"
android:layout_width="wrap_content"
android:layout_height="44dp"
android:layout_alignParentRight="true"
android:layout_marginLeft="4dp"
android:layout_marginTop="4dp"
android:layout_marginBottom="4dp"
android:src="#drawable/ic_launcher_background"
android:layout_alignParentEnd="true" />
</RelativeLayout>
</androidx.appcompat.widget.Toolbar>
<RelativeLayout
android:layout_width="348dp"
android:layout_height="296dp"
android:layout_margin="6dp">
<ImageView
android:layout_width="348dp"
android:layout_height="296dp"
android:src="#drawable/images" />
<TextView
android:id="#+id/topic_text_view"
android:layout_width="wrap_content"
android:layout_height="28dp"
android:layout_marginStart="25dp"
android:layout_marginLeft="25dp"
android:layout_marginTop="25dp"
android:alpha="0.41"
android:text="It's His Birthday"
android:textColor="#f93f3f"
android:textSize="21sp"
app:fontFamily="#font/roboto_condensed_bold" />
<!--This LinearLayout is used for drawing the text inside the rectangle -->
<LinearLayout
android:layout_width="242dp"
android:layout_height="51dp"
android:layout_marginLeft="26dp"
android:layout_marginTop="64dp"
android:background="#drawable/rectangle"
android:orientation="vertical"
android:layout_marginStart="26dp">
<TextView
android:layout_width="198dp"
android:layout_height="32dp"
android:gravity="center"
android:lineHeight="16dp"
android:text="This is Sample Text"
android:textColor="#ffffff"
android:textSize="12sp"
app:fontFamily="#font/roboto_bold" />
</LinearLayout>
<TextView
android:layout_width="37dp"
android:layout_height="19dp"
android:layout_marginStart="26dp"
android:layout_marginLeft="26dp"
android:layout_marginTop="142dp"
android:lineHeight="19dp"
android:text="Dates"
android:textColor="#FFFFFF"
android:textSize="14sp"
app:fontFamily="#font/roboto_condensed_bold" />
<LinearLayout
android:layout_width="86dp"
android:layout_height="35dp"
android:layout_marginStart="62dp"
android:layout_marginLeft="62dp"
android:layout_marginTop="142dp"
android:orientation="vertical">
<TextView
android:id="#+id/start_date_of_the_event"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:lineHeight="16dp"
android:text="12 June 2019"
android:textColor="#ffffff"
android:textSize="12sp"
app:fontFamily="#font/roboto" />
<TextView
android:id="#+id/end_date_of_the_event"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:lineHeight="16dp"
android:text="13 June 2019"
android:textColor="#ffffff"
android:textSize="12sp"
app:fontFamily="#font/roboto" />
</LinearLayout>
</RelativeLayout>
<TextView
android:id="#+id/reject_button"
android:layout_width="35dp"
android:layout_height="16dp"
android:layout_marginStart="160dp"
android:layout_marginLeft="160dp"
android:layout_marginTop="15dp"
android:clickable="true"
android:text="REJECT"
android:textColor="#4B0082"
android:textStyle="bold"
tools:ignore="KeyboardInaccessibleWidget" />
<Button
android:id="#+id/accept_button"
android:layout_width="103dp"
android:layout_height="37dp"
android:layout_marginStart="248dp"
android:layout_marginLeft="248dp"
android:background="#4B0082"
android:text="ACCEPT"
android:textColor="#ffffff"
android:textSize="20sp" />
</LinearLayout>
And the here are the errors
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.servicestest1/com.example.servicestest1.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setAdapter(androidx.recyclerview.widget.RecyclerView$Adapter)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setAdapter(androidx.recyclerview.widget.RecyclerView$Adapter)' on a null object reference
at com.example.servicestest1.MainActivity.initRecyclerView(MainActivity.java:53)
at com.example.servicestest1.MainActivity.initRecyclerViewItems(MainActivity.java:38)
at com.example.servicestest1.MainActivity.onCreate(MainActivity.java:27)
at android.app.Activity.performCreate(Activity.java:7136)
at android.app.Activity.performCreate(Activity.java:7127)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048) 
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808) 
at android.os.Handler.dispatchMessage(Handler.java:106) 
at android.os.Looper.loop(Looper.java:193) 
at android.app.ActivityThread.main(ActivityThread.java:6669) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) 

recyclerView variable is set after its usage, so it's null when you try to set adapter.
Assign recyclerView before setting the adapter
protected void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = findViewById(R.id.recycler_view);
initRecyclerViewItems();
}

in Java, calling findViewById(...) initializes the view variable. The variable is usually null when findViewById(..) hasn't been called yet or has been called with an id from a layout which hasn't been inflated yet. In your case. You can fix the error simply by changing your onCreate method.
#Override
protected void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = findViewById(R.id.recycler_view); //recyclerView gets initialized here
initRecyclerViewItems();
}
Google docs on findViewById

It takes some time to inflate recycler view. Try to add waiting cycle:
recyclerView = findViewById(R.id.recycler_view);
while (recyclerView == null){
Thread.sleep(1);
}
init();

android java Null point exeption at view.setonclicklistener at the secend init why they do not match

I have this problem and it shows me following error
please help me:
I get a NullPointerException in init2(). Apperently sms is null.
I don't understand the problem
Process: com.example.android.projectdestage, PID: 11049
java.lang.RuntimeException: Unable to start activity
ComponentInfo{com.example.android.projectdestage/com.example.android.projectdestage.MainActivity}:
java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.view.View.setOnClickListener(android.view.View$OnClickListener)'
on a null object reference
at
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2984)
at
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3045)
at android.app.ActivityThread.-wrap14(ActivityThread.java)
at
android.app.ActivityThread$H.handleMessage(ActivityThread.java:1642)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6776)
at java.lang.reflect.Method.invoke(Native Method)
at
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1518)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1408)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.view.View.setOnClickListener(android.view.View$OnClickListener)'
on a null object reference
at
com.example.android.projectdestage.MainActivity.init2(MainActivity.java:60)
at
com.example.android.projectdestage.MainActivity.onCreate(MainActivity.java:38)
at android.app.Activity.performCreate(Activity.java:6956)
at
android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1126)
at
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2927)
at
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3045) 
at android.app.ActivityThread.-wrap14(ActivityThread.java) 
at
android.app.ActivityThread$H.handleMessage(ActivityThread.java:1642) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:154) 
at android.app.ActivityThread.main(ActivityThread.java:6776) 
at java.lang.reflect.Method.invoke(Native Method) 
at
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1518) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1408)
****this is my main activity****
import android.app.Dialog;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GoogleApiAvailability;
public class MainActivity extends AppCompatActivity
{
private Button sms;
private Button btnMap;
private static final String TAG = "MainActivity";
private static final int ERROR_DIALOG_REQUEST = 9001;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.setContentView(R.layout.activity_main);
if(isServicesOK()){
init();
init2();
}
}
private void init(){
Button btnMap = (Button) findViewById(R.id.btnMap);
btnMap.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Intent intent = new Intent(MainActivity.this, MapActivity.class);
startActivity(intent);
}
});
}
private void init2()
{
Button sms = (Button) findViewById(R.id.sms);
sms.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent message = new Intent(MainActivity.this, MainActivity2.class);
startActivity(message);
}
});
}
public boolean isServicesOK()
{
Log.d(TAG, "isServicesOK: checking google services version");
int available = GoogleApiAvailability.getInstance().isGooglePlayServicesAvailable(MainActivity.this);
if(available == ConnectionResult.SUCCESS)
{
// koulchi mli7 map request
Log.d(TAG, "isServicesOK: Google Play Services is working");
return true;
}
else if(GoogleApiAvailability.getInstance().isUserResolvableError(available))
{
//test d erreur
Log.d(TAG, "isServicesOK: an error occured but we can fix it");
Dialog dialog = GoogleApiAvailability.getInstance().getErrorDialog(MainActivity.this, available, ERROR_DIALOG_REQUEST);
dialog.show();
}else
{
Toast.makeText(this, "You can't make map requests", Toast.LENGTH_SHORT).show();
}
return false;
}
}
`**this is my mainactivity xml**`
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 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"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.android.projectdestage.MainActivity">
<Button
android:id="#+id/btnMap"
android:layout_width="87dp"
android:layout_height="45dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="244dp"
android:text="#string/map"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.43"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="#+id/smsbtn"
android:layout_width="wrap_content"
android:layout_height="43dp"
android:layout_marginBottom="136dp"
android:layout_marginEnd="8dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:text="#string/enter_your_message"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.43"
app:layout_constraintStart_toStartOf="parent" />
</android.support.constraint.ConstraintLayout>
**and the main2activity xml**
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:orientation="vertical"
tools:context="com.example.android.projectdestage.MainActivity2">
<TextView
android:id="#+id/editText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/enter_your_message"
android:textSize="30sp" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="519dp"
android:orientation="vertical">
<TextView
android:id="#+id/editText2"
android:layout_width="385dp"
android:layout_height="410dp"
android:layout_marginTop="50dp"
android:layout_weight="1"
android:text="#string/textview" />
<Button
android:id="#+id/btnSendSMSendSms"
android:layout_width="wrap_content"
android:layout_height="250dp"
android:layout_marginLeft="150dp"
android:layout_marginStart="150dp"
android:layout_marginVertical="110dp"
android:layout_weight="1"
android:text="#string/sendsms"
tools:targetApi="o" />
</LinearLayout>
</LinearLayout>
and the the mapactivity xml
i think the main problem is here
<?xml version="1.0" encoding="utf-8"?>
<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">
<fragment 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:id="#+id/map"
tools:context=".MapsActivity"
android:name="com.google.android.gms.maps.SupportMapFragment" />
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="50dp"
android:layout_marginTop="10dp"
android:layout_marginRight="10dp"
android:layout_marginLeft="10dp"
android:elevation="10dp"
android:background="#drawable/white_border"
android:id="#+id/relLayout1" tools:targetApi="lollipop">
<ImageView
android:layout_width="15dp"
android:layout_height="15dp"
android:id="#+id/ic_magnify"
android:layout_centerVertical="true"
android:layout_marginLeft="10dp"
android:src="#drawable/ic_magnify" android:contentDescription="#string/todoo" android:layout_marginStart="10dp" />
<AutoCompleteTextView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_toRightOf="#+id/ic_magnify"
android:layout_centerVertical="true"
android:textSize="15sp"
android:textColor="#000"
android:id="#+id/input_search"
android:background="#null"
android:hint="#string/enter_address_city_or_zip_code"
android:imeOptions="actionSearch" android:layout_toEndOf="#+id/ic_magnify" />
</RelativeLayout>
<ImageView
android:layout_width="40dp"
android:layout_height="40dp"
android:layout_below="#id/relLayout1"
android:layout_alignParentRight="true"
android:layout_marginRight="10dp"
android:layout_marginTop="10dp"
android:scaleType="centerCrop"
android:id="#+id/ic_gps"
android:src="#drawable/ic_gps" android:contentDescription="#string/todo" android:layout_alignParentEnd="true" android:layout_marginEnd="10dp" />
<ImageView
android:layout_width="40dp"
android:layout_height="40dp"
android:id="#+id/place_picker"
android:layout_marginLeft="10dp"
android:layout_marginTop="15dp"
android:scaleType="centerCrop"
android:layout_below="#+id/relLayout1"
android:src="#drawable/ic_map" android:contentDescription="#string/todoml" android:layout_marginStart="10dp" />
<ImageView
android:layout_width="40dp"
android:layout_height="40dp"
android:layout_below="#+id/place_picker"
android:layout_marginLeft="10dp"
android:layout_marginTop="15dp"
android:scaleType="centerCrop"
android:id="#+id/place_info"
android:src="#drawable/ic_info" android:layout_marginStart="10dp" android:contentDescription="#string/todoop" />
</RelativeLayout>
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thank you
thank you

Button sms = (Button) findViewById(R.id.sms); returns null
This means he can not find R.id.sms in your activity_main.xml layout.
Maybe a typo or copy paste error? Check if this button's ID in this file really is sms.
Also if you have multiple layouts for different screen sizes, etc. Check all of them.

You have smsBtn as an id for sms Button in your activity_main.xml, whereas you've passed sms as id. So id with sms is not found and so button is null and throws null pointer exception.
There is better approach that can accomplish this using Butterknife library:
public class MainActivity extends AppCompatActivity
{
#BindView(R.id.smsBtn)
private Button sms;
#BindView(R.id.btnMap)
private Button btnMap;
private static final String TAG = "MainActivity";
private static final int ERROR_DIALOG_REQUEST = 9001;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.setContentView(R.layout.activity_main);
ButterKnife.bind(this);
}
#OnClick({R.id.btnMap, R.id.smsBtn})
public void onClick(View view) {
switch (view.getId()) {
case R.id.btnMap:
//Your functionality
break;
case R.id.smsBtn:
//Your functionality
break;
}
}
}
//Dependency for ButterKnife library
implementation 'com.jakewharton:butterknife:8.8.1'
annotationProcessor 'com.jakewharton:butterknife-compiler:8.8.1'
//Butterknife link
https://github.com/JakeWharton/butterknife

animation java.lang.NullPointerException error [duplicate]

This question already has answers here:
Why does my Android app crash with a NullPointerException when initializing a variable with findViewById(R.id.******) at the beginning of the class?
(9 answers)
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 4 years ago.
When i want to run app in my device i get this error in logcat
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.allo/com.example.android.allo.WelcomeActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.LinearLayout.setAnimation(android.view.animation.Animation)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6541)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.LinearLayout.setAnimation(android.view.animation.Animation)' on a null object reference
at com.example.android.allo.WelcomeActivity.onCreate(WelcomeActivity.java:24)
at android.app.Activity.performCreate(Activity.java:6975)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1213)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892) 
at android.app.ActivityThread.-wrap11(Unknown Source:0) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593) 
at android.os.Handler.dispatchMessage(Handler.java:105) 
at android.os.Looper.loop(Looper.java:164) 
at android.app.ActivityThread.main(ActivityThread.java:6541) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767) 
WelcomActivty.java :
import android.app.Activity;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.view.animation.Animation;
import android.view.animation.AnimationUtils;
import android.widget.Button;
import android.widget.LinearLayout;
public class WelcomeActivity extends AppCompatActivity {
LinearLayout l1,l2;
Button btnsub;
Animation uptodown,downtoup;
LinearLayout linearLayout=(LinearLayout) findViewById(R.id.l1);
LinearLayout linearLayout1=(LinearLayout) findViewById(R.id.l2);
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.welcome);
java.text.DateFormat dateFormat = android.text.format.DateFormat.getDateFormat(getApplicationContext());
btnsub = (Button)findViewById(R.id.buttoncom);
uptodown = AnimationUtils.loadAnimation(this,R.anim.uptodown);
downtoup = AnimationUtils.loadAnimation(this,R.anim.downtoup);
l1.setAnimation(uptodown);
l2.setAnimation(downtoup);
}
protected void onStart(){
super.onStart();
linearLayout.startAnimation(uptodown);
linearLayout1.startAnimation(downtoup);
}
public void com(View view){
Intent intent = new Intent(this, Login.class);
Button buttoncom = (Button) findViewById(R.id.buttoncom);
startActivity(intent);
}
}
welcome.xml:
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.example.android.allo.WelcomeActivity"
android:background="#drawable/background"
android:orientation="vertical">
<LinearLayout
android:id="#+id/l1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical"
>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:layout_marginTop="120dp"
android:text="#string/bienvenue"
android:textColor="#color/lightorange"
android:textSize="60sp"
android:textStyle="bold" />
<TextView
android:textColor="#color/lightorangedark"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:text="#string/dans_quoi"
android:textAlignment="center"
android:textSize="20sp"
/>
</LinearLayout>
<LinearLayout
android:id="#+id/l2"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginTop="115dp"
android:background="#drawable/spaceullustration"
android:orientation="vertical">
<Button
android:id="#+id/buttoncom"
android:layout_width="145dp"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:background="#drawable/buttonstyle"
android:text="#string/button_commencer" />
</LinearLayout>
activity_login.xml
<RelativeLayout 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"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#drawable/backgroudlogin"
tools:context=".Login">
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:layout_marginBottom="232dp"
android:background="#drawable/ic_email_button"
android:hint=" Email"/>
<EditText
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:layout_marginBottom="159dp"
android:background="#drawable/ic_email_button"
android:hint=" password"/>
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:layout_marginBottom="70dp"
android:background="#drawable/ic_sign_in"
android:text="Sign IN" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:layout_marginBottom="20dp"
android:text="create an account"
android:textSize="20dp"
android:textColor="#FFFFFF"/>
Login.xml
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
public class Login extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
}
}
i know, there is a lot of question in the forum with the same subject but I can not find the solution, so please do not mark the question as duplicated

You should do this way -
public class WelcomeActivity extends AppCompatActivity {
Button btnsub;
Animation uptodown,downtoup;
LinearLayout linearLayout;
LinearLayout linearLayout1;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.welcome);
java.text.DateFormat dateFormat = android.text.format.DateFormat.getDateFormat(getApplicationContext());
linearLayout=(LinearLayout) findViewById(R.id.l1);
linearLayout1=(LinearLayout) findViewById(R.id.l2);
btnsub = (Button)findViewById(R.id.buttoncom);
uptodown = AnimationUtils.loadAnimation(this,R.anim.uptodown);
downtoup = AnimationUtils.loadAnimation(this,R.anim.downtoup);
linearLayout.setAnimation(uptodown);
linearLayout1.setAnimation(downtoup);
}
}

app keeps stopping when clicks on imagebutton [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 5 years ago.
$ error in androidmonitor
02-02 14:22:48.870 3269-3269/com.example.applincatio.t E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.applincatio.t, PID: 3269
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.applincatio.t/com.example.applincatio.t.moddle}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.webkit.WebView.setWebChromeClient(android.webkit.WebChromeClient)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.webkit.WebView.setWebChromeClient(android.webkit.WebChromeClient)' on a null object reference
at com.example.applincatio.t.moddle.onCreate(moddle.java:20)
at android.app.Activity.performCreate(Activity.java:6664)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707) 
at android.app.ActivityThread.-wrap12(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:154) 
at android.app.ActivityThread.main(ActivityThread.java:6077) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755) 
$main activity.java
package com.example.applincatio.t;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageButton;
import android.widget.ImageView;
import static com.example.applincatio.t.R.*;
import static com.example.applincatio.t.R.id.moddle1;
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
ImageView moddle;
ImageButton outlook;
ImageButton contactus;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(layout.activity_main);
moddle = (ImageView) findViewById(moddle1);
ImageView moddle = (ImageView) findViewById(moddle1);
moddle.setOnClickListener(this);
}
public void onClick(View view) {
switch (view.getId()) {
case moddle1:
Intent imprintIntent = new Intent(MainActivity.this, moddle.class);
imprintIntent.putExtra("webivew", moddle1);
this.startActivity(imprintIntent);
break;
case id.outlook:
Intent contactIntent = new Intent(MainActivity.this, moddle.class);
// contactIntent.putExtra("webivewContact", outlook);
this.startActivity(contactIntent);
break;
case id.contactus:
Intent aboutIntent = new Intent(MainActivity.this, moddle.class);
//aboutIntent.putExtra("webivewAbout", contactus);
this.startActivity(aboutIntent);
break;
}
}
}
$moddle.java
package com.example.applincatio.t;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.webkit.WebChromeClient;
import android.webkit.WebView;
public class moddle extends AppCompatActivity {
String url;
WebView webView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
webView = (WebView) findViewById(R.id.web_link);
webView.clearCache(true);
webView.clearHistory();
webView.getSettings().setJavaScriptEnabled(true);
Intent intent = this.getIntent();
if (intent != null) {
Bundle data = getIntent().getExtras();
if (data.containsKey("webivew")) { //i have changed this param to match the intent passed
url = data.getString("webivew");
}
if (data.containsKey("webivewContact")) {
url = data.getString("webivewContact");
}
if (data.containsKey("webivewAbout")) {
url = data.getString("webivewAbout");
}
webView.setWebChromeClient(new WebChromeClient() {
public void onProgressChanged(WebView wView, int progress) {
// webViewActivity.setTitle("Loading...");
// webViewActivity.requestWindowFeature(progress * 100);
if(progress == 100) {
// webViewActivity.setTitle(R.string.app_name);
}
}
});
webView.loadUrl(url);
}
}
}
$activitymain.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:id="#+id/activity_main"
android:layout_width="match_parent"
android:background="#drawable/p"
android:layout_height="match_parent"
android:orientation="vertical"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context="com.example.applincatio.t.MainActivity"
android:weightSum="1">
<GridLayout
android:layout_width="match_parent"
android:rowCount="4"
android:columnCount="2"
android:layout_height="530dp"
android:alignmentMode="alignMargins"
android:columnOrderPreserved="false"
android:id="#+id/gridview"
android:padding="14dp">
<LinearLayout
android:layout_gravity="center_horizontal|center_vertical"
android:layout_margin="16dp"
android:orientation="vertical"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:id="#+id/moddle1"
android:src="#drawable/moddle"/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="MODDLE"
android:textColor="#fff"
android:textStyle="bold"
android:textAppearance="#style/TextAppearance.AppCompat.Headline" />
</LinearLayout>
<LinearLayout
android:layout_gravity="center_horizontal|center_vertical"
android:layout_margin="16dp"
android:orientation="vertical"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
<ImageButton
android:layout_width="96dp"
android:layout_height="139dp"
android:id="#+id/outlook"
android:layout_gravity="center"
android:src="#drawable/ou"/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="OUTLOOK"
android:gravity="bottom"
android:textAlignment="center"
android:textColor="#ffffff"
android:textStyle="bold"
android:textAppearance="#style/TextAppearance.AppCompat.Headline" />
</LinearLayout>
<LinearLayout
android:layout_gravity="center_horizontal|center_vertical"
android:layout_margin="16dp"
android:orientation="vertical"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
<ImageButton
android:layout_width="122dp"
android:layout_height="141dp"
android:layout_gravity="center"
android:id="#+id/contactus"
android:src="#drawable/cont"/>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="CONTACT US"
android:textSize="20dp"
android:textColor="#ffff"
android:textStyle="bold"
android:textAppearance="#style/TextAppearance.AppCompat.Headline" />
</LinearLayout>
<LinearLayout
android:layout_gravity="center_horizontal|center_vertical"
android:layout_margin="16dp"
android:orientation="vertical"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
<ImageButton
android:layout_width="123dp"
android:layout_height="128dp"
android:onClick="onClick"
android:layout_gravity="center"
android:src="#drawable/vi"
android:id="#+id/visitus" />
<TextView
android:layout_width="wrap_content"
android:layout_height="48dp"
android:text="VISIT US"
android:gravity="bottom"
android:textAlignment="center"
android:textColor="#ffffff"
android:textStyle="bold"
android:textAppearance="#style/TextAppearance.AppCompat.Headline" />
</LinearLayout>
</GridLayout>
</LinearLayout>
when i run the app. it is running but when i click on any imagebutton the app keeps stopping. i cant understand the mistake i did .in image you can see my layout its running but imagebuttons are not working
please any one help me
thanks in advance

Try the below one,
package com.example.applincatio.t;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.webkit.WebChromeClient;
import android.webkit.WebView;
public class moddle extends AppCompatActivity {
String url;
WebView webView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
webView = (WebView) findViewById(R.id.web_link);
webView.clearCache(true);
webView.clearHistory();
webView.getSettings().setJavaScriptEnabled(true);
Intent intent = this.getIntent();
if (intent != null) {
Bundle data = getIntent().getExtras();
if (data.containsKey("webview")) {
url = data.getString("webview");
}
if (data.containsKey("webivewContact")) {
url = data.getString("webivewContact");
}
if (data.containsKey("webivewAbout")) {
url = data.getString("webivewAbout");
}
webView.setWebChromeClient(new WebChromeClient() {
public void onProgressChanged(WebView wView, int progress) {
// webViewActivity.setTitle("Loading...");
// webViewActivity.requestWindowFeature(progress * 100);
if(progress == 100) {
// webViewActivity.setTitle(R.string.app_name);
}
}
});
url = "https://moodle.kluniversity.in/login/index.php";
webView.loadUrl(url);
}
}
}
Thanks!

FATAL EXCEPTION: main....java.lang.RuntimeException: Unable to instantiate activity ComponentInfo.? [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 5 years ago.
I'm very new to Android Studio and I know a little java.So I'm trying a simple calculator app with simple layout.I hope all my code is correct but I don't know what's wrong in it.When I run the app it is not at all opening and showing a FATAL exception main.Here is the xml code,java code and logcat of my app.So please help me to make corrections.Thanks!
XML Code ::
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayoutxmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#color/colorPrimary"
tools:context="com.example.narendra.calculator.MainActivity"
tools:layout_editor_absoluteY="81dp"
tools:layout_editor_absoluteX="0dp">
<EditText
android:id="#+id/editText"
android:layout_width="360dp"
android:layout_height="159dp"
android:background="#android:color/holo_blue_light"
android:ems="10"
android:hint="#string/num"
android:inputType="number"
android:textAlignment="center"
android:textAllCaps="true"
android:textSize="50sp"
android:textStyle="bold"
tools:ignore="MissingConstraints,RtlHardcoded"
app:layout_constraintTop_toTopOf="parent"
android:layout_marginTop="16dp"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
android:layout_marginRight="8dp"
android:layout_marginLeft="8dp"
android:layout_marginStart="8dp"
android:layout_marginEnd="8dp" />
<EditText
android:id="#+id/editText2"
android:layout_width="360dp"
android:layout_height="159dp"
android:background="#android:color/holo_green_light"
android:ems="10"
android:hint="#string/Num2"
android:inputType="number"
android:textAlignment="center"
android:textAllCaps="true"
android:textSize="50sp"
android:textStyle="bold"
tools:ignore="MissingConstraints,RtlHardcoded"
tools:layout_editor_absoluteY="180dp"
tools:layout_editor_absoluteX="26dp" />
<Button
android:id="#+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="onAddButtonClick"
android:text="#string/a"
android:textSize="50sp"
app:layout_constraintLeft_toLeftOf="#+id/editText2"
app:layout_constraintTop_toTopOf="#+id/editText"
android:layout_marginTop="323dp"
tools:ignore="RtlHardcoded"
app:layout_constraintRight_toLeftOf="#+id/button3"
app:layout_constraintHorizontal_bias="0.0"
android:layout_marginRight="5dp"
android:layout_marginEnd="5dp" />
<Button
android:id="#+id/button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="onSubtractionButtonClick"
android:text="#string/m"
android:textSize="50sp"
android:layout_marginLeft="5dp"
app:layout_constraintTop_toTopOf="#+id/editText"
android:layout_marginTop="323dp"
tools:ignore="RtlHardcoded"
app:layout_constraintLeft_toRightOf="#+id/button"
app:layout_constraintHorizontal_bias="0.03"
android:layout_marginRight="5dp"
app:layout_constraintRight_toRightOf="#+id/button3"
android:layout_marginStart="5dp"
android:layout_marginEnd="5dp" />
<Button
android:id="#+id/button3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="onMultiplicationButtonClick"
android:text="#string/p"
android:textSize="50sp"
android:layout_marginLeft="5dp"
app:layout_constraintTop_toTopOf="#+id/editText"
android:layout_marginTop="323dp"
tools:ignore="RtlHardcoded"
app:layout_constraintLeft_toRightOf="#+id/button2"
android:layout_marginRight="5dp"
app:layout_constraintRight_toRightOf="#+id/button4"
app:layout_constraintHorizontal_bias="0.0"
android:layout_marginStart="5dp"
android:layout_marginEnd="5dp" />
<Button
android:id="#+id/button4"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="onDivisionButtonClick"
android:text="#string/d"
android:textSize="50sp"
android:layout_marginLeft="5dp"
app:layout_constraintRight_toRightOf="#+id/editText2"
app:layout_constraintTop_toTopOf="#+id/editText"
android:layout_marginTop="323dp"
tools:ignore="RtlHardcoded"
app:layout_constraintLeft_toRightOf="#+id/button3"
app:layout_constraintHorizontal_bias="0.0"
android:layout_marginStart="5dp"
android:layout_marginRight="5dp" />
<TextView
android:id="#+id/textView"
android:layout_width="360dp"
android:layout_height="100dp"
android:layout_marginBottom="8dp"
android:layout_marginLeft="8dp"
android:layout_marginRight="16dp"
android:layout_marginTop="8dp"
android:background="#color/colorAccent"
android:text="#string/Result"
android:textAlignment="center"
android:textAllCaps="true"
android:textSize="50sp"
android:textStyle="bold"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintHorizontal_bias="0.771"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="0.839"
tools:ignore="RtlHardcoded" />
Java Code ::
package com.example.narendra.calculator;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
EditText e1=(EditText)findViewById(R.id.editText);
EditText e2=(EditText)findViewById(R.id.editText2);
TextView t1=(TextView)findViewById(R.id.textView);
int num1=Integer.parseInt(e1.getText().toString());
int num2=Integer.parseInt(e2.getText().toString());
public void conditionCheck(){
if(e1.getText().toString().isEmpty()){
e1.setError("Please Enter a valid number");
}
else if(e2.getText().toString().isEmpty()){
e2.setError("Please Enter a valid number");
}
}
public void onAddButtonClick(View v){
conditionCheck();
int sum=num1+num2;
t1.setText(sum);
Toast.makeText(MainActivity.this, " Thank You ", Toast.LENGTH_SHORT).show();
}
public void onSubtractionButtonClick(View v){
conditionCheck();
int diff=num1-num2;
t1.setText(diff);
Toast.makeText(MainActivity.this, " Thank You ", Toast.LENGTH_SHORT).show();
}
public void onMultiplicationButtonClick(View v){
conditionCheck();
int product=num1*num2;
t1.setText(product);
Toast.makeText(MainActivity.this, " Thank You ", Toast.LENGTH_SHORT).show();
}
public void onDivisionButtonClick(View v){
conditionCheck();
if(num2==0){
e2.setError(" Zero is not allowed here");
}
else {
int quotient = num1 / num2;
t1.setText(quotient);
Toast.makeText(MainActivity.this, " Thank You ", Toast.LENGTH_SHORT).show();
}
}
}
Logcat ::
06-14 12:31:23.216 4822-4822/? I/art: Not late-enabling -Xcheck:jni (already on)
06-14 12:31:23.216 4822-4822/? W/art: Unexpected CPU variant for X86 using defaults: x86
06-14 12:31:23.342 4822-4822/? W/System: ClassLoader referenced unknown path: /data/app/com.example.narendra.calculator-2/lib/x86
06-14 12:31:23.348 4822-4822/? I/InstantRun: starting instant run server: is main process
06-14 12:31:23.405 4822-4822/? D/AndroidRuntime: Shutting down VM
06-14 12:31:23.405 4822-4822/? E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.narendra.calculator, PID: 4822
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.narendra.calculator/com.example.narendra.calculator.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2548)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
at android.support.v7.app.AppCompatDelegateImplBase.<init>(AppCompatDelegateImplBase.java:120)
at android.support.v7.app.AppCompatDelegateImplV9.<init>(AppCompatDelegateImplV9.java:155)
at android.support.v7.app.AppCompatDelegateImplV11.<init>(AppCompatDelegateImplV11.java:31)
at android.support.v7.app.AppCompatDelegateImplV14.<init>(AppCompatDelegateImplV14.java:55)
at android.support.v7.app.AppCompatDelegateImplV23.<init>(AppCompatDelegateImplV23.java:33)
at android.support.v7.app.AppCompatDelegateImplN.<init>(AppCompatDelegateImplN.java:33)
at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:201)
at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:185)
at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:519)
at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:190)
at com.example.narendra.calculator.MainActivity.<init>(MainActivity.java:17)
at java.lang.Class.newInstance(Native Method)
at android.app.Instrumentation.newActivity(Instrumentation.java:1078)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2538)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707) 
at android.app.ActivityThread.-wrap12(ActivityThread.java) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:154) 
at android.app.ActivityThread.main(ActivityThread.java:6077) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756) 

Your onCreate() is closed early
Change it to
package com.example.narendra.calculator;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
EditText e1,e2;
int num1,num2;
TextView t1;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
e1 = (EditText) findViewById(R.id.editText);
e2 = (EditText) findViewById(R.id.editText2);
t1 = (TextView) findViewById(R.id.textView);
num1 = Integer.parseInt(e1.getText().toString());
num2 = Integer.parseInt(e2.getText().toString());
} public void conditionCheck(){
if(e1.getText().toString().isEmpty()){
e1.setError("Please Enter a valid number");
}
else if(e2.getText().toString().isEmpty()){
e2.setError("Please Enter a valid number");
}
}
public void onAddButtonClick(View v){
conditionCheck();
int sum=num1+num2;
t1.setText(sum);
Toast.makeText(MainActivity.this, " Thank You ", Toast.LENGTH_SHORT).show();
}
public void onSubtractionButtonClick(View v){
conditionCheck();
int diff=num1-num2;
t1.setText(diff);
Toast.makeText(MainActivity.this, " Thank You ", Toast.LENGTH_SHORT).show();
}
public void onMultiplicationButtonClick(View v){
conditionCheck();
int product=num1*num2;
t1.setText(product);
Toast.makeText(MainActivity.this, " Thank You ", Toast.LENGTH_SHORT).show();
}
public void onDivisionButtonClick(View v){
conditionCheck();
if(num2==0){
e2.setError(" Zero is not allowed here");
}
else {
int quotient = num1 / num2;
t1.setText(quotient);
Toast.makeText(MainActivity.this, " Thank You ", Toast.LENGTH_SHORT).show();
}
}
}

Just modify the code of (view init) position,
like this:
MainActivity{
onCreate(){
View view = findViewById(id);
}
}
Note: the Activity is a component that has self life-cycle. so can't apply it as a simple Pojo