facebook login button implementation

Question

After implementing the login button this appears as an error

 E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: com.foksart.fixawyBeta, PID: 2773
                  java.lang.RuntimeException: Unable to start activity ComponentInfo{com.foksart.fixawyBeta/com.foksart.fixawyBeta.LoginActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.facebook.login.widget.LoginButton.setReadPermissions(java.lang.String[])' on a null object reference
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
                      at android.app.ActivityThread.-wrap11(ActivityThread.java)
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
                      at android.os.Handler.dispatchMessage(Handler.java:102)
                      at android.os.Looper.loop(Looper.java:148)
                      at android.app.ActivityThread.main(ActivityThread.java:5417)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                   Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.facebook.login.widget.LoginButton.setReadPermissions(java.lang.String[])' on a null object reference
                      at com.foksart.fixawyBeta.LoginActivity.onCreate(LoginActivity.java:75)
                      at android.app.Activity.performCreate(Activity.java:6237)
                      at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
                      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
                      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
                      at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
                      at android.os.Handler.dispatchMessage(Handler.java:102) 
                      at android.os.Looper.loop(Looper.java:148) 
                      at android.app.ActivityThread.main(ActivityThread.java:5417) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 

and my android manifest code is

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.foksart.fixawyBeta">
    <uses-permission android:name="android.permission.INTERNET"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme.NoActionBar">


        <meta-data android:name="com.facebook.sdk.ApplicationId" android:value="@string/facebook_app_id"/>
        <activity android:name=".MainActivity">
        </activity>

        <activity
            android:name="com.facebook.CustomTabActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.VIEW" />
                <category android:name="android.intent.category.DEFAULT" />
               <category android:name="android.intent.category.BROWSABLE" />
                <data android:scheme="@string/fb_login_protocol_scheme" />
            </intent-filter>
        </activity>
        <activity android:name=".LoginActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <activity android:name="com.facebook.FacebookActivity"
        android:configChanges=
        "keyboard|keyboardHidden|screenLayout|screenSize|orientation"
        android:label="@string/app_name" />
        <provider android:authorities="com.facebook.app.FacebookContentProvider1796817573897293"
        android:name="com.facebook.FacebookContentProvider"
        android:exported="true"/>
    </application>

</manifest>

and my activity.xml code is this

<android.support.design.widget.CoordinatorLayout
    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:id="@+id/content_login_page"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/bg"
    android:fitsSystemWindows="true"
    tools:context="com.foksart.fixawyBeta.LoginActivity"
    tools:showIn="@layout/activity_login_page">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">
<com.facebook.login.widget.LoginButton
            android:id="@+id/login_button"
            android:layout_width="80dp"
            android:layout_height="32dp"
            android:layout_below="@id/facebookTxt"
            android:layout_centerHorizontal="true"
            android:layout_marginTop="10dp"
            android:background="@drawable/facebookbtn"
            android:text="@string/facebook_btn"
            android:textColor="#ffffff"
            android:textSize="18sp"/>
</RelativeLayout>
</android.support.design.widget.CoordinatorLayout>

activity.java code

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.LinearLayout;
import com.facebook.CallbackManager;
import com.facebook.FacebookSdk;
import com.facebook.appevents.AppEventsLogger;
import com.facebook.login.widget.LoginButton;
import android.widget.Button;
import com.facebook.AccessToken;
import com.facebook.FacebookCallback;
import com.facebook.FacebookException;
import com.facebook.GraphRequest;
import com.facebook.GraphResponse;
import com.facebook.login.LoginResult;
import org.json.JSONException;
import org.json.JSONObject;
public class LoginActivity extends  AppCompatActivity   {
    private LinearLayout registrationForm;
    private ImageView collapseForm;
    private BottomSheetBehavior myBottomSheetBehavior;
    CallbackManager callbackManager;
    Button share,details;
    ShareDialog shareDialog;
    LoginButton login;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login_page);  
        FacebookSdk.sdkInitialize(getApplicationContext());
        AppEventsLogger.activateApp(getApplication());
        callbackManager = CallbackManager.Factory.create();
        login = (LoginButton)findViewById(R.id.login_button);
        login.setReadPermissions("public_profile email");
    }
}

i don't know what is going on and i am stuck for a while , i followed the documentation for facebook login implementation