Why is the application crashing?

Question

Android

I am building an application according to the manual. Launch fails

package com.djamali.bolh;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.KeyEvent;
import android.webkit.WebSettings;
import android.webkit.WebView;

public class MainActivity extends AppCompatActivity {

    private WebView webView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //setContentView(R.layout.activity_main);

        WebView webView = (WebView) findViewById(R.id.webView);

        WebSettings webSettings = webView.getSettings();
        webSettings.setJavaScriptEnabled(true);

        webView.loadUrl("https://javadevblog.com");

    }

    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if ((keyCode == KeyEvent.KEYCODE_BACK) && this.webView.canGoBack()) {
            this.webView.goBack();
            return true;
        }

        return super.onKeyDown(keyCode, event);
    }
}

package com.djamali.bolh;

import android.app.Activity;
import android.content.Intent;
import android.net.Uri;
import android.webkit.WebView;
import android.webkit.WebViewClient;

public class SimpleWebViewClientImpl extends WebViewClient {
    private Activity activity = null;

    public SimpleWebViewClientImpl(Activity activity) {
        this.activity = activity;
    }

    @Override
    public boolean shouldOverrideUrlLoading(WebView webView, String url) {
        // все ссылки, в которых содержится 'javadevblog.com'
        // будут открываться внутри приложения
        if (url.contains("javadevblog.com")) {
            return false;
        }
        // все остальные ссылки будут спрашивать какой браузер открывать
        Intent intent = new Intent(Intent.ACTION_VIEW, Uri.parse(url));
        activity.startActivity(intent);
        return true;
    }
}

<?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=".MainActivity"
    android:theme="@style/Theme.AppCompat.NoActionBar">

    <WebView
        android:id="@+id/webView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true" />

</android.support.constraint.ConstraintLayout>

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

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

</manifest>

Answer 1

setContentView()uncomment.