Up Button Tutorial

Activity2.java

package com.example.application.upbuttonexample;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class Activity2 extends AppCompatActivity {
    private Button button2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_2);

        getSupportActionBar().setTitle("Activity 2");
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        button2 = (Button) findViewById(R.id.button2);
        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                openActivity3();
            }
        });
    }

    public void openActivity3() {
        Intent intent = new Intent(this, Activity3.class);
        startActivity(intent);
    }
}

Activity3.java

package com.example.application.upbuttonexample;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class Activity3 extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_3);

        getSupportActionBar().setTitle("Activity 3");
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    }
}

activity_2.xml

<?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"
    tools:context="com.example.application.upbuttonexample.Activity2">

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:text="open activity 3" />

</RelativeLayout>

activity_3.xml

<?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"
    tools:context="com.example.application.upbuttonexample.Activity3">

</RelativeLayout>

activity_main.xml

<?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"
    tools:context="com.example.application.upbuttonexample.MainActivity">

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:text="open activity 2" />

</RelativeLayout>

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.application.upbuttonexample">

    <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>
        <activity
            android:name=".Activity2"
            android:parentActivityName=".MainActivity"></activity>
        <activity
            android:name=".Activity3"
            android:parentActivityName=".Activity2"></activity>
    </application>

</manifest>

MainActivity.java

package com.example.application.upbuttonexample;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {
    private Button button;

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

        button = (Button) findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                openActivity2();
            }
        });
    }

    public void openActivity2() {
        Intent intent = new Intent(this, Activity2.class);
        startActivity(intent);
    }
}

getSupportActionBar().setTitle("Activity 2");
getSupportActionBar().setDisplayHomeAsUpEnabled(true);

Either of these lines crashes Android Studio. I've tried other video to create an ActionBar. Can we see how you create the Action Bar?

It appears to me that the ActionBar or a Lib is missing and this is why the app crashes. Please come back to help.

Will using
import androidx.appcompat.app.AppCompatActivity;
rather than
import android.support.v7.app.AppCompatActivity

cause my app to crash when using getSupportActionBar().setTitle("Activity 2"); or
getSupportActionBar().setDisplayHomeAsUpEnabled(true);

I've been unable to get this code to stop crashing?