Screen Orientation.

 MainActivity -

package com.example.screenorientation;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

    }

}

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activity_main -

<?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:gravity="center"

    tools:context=".MainActivity">

    <TextView

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:text="Welcome to Android Studio"

        android:textSize="45sp"

        android:textColor="#ff00"

        android:layout_gravity="center"

        />

    <Button

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="Hit Me"

         android:layout_marginTop="45dp"

        />

</LinearLayout>

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AndroidManifest -

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

    package="com.example.screenorientation">

    <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"

            android:screenOrientation="portrait">

            <intent-filter>

                <action android:name="android.intent.action.MAIN" />

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

            </intent-filter>

        </activity>

    </application>

</manifest>