Create QR Code Android Java example

Step 1: Add Build.gradle dependencies

implementation 'com.journeyapps:zxing-android-embedded:4.3.0'
implementation 'com.google.zxing:core:3.3.3'

Step 2: Uses-permission Camera in manifest

<uses-permission android:name="android.permission.CAMERA"/>
<uses-feature android:name="android.hardware.camera"/>

Step 3: MainActivity

package com.grt.qrcodescanninginanandroid;

import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;

import com.google.zxing.integration.android.IntentIntegrator;
import com.google.zxing.integration.android.IntentResult;

public class MainActivity extends AppCompatActivity {

    private Button scanQrButton;

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

        scanQrButton = findViewById(R.id.btn_scan_qr);

        scanQrButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                new IntentIntegrator(MainActivity.this).initiateScan();
            }
        });
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);


        IntentResult result = IntentIntegrator.parseActivityResult(requestCode, resultCode, data);
        if (result != null) {
            if (result.getContents() == null) {
                Toast.makeText(this, "Scan Cancelled", Toast.LENGTH_SHORT).show();
            } else {
                Toast.makeText(this, "Scanned: " + result.getContents(), Toast.LENGTH_LONG).show();
            }
        } else {
            super.onActivityResult(requestCode, resultCode, data);
        }
    }
}

Step 5: Xml 

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <LinearLayout
        
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        android:gravity="center"
        android:padding="16dp">

        <Button
            android:id="@+id/btn_scan_qr"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Scan QR Code"/>
    </LinearLayout>


</androidx.constraintlayout.widget.ConstraintLayout>

Output: