How can create java class in unity, using android studio,

import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

import com.razorpay.Checkout;
import com.razorpay.PaymentResultListener;

import org.json.JSONObject;

public class PaymentActivity extends Activity implements PaymentResultListener {
private static final String TAG = PaymentActivity.class.getSimpleName();

@override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);

setContentView(R.layout.activity_payment);

/*
To ensure faster loading of the Checkout form,
call this method as early as possible in your checkout flow.
*/
Checkout.preload(getApplicationContext());

// Payment button created by you in XML layout
Button button = (Button) findViewById(R.id.btn_pay);

button.setOnClickListener(new View.OnClickListener() {
@override
public void onClick(View v) {
startPayment();
}
});
}

public void startPayment() {
/*
You need to pass current activity in order to let Razorpay create CheckoutActivity
*/
final Activity activity = this;

final Checkout co = new Checkout();

try {
JSONObject options = new JSONObject();
options.put("name", "Razorpay Corp");
options.put("description", "Demoing Charges");
//You can omit the image option to fetch the image from dashboard
options.put("image", "https://s3.amazonaws.com/rzp-mobile/images/rzp.png");
options.put("currency", "INR");
options.put("amount", "100");

JSONObject preFill = new JSONObject();
preFill.put("email", "test@razorpay.com");
preFill.put("contact", "9876543210");

options.put("prefill", preFill);

co.open(activity, options);
} catch (Exception e) {
Toast.makeText(activity, "Error in payment: " + e.getMessage(), Toast.LENGTH_SHORT)
.show();
e.printStackTrace();
}
}

/**
* The name of the function has to be
* onPaymentSuccess
* Wrap your code in try catch, as shown, to ensure that this method runs correctly
*/
@SuppressWarnings("unused")
@override
public void onPaymentSuccess(String razorpayPaymentID) {
try {
Toast.makeText(this, "Payment Successful: " + razorpayPaymentID, Toast.LENGTH_SHORT).show();
} catch (Exception e) {
Log.e(TAG, "Exception in onPaymentSuccess", e);
}
}

/**
* The name of the function has to be
* onPaymentError
* Wrap your code in try catch, as shown, to ensure that this method runs correctly
*/
@SuppressWarnings("unused")
@override
public void onPaymentError(int code, String response) {
try {
Toast.makeText(this, "Payment failed: " + code + " " + response, Toast.LENGTH_SHORT).show();
} catch (Exception e) {
Log.e(TAG, "Exception in onPaymentError", e);
}
}
}