Class PaymentActivity extends AppCompatActivity {
public static final String PAYPAL_CLIENT_ID = "YOUR_PAYPAL_CLIENT_ID";
public PaymentActivity()   // initialising paypal details 
{
  //Paypal Configuration Object
    private static PayPalConfiguration config = new PayPalConfiguration()
            // Start with mock environment.  When ready, switch to sandbox (ENVIRONMENT_SANDBOX)
            // or live (ENVIRONMENT_PRODUCTION)
            .environment(PayPalConfiguration.ENVIRONMENT_SANDBOX)
            .clientId(PayPalConfig.PAYPAL_CLIENT_ID)
}
private void getPayment() {
        //Getting the amount from editText
        paymentAmount = "50";  // amount in dollar
        //Creating a paypalpayment 
        PayPalPayment payment = new PayPalPayment(new BigDecimal(String.valueOf(paymentAmount)), "USD", "Product_Details",
                PayPalPayment.PAYMENT_INTENT_SALE);
        //Creating Paypal Payment activity intent 
        Intent intent = new Intent(this, PaymentActivity.class);
        //putting the paypal configuration to the intent 
        intent.putExtra(PayPalService.EXTRA_PAYPAL_CONFIGURATION, config);
         //Puting paypal payment to the intent 
        intent.putExtra(PaymentActivity.EXTRA_PAYMENT, payment);
         //Starting the intent activity for result
        //the request code will be used on the method onActivityResult 
        startActivityForResult(intent, PAYPAL_REQUEST_CODE);
    }
 @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        //If the result is from paypal 
        if (requestCode == PAYPAL_REQUEST_CODE) {
            //If the result is OK i.e. user has not canceled the payment 
            if (resultCode == Activity.RESULT_OK) {
                //Getting the payment confirmation 
                PaymentConfirmation confirm = data.getParcelableExtra(PaymentActivity.EXTRA_RESULT_CONFIRMATION);
                //if confirmation is not null 
                if (confirm != null) {
                    try {
                        //Getting the payment details 
                        String paymentDetails = confirm.toJSONObject().toString(4);
                        Log.i("paymentExample", paymentDetails);
                        //Starting a new activity for the payment details and also putting the payment details with intent 
                        startActivity(new Intent(this, ConfirmationActivity.class)
                                .putExtra("PaymentDetails", paymentDetails)
                                .putExtra("PaymentAmount", paymentAmount));
                    } catch (JSONException e) {
                        Log.e("paymentExample", "an extremely unlikely failure occurred: ", e);
                    }
                }
            } else if (resultCode == Activity.RESULT_CANCELED) {
                Log.i("paymentExample", "The user canceled.");
            } else if (resultCode == PaymentActivity.RESULT_EXTRAS_INVALID) {
                Log.i("paymentExample", "An invalid Payment or PayPalConfiguration was submitted. Please see the docs.");
            }
        }
    }
}