In-App Billing consumable product

public class MainActivity extends AppCompatActivity {
IabHelper mHelper;


boolean verifyDeveloperPayload(Purchase p) {
    String payload = p.getDeveloperPayload();


    /*
     * TODO: verify that the developer payload of the purchase is correct. It will be
     * the same one that you sent when initiating the purchase.
     *
     * WARNING: Locally generating a random string when starting a purchase and
     * verifying it here might seem like a good approach, but this will fail in the
     * case where the user purchases an item on one device and then uses your app on
     * a different device, because on the other device you will not have access to the
     * random string you originally generated.
     *
     * So a good developer payload has these characteristics:
     *
     * 1. If two different users purchase an item, the payload is different between them,
     *    so that one user's purchase can't be replayed to another user.
     *
     * 2. The payload must be such that you can verify it even when the app wasn't the
     *    one who initiated the purchase flow (so that items purchased by the user on
     *    one device work on other devices owned by the user).
     *
     * Using your own server to store and verify developer payloads across app
     * installations is recommended.
     */


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


    String base64EncodedPublicKey = "MY_KEY";


    // compute your public key and store it in base64EncodedPublicKey
    mHelper = new IabHelper(this, base64EncodedPublicKey);
    mHelper.enableDebugLogging(true);


    mHelper.startSetup(new IabHelper.OnIabSetupFinishedListener() {
        public void onIabSetupFinished(IabResult result) {
            if (!result.isSuccess()) {
                // Oh no, there was a problem.
                Log.d("TAG", "Problem setting up In-app Billing: " + result);
                Log.i("TAG", "ERROR");
            }
            // Hooray, IAB is fully set up!
            //check owned items & consum em
            checkOwnedItems();
            //make a test purchase
            makePurchase();
        }
    });


}


private void makePurchase() {
    try {
        mHelper.launchPurchaseFlow(this, "coins", 10001, mPurchaseFinishedListener, "kp");
    } catch (IabHelper.IabAsyncInProgressException e) {
        e.printStackTrace();
    }
}


private void checkOwnedItems() {
    try {
        mHelper.queryInventoryAsync(mGotInventoryListener);
    } catch (IabHelper.IabAsyncInProgressException e) {
        //complain("Error querying inventory. Another async operation in progress.");
    }
}




// Listener that's called when we finish querying the items and subscriptions we own
IabHelper.QueryInventoryFinishedListener mGotInventoryListener = new IabHelper.QueryInventoryFinishedListener() {
    public void onQueryInventoryFinished(IabResult result, Inventory inventory) {
        Purchase item = inventory.getPurchase("coins");
        if (item != null && verifyDeveloperPayload(item)) {
            //Log.d("TAG", "We have gas. Consuming it.");
            try {
                mHelper.consumeAsync(inventory.getPurchase("coins"), mConsumeFinishedListener);
            } catch (IabHelper.IabAsyncInProgressException e) {
                // complain("Error consuming gas. Another async operation in progress.");
            }
            return;
        }
    }


    };


// Called when consumption is complete
IabHelper.OnConsumeFinishedListener mConsumeFinishedListener = new IabHelper.OnConsumeFinishedListener() {
    public void onConsumeFinished(Purchase purchase, IabResult result) {
        Log.d("TAG", "Consumption finished. Purchase: " + purchase + ", result: " + result);


        // if we were disposed of in the meantime, quit.
        if (mHelper == null) return;


        // We know this is the "gas" sku because it's the only one we consume,
        // so we don't check which sku was consumed. If you have more than one
        // sku, you probably should check...
        if (result.isSuccess()) {
            // successfully consumed, so we apply the effects of the item in our
            // game world's logic, which in our case means filling the gas tank a bit
            //Log.d(TAG, "Consumption successful. Provisioning.");
            //mTank = mTank == TANK_MAX ? TANK_MAX : mTank + 1;
           // saveData();
           // alert("You filled 1/4 tank. Your tank is now " + String.valueOf(mTank) + "/4 full!");
        }
        else {
            //complain("Error while consuming: " + result);
        }
       Log.d("TAG", "End consumption flow.");
    }
};




// Callback for when a purchase is finished
IabHelper.OnIabPurchaseFinishedListener mPurchaseFinishedListener = new IabHelper.OnIabPurchaseFinishedListener() {
    public void onIabPurchaseFinished(IabResult result, Purchase purchase) {
        Log.d("TAG", "Purchase finished: " + result + ", purchase: " + purchase);


        // if we were disposed of in the meantime, quit.
        if (mHelper == null) return;


        if (result.isFailure()) {
           // complain("Error purchasing: " + result);
            return;
        }
        if (!verifyDeveloperPayload(purchase)) {
           // complain("Error purchasing. Authenticity verification failed.");
            return;
        }


        Log.d("TAG", "Purchase successful.");


        if (purchase.getSku().equals("coins")) {


            Log.d("TAG", "Purchase is gas. Starting gas consumption.");
            try {
                mHelper.consumeAsync(purchase, mConsumeFinishedListener);
            } catch (IabHelper.IabAsyncInProgressException e) {
                //complain("Error consuming gas. Another async operation in progress.");
                return;
            }
        }
    }
};


@Override
public void onDestroy() {
    super.onDestroy();
    if (mHelper != null) try {
        mHelper.dispose();
    } catch (IabHelper.IabAsyncInProgressException e) {
        e.printStackTrace();
    }
    mHelper = null;
}
}