建議你開始 migrate 到 kotlin ，它會增加你寫 code 的效率的。Java code 大概是長這樣。

if(billingDataSource != null && billingDataSource.isPurchased("IN_APP_SKU_1") != null) {

billingDataSource.isPurchased.observe(this, (purchased) -> {

if(purchased) {

textView.setText("Purchased");

button.isEnabled(false);

} else {

textView.setText("Not purchased");

button.isEnabled(true);

}

})

}

if(billingDataSource!=null && billing.observeNewPurchases()!=null) {

billingDataSource.observeNewPurchase().observe(this, (skus)-> {

for(String sku: skus) {

Log.d("DEBUG", "New purchase on sku:"+sku);

}

})

}