this code open whatsapp to send message direct from your app to whatsapp (^_^)

Open WhatsApp Messaging

String number = "+970598074212"
/////////////////////////////////////////////////////////////
btn_send_message_whatsapp.setOnClickListener(v -> {
            onClickWhatsApp("970598074212");// hint without + 
            // if the number with + like +970598074212
            //using 
            //onClickWhatsApp(number.substring(1));
        });

///////////////////////Open Whatsapp////////////////////////
private void onClickWhatsApp(String phone) {
        try {      
            Intent sendIntent = new Intent("android.intent.action.MAIN");
            sendIntent.setComponent(new ComponentName("com.whatsapp", "com.whatsapp.Conversation"));
            sendIntent.putExtra("jid", PhoneNumberUtils.stripSeparators(phone) + "@s.whatsapp.net");
            startActivity(sendIntent);
        } catch (Exception e) {
            Toast.makeText(activity, getString(R.string.whatsapp_not_install), Toast.LENGTH_SHORT).show();
        }
    }