Use entity class vars in Switch demo (#51906)

* Use entity class vars in Switch demo

* Fix missing initial state of the demo switch

homeassistant/components/demo/switch.py

@@ -1,4 +1,6 @@
 """Demo platform that has two fake switches."""
+from __future__ import annotations
+
 from homeassistant.components.switch import SwitchEntity
 from homeassistant.const import DEVICE_DEFAULT_NAME
 
@@ -9,9 +11,9 @@ async def async_setup_platform(hass, config, async_add_entities, discovery_info=
     """Set up the demo switches."""
     async_add_entities(
         [
-            DemoSwitch("swith1", "Decorative Lights", True, None, True),
+            DemoSwitch("switch1", "Decorative Lights", True, None, True),
             DemoSwitch(
-                "swith2",
+                "switch2",
                 "AC",
                 False,
                 "mdi:air-conditioner",
@@ -30,78 +32,42 @@ async def async_setup_entry(hass, config_entry, async_add_entities):
 class DemoSwitch(SwitchEntity):
     """Representation of a demo switch."""
 
-    def __init__(self, unique_id, name, state, icon, assumed, device_class=None):
+    _attr_should_poll = False
+
+    def __init__(
+        self,
+        unique_id: str,
+        name: str,
+        state: bool,
+        icon: str | None,
+        assumed: bool,
+        device_class: str | None = None,
+    ) -> None:
         """Initialize the Demo switch."""
-        self._unique_id = unique_id
-        self._name = name or DEVICE_DEFAULT_NAME
-        self._state = state
-        self._icon = icon
-        self._assumed = assumed
-        self._device_class = device_class
+        self._attr_assumed_state = assumed
+        self._attr_device_class = device_class
+        self._attr_icon = icon
+        self._attr_is_on = state
+        self._attr_name = name or DEVICE_DEFAULT_NAME
+        self._attr_today_energy_kwh = 15
+        self._attr_unique_id = unique_id
 
     @property
     def device_info(self):
         """Return device info."""
         return {
-            "identifiers": {
-                # Serial numbers are unique identifiers within a specific domain
-                (DOMAIN, self.unique_id)
-            },
+            "identifiers": {(DOMAIN, self.unique_id)},
             "name": self.name,
         }
 
-    @property
-    def unique_id(self):
-        """Return the unique id."""
-        return self._unique_id
-
-    @property
-    def should_poll(self):
-        """No polling needed for a demo switch."""
-        return False
-
-    @property
-    def name(self):
-        """Return the name of the device if any."""
-        return self._name
-
-    @property
-    def icon(self):
-        """Return the icon to use for device if any."""
-        return self._icon
-
-    @property
-    def assumed_state(self):
-        """Return if the state is based on assumptions."""
-        return self._assumed
-
-    @property
-    def current_power_w(self):
-        """Return the current power usage in W."""
-        if self._state:
-            return 100
-
-    @property
-    def today_energy_kwh(self):
-        """Return the today total energy usage in kWh."""
-        return 15
-
-    @property
-    def is_on(self):
-        """Return true if switch is on."""
-        return self._state
-
-    @property
-    def device_class(self):
-        """Return device of entity."""
-        return self._device_class
-
     def turn_on(self, **kwargs):
         """Turn the switch on."""
-        self._state = True
+        self._attr_is_on = True
+        self._attr_current_power_w = 100
         self.schedule_update_ha_state()
 
     def turn_off(self, **kwargs):
         """Turn the device off."""
-        self._state = False
+        self._attr_is_on = False
+        self._attr_current_power_w = 0
         self.schedule_update_ha_state()