update:demo4

com/study/demo4/HomeAppliance.java

@@ -0,0 +1,26 @@
+package com.study.demo4;
+
+abstract class HomeAppliance implements SmartDevice {
+  protected String name;
+  protected boolean isOn;
+
+  public HomeAppliance(String name) {
+    this.name = name;
+    this.isOn = false;
+  }
+
+  @Override
+  public void turnOn() {
+    isOn = true;
+  }
+
+  @Override
+  public void turnOff() {
+    isOn = false;
+  }
+
+  @Override
+  public String getStatus() {
+    return name + " is " + (isOn ? "ON" : "OFF");
+  }
+}