Command design pattern - AFTER CODE - Light switch project

premaseem · premaseem · commit d2afa805cc0f · 2018-03-05T19:13:37.000-06:00
Loose coupling and commands can be added dynamically with almost zero code changes in client file
diff --git a/pattern/src/com/premaseem/Client.java b/pattern/src/com/premaseem/Client.java
@@ -10,10 +10,31 @@
 public class Client {
     public static void main (String[] args) {
         Scanner scanInput = new Scanner(System.in);
-        System.out.println("Command Pattern Light switch project ");
-        System.out.println("Master - what command you want to execute ");
-        String command = scanInput.next();
+        System.out.println("Light switch Project using COMMAND DESIGN PATTERN \n ");
 
+       /** After implementing Command design pattern **/
+
+       // All available Commands will be created and init by command factory
+       CommandFactory cf = CommandFactory.init();
+
+       // Will list all commands which can be executed
+       cf.listCommands();
+
+       // Commands can be added and listed dynamically with ZERO code changes in client side
+       System.out.println("Master - what command you want to execute ");
+       String command = scanInput.next();
+
+       // Actual execution of command will happen
+       cf.executeCommand(command);
+
+        /** Lessons Learnt - AFTER CODE
+         # New commands can be added dynamically with ease
+         # Client is loosely coupled and have no knowledge of encapsulated commands
+         # Zero code changed needed at client when new commands are added
+         */
+
+
+       /** BEFORE CODE
         // Assume you will invoke a method to execute turn on method
         if (command.equalsIgnoreCase("LightOn")){
             System.out.println("Light turned on");
@@ -29,5 +50,6 @@ else if (command.equalsIgnoreCase("LightOff")){
         // Lots of if else ladder
         // Commands cannot be added Dynamically
         // Code is tightly coupled, no separation of responsibility
+        */
     }
 }
diff --git a/pattern/src/com/premaseem/Command.java b/pattern/src/com/premaseem/Command.java
@@ -0,0 +1,14 @@
+package com.premaseem;
+
+/*
+@author: Aseem Jain
+@title: Design Patterns with Java 9
+@link: https://premaseem.wordpress.com/category/computers/design-patterns/
+*/
+/**
+ * The Command functional interface.
+ */
+@FunctionalInterface
+public interface Command {
+    public void execute();
+}
diff --git a/pattern/src/com/premaseem/CommandFactory.java b/pattern/src/com/premaseem/CommandFactory.java
@@ -0,0 +1,47 @@
+package com.premaseem;
+
+/*
+@author: Aseem Jain
+@title: Design Patterns with Java 9
+@link: https://premaseem.wordpress.com/category/computers/design-patterns/
+*/
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+public final class CommandFactory {
+    private final Map<String, Command> commands;
+
+    private CommandFactory() {
+        commands = new HashMap<>();
+    }
+
+    public void addCommand(final String name, final Command command) {
+        commands.put(name, command);
+    }
+
+    public void executeCommand(String name) {
+        if (commands.containsKey(name)) {
+            commands.get(name).execute();
+        }else{
+            System.out.println(name+ " Command not found");
+        }
+    }
+
+    public void listCommands() {
+        System.out.println("Available commands: " + commands.keySet().stream().collect(Collectors.joining(", ")));
+    }
+
+    /* Factory pattern */
+    public static CommandFactory init() {
+        final CommandFactory cf = new CommandFactory();
+
+        // commands are added here using lambdas.
+        // It is also possible to dynamically add commands without editing the code.
+        cf.addCommand("LightOn", () -> System.out.println("Light turned on"));
+        cf.addCommand("LightOff", () -> System.out.println("Light turned off"));
+
+        return cf;
+    }
+}
