Command design pattern

README.md

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-# DesignPatternsJava9
-This repo consists Gang of Four Design patterns code on Java 9. Each branch in the repository has code of 1 design pattern. Switch repository to try out different design patterns.
+# What is Command Design Pattern 
+Command encapsulate all information needed to perform an action. It allows the requester of a particular action to be decoupled from the object that performs the action.
+
+## Diagram
+![Diagram](https://github.com/premaseem/DesignPatternsJava9/blob/command-pattern/diagrams/Command%20Design%20Pattern%20class%20diagram.jpeg "Diagram")
+
+![Diagram](https://github.com/premaseem/DesignPatternsJava9/blob/command-pattern/diagrams/Command-Design-Pattern-general%20-%20Page%201.png "Diagram")
+
+![Diagram](https://github.com/premaseem/DesignPatternsJava9/blob/command-pattern/diagrams/command%20sequence%20diagram.png "Diagram")
+
+### When to use Command Design Pattern 
+The invoker should be decoupled from the object handling the invocation.
+
+### Learn Design Patterns with Java by Aseem Jain
+This repository contains working project code used in video Course by Packt Publication with title "Learn Design Patterns with Java " authored by "Aseem Jain".
+
+### Course link: 
+https://www.packtpub.com/application-development/learn-design-patterns-java-9-video
+
+### ![ http://in.linkedin.com/in/premaseem](https://github.com/premaseem/DesignPatternsJava9/blob/master/linkedin.png "http://in.linkedin.com/in/premaseem") Profile:  http://in.linkedin.com/in/premaseem
+
+### Authors blog on design patterns:
+https://premaseem.wordpress.com/category/computers/design-patterns/
+
+### Software Design pattern community face book page:
+https://www.facebook.com/DesignPatternGuru/
+
+### Note: 
+* This code base will work on Java 9 and above versions. 
+* `diagrams` folders carry UML diagrams.
+* `pattern` folder has code of primary example. 
+* `patternBonus` folder has code of secondary or bonus example.

pattern/src/com/premaseem/Client.java

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 package com.premaseem;
 
+import java.util.Scanner;
+
 /*
 @author: Aseem Jain
 @title: Design Patterns with Java 9
 @link: https://premaseem.wordpress.com/category/computers/design-patterns/
-@copyright: 2018 Packt Publication
 */
 public class Client {
     public static void main (String[] args) {
-        System.out.println("Singleton cook example ");
+        Scanner scanInput = new Scanner(System.in);
+        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");
+        }
+        else if (command.equalsIgnoreCase("LightOff")){
+            System.out.println("Light turned off");
+        }
+        else {
+            System.out.println(command+ " Command not found");
+        }
+
+        // Lessons Learnt - BEFORE CODE
+        // Lots of if else ladder
+        // Commands cannot be added Dynamically
+        // Code is tightly coupled, no separation of responsibility
+        */
     }
 }

pattern/src/com/premaseem/Command.java

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+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();
+}

pattern/src/com/premaseem/CommandFactory.java

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+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;
+    }
+}

patternBonus/src/com/premaseem/commandPattern/ClientForRemoteControl.java

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+package com.premaseem.commandPattern;
+
+/*
+@author: Aseem Jain
+@title: Design Patterns with Java 9
+@link: https://premaseem.wordpress.com/category/computers/design-patterns/
+*/
+
+import java.util.Scanner;
+
+public class ClientForRemoteControl {
+
+	public static void main(String[] args) {
+		Scanner scan = new Scanner(System.in);
+		int repeatRunFlag = 1;
+		RemoteControl remote = new RemoteControl();
+		RemoteControlLoader loader = new RemoteControlLoader(remote);
+		loader.load();
+		while (repeatRunFlag == 1) {
+
+			System.out.println("This is the Client Main Command Pattern with Home Automation system ");
+
+			System.out.println("Loading the remote with approviate commands and mapping them in slots ... ");
+
+			System.out.println("Please press the any command between 0 to 10 for operation ");
+			System.out.println("Remember 11 is for Master off, \n 0 is for UNDO and \n 10 is undomacro mode");
+
+
+			int remoteButtonNumber = scan.nextInt();
+			remote.remoteButtonPress(remoteButtonNumber);
+
+			System.out.println("\n $$$$$$$$$$$$$$$$$$$$  Thanks by Prem Aseem $$$$$$$$$$$$$$$$$$$$$$ \n ");
+			System.out.println("Do you want to Re-run this program - Press 1 for yes and 0 or other digits to EXIT ");
+			try {
+				repeatRunFlag = scan.nextInt();
+			} catch (Exception e) {
+				repeatRunFlag = 0;
+			}
+		}
+	}
+}