#95 Updated and clarified Command pattern example

README.md

@@ -299,7 +299,7 @@ A programming idiom is a means of expressing a recurring construct in one or mor
 ## <a name="command">Command</a> [&#8593;](#list-of-design-patterns)
 **Intent:** Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations.
 
-![alt text](https://github.com/iluwatar/java-design-patterns/blob/master/command/etc/command_1.png "Command")
+![alt text](https://github.com/iluwatar/java-design-patterns/blob/master/command/etc/command.png "Command")
 
 **Applicability:** Use the Command pattern when you want to
 

command/etc/command.ucls

@@ -3,7 +3,7 @@
   realizations="true" associations="true" dependencies="false" nesting-relationships="true">  
   <class id="1" language="java" name="com.iluwatar.command.ShrinkSpell" project="command" 
     file="/command/src/main/java/com/iluwatar/command/ShrinkSpell.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="160" width="141" x="-171" y="634"/>    
+    <position height="178" width="141" x="-30" y="681"/>    
     <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
       sort-features="false" accessors="true" visibility="true">      
       <attributes public="true" package="true" protected="true" private="true" static="true"/>      
@@ -12,7 +12,7 @@
   </class>  
   <class id="2" language="java" name="com.iluwatar.command.Goblin" project="command" 
     file="/command/src/main/java/com/iluwatar/command/Goblin.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="106" width="138" x="13" y="1069"/>    
+    <position height="-1" width="-1" x="129" y="1223"/>    
     <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
       sort-features="false" accessors="true" visibility="true">      
       <attributes public="true" package="true" protected="true" private="true" static="true"/>      
@@ -21,7 +21,7 @@
   </class>  
   <class id="3" language="java" name="com.iluwatar.command.Wizard" project="command" 
     file="/command/src/main/java/com/iluwatar/command/Wizard.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="160" width="212" x="91" y="235"/>    
+    <position height="-1" width="-1" x="129" y="362"/>    
     <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
       sort-features="false" accessors="true" visibility="true">      
       <attributes public="true" package="true" protected="true" private="true" static="true"/>      
@@ -30,7 +30,7 @@
   </class>  
   <class id="4" language="java" name="com.iluwatar.command.Command" project="command" 
     file="/command/src/main/java/com/iluwatar/command/Command.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="159" width="142" x="9" y="435"/>    
+    <position height="-1" width="-1" x="129" y="561"/>    
     <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
       sort-features="false" accessors="true" visibility="true">      
       <attributes public="true" package="true" protected="true" private="true" static="true"/>      
@@ -39,66 +39,58 @@
   </class>  
   <class id="5" language="java" name="com.iluwatar.command.InvisibilitySpell" project="command" 
     file="/command/src/main/java/com/iluwatar/command/InvisibilitySpell.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="160" width="141" x="10" y="634"/>    
+    <position height="160" width="141" x="151" y="681"/>    
     <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
       sort-features="false" accessors="true" visibility="true">      
       <attributes public="true" package="true" protected="true" private="true" static="true"/>      
       <operations public="true" package="true" protected="true" private="true" static="true"/>    
     </display>  
   </class>  
-  <enumeration id="6" language="java" name="com.iluwatar.command.Visibility" project="command" 
+  <class id="6" language="java" name="com.iluwatar.command.Target" project="command" 
-    file="/command/src/main/java/com/iluwatar/command/Visibility.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="178" width="157" x="191" y="1069"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </enumeration>  
-  <enumeration id="7" language="java" name="com.iluwatar.command.Size" project="command" 
-    file="/command/src/main/java/com/iluwatar/command/Size.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="196" width="144" x="-171" y="1069"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </enumeration>  
-  <class id="8" language="java" name="com.iluwatar.command.Target" project="command" 
     file="/command/src/main/java/com/iluwatar/command/Target.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="195" width="176" x="13" y="834"/>    
+    <position height="-1" width="-1" x="129" y="1014"/>    
     <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
       sort-features="false" accessors="true" visibility="true">      
       <attributes public="true" package="true" protected="true" private="true" static="true"/>      
       <operations public="true" package="true" protected="true" private="true" static="true"/>    
     </display>  
   </class>  
-  <association id="9">    
+  <association id="7">    
-    <end type="SOURCE" refId="1" navigable="false">      
+    <end type="SOURCE" refId="3" navigable="false">      
-      <attribute id="10" name="target"/>      
+      <attribute id="8" name="redoStack">        
-      <multiplicity id="11" minimum="0" maximum="1"/>    
+        <position height="20" width="67" x="140" y="451"/>      
+      </attribute>      
+      <multiplicity id="9" minimum="0" maximum="2147483647">        
+        <position height="18" width="25" x="221" y="452"/>      
+      </multiplicity>    
     </end>    
-    <end type="TARGET" refId="8" navigable="true"/>    
+    <end type="TARGET" refId="4" navigable="true"/>    
     <display labels="true" multiplicity="true"/>  
   </association>  
-  <generalization id="12">    
+  <generalization id="10">    
+    <end type="SOURCE" refId="2"/>    
+    <end type="TARGET" refId="6"/>  
+  </generalization>  
+  <association id="11">    
+    <end type="SOURCE" refId="1" navigable="false">      
+      <attribute id="12" name="target"/>      
+      <multiplicity id="13" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="6" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <generalization id="14">    
     <end type="SOURCE" refId="1"/>    
     <end type="TARGET" refId="4"/>  
   </generalization>  
-  <generalization id="13">    
-    <bendpoint x="181" y="435"/>    
-    <bendpoint x="181" y="634"/>    
-    <end type="SOURCE" refId="3"/>    
-    <end type="TARGET" refId="8"/>  
-  </generalization>  
-  <generalization id="14">    
-    <end type="SOURCE" refId="2"/>    
-    <end type="TARGET" refId="8"/>  
-  </generalization>  
   <association id="15">    
     <end type="SOURCE" refId="3" navigable="false">      
-      <attribute id="16" name="undoStack"/>      
+      <attribute id="16" name="undoStack">        
-      <multiplicity id="17" minimum="0" maximum="2147483647"/>    
+        <position height="20" width="70" x="-17" y="451"/>      
+      </attribute>      
+      <multiplicity id="17" minimum="0" maximum="2147483647">        
+        <position height="18" width="25" x="60" y="452"/>      
+      </multiplicity>    
     </end>    
     <end type="TARGET" refId="4" navigable="true"/>    
     <display labels="true" multiplicity="true"/>  
@@ -112,42 +104,9 @@
       <attribute id="20" name="target"/>      
       <multiplicity id="21" minimum="0" maximum="1"/>    
     </end>    
-    <end type="TARGET" refId="8" navigable="true"/>    
-    <display labels="true" multiplicity="true"/>  
-  </association>  
-  <association id="22">    
-    <end type="SOURCE" refId="8" navigable="false">      
-      <attribute id="23" name="visibility"/>      
-      <multiplicity id="24" minimum="0" maximum="1"/>    
-    </end>    
     <end type="TARGET" refId="6" navigable="true"/>    
     <display labels="true" multiplicity="true"/>  
   </association>  
-  <association id="25">    
-    <end type="SOURCE" refId="8" navigable="false">      
-      <attribute id="26" name="size"/>      
-      <multiplicity id="27" minimum="0" maximum="1"/>    
-    </end>    
-    <end type="TARGET" refId="7" navigable="true"/>    
-    <display labels="true" multiplicity="true"/>  
-  </association>  
-  <association id="28">    
-    <end type="SOURCE" refId="3" navigable="false">      
-      <attribute id="29" name="redoStack"/>      
-      <multiplicity id="30" minimum="0" maximum="2147483647"/>    
-    </end>    
-    <end type="TARGET" refId="4" navigable="true"/>    
-    <display labels="true" multiplicity="true"/>  
-  </association>  
-  <association id="31">    
-    <bendpoint x="-162" y="834"/>    
-    <end type="SOURCE" refId="1" navigable="false">      
-      <attribute id="32" name="oldSize"/>      
-      <multiplicity id="33" minimum="0" maximum="1"/>    
-    </end>    
-    <end type="TARGET" refId="7" navigable="true"/>    
-    <display labels="true" multiplicity="true"/>  
-  </association>  
   <classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
     sort-features="false" accessors="true" visibility="true">    
     <attributes public="true" package="true" protected="true" private="true" static="true"/>    

command/src/main/java/com/iluwatar/command/App.java

@@ -4,7 +4,18 @@ package com.iluwatar.command;
  * 
  * In Command pattern actions are objects that can be executed and undone. 
  *
- * In this example the commands are the spells cast by the wizard on the goblin.
+ * Four terms always associated with the command pattern are command, receiver, invoker and client. A command 
+ * object (spell) knows about receiver (target) and invokes a method of the receiver. Values for parameters of 
+ * the receiver method are stored in the command. The receiver then does the work. An invoker object (wizard) 
+ * knows how to execute a command, and optionally does bookkeeping about the command execution. The invoker 
+ * does not know anything about a concrete command, it knows only about command interface. Both an invoker object 
+ * and several command objects are held by a client object (app). The client decides which commands to execute at 
+ * which points. To execute a command, it passes the command object to the invoker object.
+ * 
+ * In other words, in this example the wizard casts spells on the goblin. The wizard keeps track of the previous
+ * spells cast, so it is easy to undo them. In addition, the wizard keeps track of the spells undone, so they
+ * can be redone.
+ * 
  * 
  */
 public class App {

command/src/main/java/com/iluwatar/command/Goblin.java

@@ -1,5 +1,10 @@
 package com.iluwatar.command;
 
+/**
+ * 
+ * Goblin is the target of the spells
+ *
+ */
 public class Goblin extends Target {
 
 	public Goblin() {

command/src/main/java/com/iluwatar/command/InvisibilitySpell.java

@@ -1,5 +1,10 @@
 package com.iluwatar.command;
 
+/**
+ * 
+ * InvisibilitySpell is a concrete command
+ *
+ */
 public class InvisibilitySpell extends Command {
 
 	private Target target;

command/src/main/java/com/iluwatar/command/ShrinkSpell.java

@@ -1,5 +1,10 @@
 package com.iluwatar.command;
 
+/**
+ * 
+ * ShrinkSpell is a concrete command
+ *
+ */
 public class ShrinkSpell extends Command {
 
 	private Size oldSize;

command/src/main/java/com/iluwatar/command/Wizard.java

@@ -3,14 +3,17 @@ package com.iluwatar.command;
 import java.util.Deque;
 import java.util.LinkedList;
 
-public class Wizard extends Target {
+/**
+ * 
+ * Wizard is the invoker of the commands
+ *
+ */
+public class Wizard {
 
 	private Deque<Command> undoStack = new LinkedList<>();
 	private Deque<Command> redoStack = new LinkedList<>();
 
 	public Wizard() {
-		setSize(Size.NORMAL);
-		setVisibility(Visibility.VISIBLE);
 	}
 
 	public void castSpell(Command command, Target target) {
@@ -41,5 +44,4 @@ public class Wizard extends Target {
 	public String toString() {
 		return "Wizard";
 	}
-
 }