Merge pull request #1531 from ravening/command-functional

Refactor the command pattern to use lambda functions

command/README.md

@@ -48,18 +48,16 @@ public class Wizard {
 
   public Wizard() {}
 
-  public void castSpell(Command command, Target target) {
+  public void castSpell(Runnable runnable) {
-    LOGGER.info("{} casts {} at {}", this, command, target);
+    runnable.run();
-    command.execute(target);
+    undoStack.offerLast(runnable);
-    undoStack.offerLast(command);
   }
 
   public void undoLastSpell() {
     if (!undoStack.isEmpty()) {
       var previousSpell = undoStack.pollLast();
       redoStack.offerLast(previousSpell);
-      LOGGER.info("{} undoes {}", this, previousSpell);
+      previousSpell.run();
-      previousSpell.undo();
     }
   }
 
@@ -67,8 +65,7 @@ public class Wizard {
     if (!redoStack.isEmpty()) {
       var previousSpell = redoStack.pollLast();
       undoStack.offerLast(previousSpell);
-      LOGGER.info("{} redoes {}", this, previousSpell);
+      previousSpell.run();
-      previousSpell.redo();
     }
   }
 
@@ -79,84 +76,7 @@ public class Wizard {
 }
 ```
 
-Next we present the spell hierarchy.
+Next, we have the goblin who's the target of the spells.
-
-```java
-public interface Command {
-
-  void execute(Target target);
-
-  void undo();
-
-  void redo();
-
-  String toString();
-}
-
-public class InvisibilitySpell implements Command {
-
-  private Target target;
-
-  @Override
-  public void execute(Target target) {
-    target.setVisibility(Visibility.INVISIBLE);
-    this.target = target;
-  }
-
-  @Override
-  public void undo() {
-    if (target != null) {
-      target.setVisibility(Visibility.VISIBLE);
-    }
-  }
-
-  @Override
-  public void redo() {
-    if (target != null) {
-      target.setVisibility(Visibility.INVISIBLE);
-    }
-  }
-
-  @Override
-  public String toString() {
-    return "Invisibility spell";
-  }
-}
-
-public class ShrinkSpell implements Command {
-
-  private Size oldSize;
-  private Target target;
-
-  @Override
-  public void execute(Target target) {
-    oldSize = target.getSize();
-    target.setSize(Size.SMALL);
-    this.target = target;
-  }
-
-  @Override
-  public void undo() {
-    if (oldSize != null && target != null) {
-      var temp = target.getSize();
-      target.setSize(oldSize);
-      oldSize = temp;
-    }
-  }
-
-  @Override
-  public void redo() {
-    undo();
-  }
-
-  @Override
-  public String toString() {
-    return "Shrink spell";
-  }
-}
-```
-
-Finally, we have the goblin who's the target of the spells.
 
 ```java
 public abstract class Target {
@@ -203,33 +123,73 @@ public class Goblin extends Target {
     return "Goblin";
   }
 
+  public void changeSize() {
+    var oldSize = getSize() == Size.NORMAL ? Size.SMALL : Size.NORMAL;
+    setSize(oldSize);
+  }
+
+  public void changeVisibility() {
+    var visible = getVisibility() == Visibility.INVISIBLE
+          ? Visibility.VISIBLE : Visibility.INVISIBLE;
+    setVisibility(visible);
+  }
 }
 ```
 
+Finally we have the wizard in main function who casts spell
+
+```java
+public static void main(String[] args) {
+  var wizard = new Wizard();
+  var goblin = new Goblin();
+
+  // casts shrink/unshrink spell
+  wizard.castSpell(goblin::changeSize);
+
+  // casts visible/invisible spell
+  wizard.castSpell(goblin::changeVisibility);
+
+  // undo and redo casts
+   wizard.undoLastSpell();
+   wizard.redoLastSpell();
+```
+
 Here's the whole example in action.
 
 ```java
 var wizard = new Wizard();
 var goblin = new Goblin();
+
 goblin.printStatus();
-wizard.castSpell(new ShrinkSpell(), goblin);
+wizard.castSpell(goblin::changeSize);
 goblin.printStatus();
-wizard.castSpell(new InvisibilitySpell(), goblin);
+
+wizard.castSpell(goblin::changeVisibility);
 goblin.printStatus();
+
 wizard.undoLastSpell();
 goblin.printStatus();
+
+wizard.undoLastSpell();
+goblin.printStatus();
+
+wizard.redoLastSpell();
+goblin.printStatus();
+
+wizard.redoLastSpell();
+goblin.printStatus();
 ```
 
 Here's the program output:
 
 ```java
-// Goblin, [size=normal] [visibility=visible]
+Goblin, [size=normal] [visibility=visible]
-// Wizard casts Shrink spell at Goblin
+Goblin, [size=small] [visibility=visible]
-// Goblin, [size=small] [visibility=visible]
+Goblin, [size=small] [visibility=invisible]
-// Wizard casts Invisibility spell at Goblin
+Goblin, [size=small] [visibility=visible]
-// Goblin, [size=small] [visibility=invisible]
+Goblin, [size=normal] [visibility=visible]
-// Wizard undoes Invisibility spell
+Goblin, [size=small] [visibility=visible]
-// Goblin, [size=small] [visibility=visible]
+Goblin, [size=small] [visibility=invisible]
 ```
 
 ## Class diagram

command/etc/command.ucls

@@ -1,15 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <class-diagram version="1.1.8" icons="true" automaticImage="PNG" always-add-relationships="false" generalizations="true"
   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="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"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </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="-1" width="-1" x="129" y="1223"/>
@@ -28,24 +19,6 @@
       <operations public="true" package="true" protected="true" private="true" static="true"/>
     </display>
   </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="-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"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </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="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>  
   <class id="6" 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="-1" width="-1" x="129" y="1014"/>

command/etc/command.urm.puml

@@ -4,33 +4,11 @@ package com.iluwatar.command {
     + App()
     + main(args : String[]) {static}
   }
-  interface Command {
-    + Command()
-    + execute(Target) {abstract}
-    + redo() {abstract}
-    + toString() : String {abstract}
-    + undo() {abstract}
-  }
   class Goblin {
     + Goblin()
     + toString() : String
-  }
+    + changeSize()
-  class InvisibilitySpell {
+    + changeVisibility()
-    - target : Target
-    + InvisibilitySpell()
-    + execute(target : Target)
-    + redo()
-    + toString() : String
-    + undo()
-  }
-  class ShrinkSpell {
-    - oldSize : Size
-    - target : Target
-    + ShrinkSpell()
-    + execute(target : Target)
-    + redo()
-    + toString() : String
-    + undo()
   }
   enum Size {
     + NORMAL {static}
@@ -62,22 +40,19 @@ package com.iluwatar.command {
   }
   class Wizard {
     - LOGGER : Logger {static}
-    - redoStack : Deque<Command>
+    - redoStack : Deque<Runnable>
-    - undoStack : Deque<Command>
+    - undoStack : Deque<Runnable>
     + Wizard()
-    + castSpell(command : Command, target : Target)
+    + castSpell(Runnable : runnable)
     + redoLastSpell()
     + toString() : String
     + undoLastSpell()
   }
 }
 Target -->  "-size" Size
-Wizard -->  "-undoStack" Command
+Wizard -->  "-changeSize" Goblin
-ShrinkSpell -->  "-oldSize" Size
+Wizard -->  "-changeVisibility" Goblin
-InvisibilitySpell -->  "-target" Target
-ShrinkSpell -->  "-target" Target
 Target -->  "-visibility" Visibility
 Goblin --|> Target
-InvisibilitySpell ..|> Command
+App --> "castSpell" Wizard
-ShrinkSpell ..|> Command
 @enduml

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

@@ -30,12 +30,10 @@ package com.iluwatar.command;
  *
  * <p>Four terms always associated with the command pattern are command, receiver, invoker and
  * client. A command object (spell) knows about the receiver (target) and invokes a method of the
- * receiver. Values for parameters of the receiver method are stored in the command. The receiver
+ * receiver. An invoker object (wizard) receives a reference to the command to be executed and
- * then does the work. An invoker object (wizard) knows how to execute a command, and optionally
+ * optionally does bookkeeping about the command execution. The invoker does not know anything
- * does bookkeeping about the command execution. The invoker does not know anything about a concrete
+ * about how the command is executed. The client decides which commands to execute at which
- * command, it knows only about command interface. Both an invoker object and several command
+ * points. To execute a command, it passes a reference of the function to the invoker object.
- * 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.
  *
  * <p>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
@@ -54,10 +52,10 @@ public class App {
 
     goblin.printStatus();
 
-    wizard.castSpell(new ShrinkSpell(), goblin);
+    wizard.castSpell(goblin::changeSize);
     goblin.printStatus();
 
-    wizard.castSpell(new InvisibilitySpell(), goblin);
+    wizard.castSpell(goblin::changeVisibility);
     goblin.printStatus();
 
     wizard.undoLastSpell();

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

@@ -1,37 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-package com.iluwatar.command;
-
-/**
- * Interface for Commands.
- */
-public interface Command {
-  void execute(Target target);
-
-  void undo();
-
-  void redo();
-
-  String toString();
-}

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

@@ -23,11 +23,16 @@
 
 package com.iluwatar.command;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 /**
  * Goblin is the target of the spells.
  */
 public class Goblin extends Target {
 
+  private static final Logger LOGGER = LoggerFactory.getLogger(Goblin.class);
+
   public Goblin() {
     setSize(Size.NORMAL);
     setVisibility(Visibility.VISIBLE);
@@ -37,5 +42,4 @@ public class Goblin extends Target {
   public String toString() {
     return "Goblin";
   }
-
 }

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

@@ -1,57 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-package com.iluwatar.command;
-
-/**
- * InvisibilitySpell is a concrete command.
- */
-public class InvisibilitySpell implements Command {
-
-  private Target target;
-
-  @Override
-  public void execute(Target target) {
-    target.setVisibility(Visibility.INVISIBLE);
-    this.target = target;
-  }
-
-  @Override
-  public void undo() {
-    if (target != null) {
-      target.setVisibility(Visibility.VISIBLE);
-    }
-  }
-
-  @Override
-  public void redo() {
-    if (target != null) {
-      target.setVisibility(Visibility.INVISIBLE);
-    }
-  }
-
-  @Override
-  public String toString() {
-    return "Invisibility spell";
-  }
-}

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

@@ -1,59 +0,0 @@
-/*
- * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
- * THE SOFTWARE.
- */
-
-package com.iluwatar.command;
-
-/**
- * ShrinkSpell is a concrete command.
- */
-public class ShrinkSpell implements Command {
-
-  private Size oldSize;
-  private Target target;
-
-  @Override
-  public void execute(Target target) {
-    oldSize = target.getSize();
-    target.setSize(Size.SMALL);
-    this.target = target;
-  }
-
-  @Override
-  public void undo() {
-    if (oldSize != null && target != null) {
-      var temp = target.getSize();
-      target.setSize(oldSize);
-      oldSize = temp;
-    }
-  }
-
-  @Override
-  public void redo() {
-    undo();
-  }
-
-  @Override
-  public String toString() {
-    return "Shrink spell";
-  }
-}

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

@@ -62,4 +62,21 @@ public abstract class Target {
   public void printStatus() {
     LOGGER.info("{}, [size={}] [visibility={}]", this, getSize(), getVisibility());
   }
+
+  /**
+   * Changes the size of the target.
+   */
+  public void changeSize() {
+    var oldSize = getSize() == Size.NORMAL ? Size.SMALL : Size.NORMAL;
+    setSize(oldSize);
+  }
+
+  /**
+   * Changes the visibility of the target.
+   */
+  public void changeVisibility() {
+    var visible = getVisibility() == Visibility.INVISIBLE
+            ? Visibility.VISIBLE : Visibility.INVISIBLE;
+    setVisibility(visible);
+  }
 }

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

@@ -35,20 +35,18 @@ public class Wizard {
 
   private static final Logger LOGGER = LoggerFactory.getLogger(Wizard.class);
 
-  private final Deque<Command> undoStack = new LinkedList<>();
+  private final Deque<Runnable> undoStack = new LinkedList<>();
-  private final Deque<Command> redoStack = new LinkedList<>();
+  private final Deque<Runnable> redoStack = new LinkedList<>();
 
   public Wizard() {
-    // comment to ignore sonar issue: LEVEL critical
   }
 
   /**
    * Cast spell.
    */
-  public void castSpell(Command command, Target target) {
+  public void castSpell(Runnable runnable) {
-    LOGGER.info("{} casts {} at {}", this, command, target);
+    runnable.run();
-    command.execute(target);
+    undoStack.offerLast(runnable);
-    undoStack.offerLast(command);
   }
 
   /**
@@ -58,8 +56,7 @@ public class Wizard {
     if (!undoStack.isEmpty()) {
       var previousSpell = undoStack.pollLast();
       redoStack.offerLast(previousSpell);
-      LOGGER.info("{} undoes {}", this, previousSpell);
+      previousSpell.run();
-      previousSpell.undo();
     }
   }
 
@@ -70,8 +67,7 @@ public class Wizard {
     if (!redoStack.isEmpty()) {
       var previousSpell = redoStack.pollLast();
       undoStack.offerLast(previousSpell);
-      LOGGER.info("{} redoes {}", this, previousSpell);
+      previousSpell.run();
-      previousSpell.redo();
     }
   }
 

command/src/test/java/com/iluwatar/command/CommandTest.java

@@ -56,10 +56,10 @@ public class CommandTest {
     var wizard = new Wizard();
     var goblin = new Goblin();
 
-    wizard.castSpell(new ShrinkSpell(), goblin);
+    wizard.castSpell(goblin::changeSize);
     verifyGoblin(goblin, GOBLIN, Size.SMALL, Visibility.VISIBLE);
 
-    wizard.castSpell(new InvisibilitySpell(), goblin);
+    wizard.castSpell(goblin::changeVisibility);
     verifyGoblin(goblin, GOBLIN, Size.SMALL, Visibility.INVISIBLE);
 
     wizard.undoLastSpell();