gaspersic/java-design-patterns
1
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

Merge pull request #1531 from ravening/command-functional

Browse Source 
Refactor the command pattern to use lambda functions
This commit is contained in:
Ilkka Seppälä
2020-11-08 19:33:48 +02:00
committed by GitHub
parent 5a8933ea17 af1b611136
commit 7c0fdad5a2
12 changed files with 208 additions and 438 deletions
Download Patch File Download Diff File Expand all files Collapse all files

150
command/README.md
View File

@@ -48,18 +48,16 @@ public class Wizard {
public Wizard() {}
public void castSpell(Command command, Target target) {
LOGGER.info("{} casts {} at {}", this, command, target);
command.execute(target);
undoStack.offerLast(command);
public void castSpell(Runnable runnable) {
runnable.run();
undoStack.offerLast(runnable);
}
public void undoLastSpell() {
if (!undoStack.isEmpty()) {
var previousSpell = undoStack.pollLast();
redoStack.offerLast(previousSpell);
LOGGER.info("{} undoes {}", this, previousSpell);
previousSpell.undo();
previousSpell.run();
}
}
@@ -67,8 +65,7 @@ public class Wizard {
if (!redoStack.isEmpty()) {
var previousSpell = redoStack.pollLast();
undoStack.offerLast(previousSpell);
LOGGER.info("{} redoes {}", this, previousSpell);
previousSpell.redo();
previousSpell.run();
}
}
@@ -79,84 +76,7 @@ public class Wizard {
}
```
Next we present the spell hierarchy.
```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.
Next, 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]
// Wizard casts Shrink spell at Goblin
// Goblin, [size=small] [visibility=visible]
// Wizard casts Invisibility spell at Goblin
// Goblin, [size=small] [visibility=invisible]
// Wizard undoes Invisibility spell
// Goblin, [size=small] [visibility=visible]
Goblin, [size=normal] [visibility=visible]
Goblin, [size=small] [visibility=visible]
Goblin, [size=small] [visibility=invisible]
Goblin, [size=small] [visibility=visible]
Goblin, [size=normal] [visibility=visible]
Goblin, [size=small] [visibility=visible]
Goblin, [size=small] [visibility=invisible]
```
## Class diagram

BIN
command/etc/command.png
View File

Binary file not shown.
Side by Side Swipe Overlay

Before

Width:  |  Height:  |  Size: 75 KiB

After

Width:  |  Height:  |  Size: 50 KiB

27
command/etc/command.ucls
View File

@@ -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"/>

41
command/etc/command.urm.puml
View File

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

14
command/src/main/java/com/iluwatar/command/App.java
View File

@@ -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
* 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.
* receiver. An invoker object (wizard) receives a reference to the command to be executed and
* optionally does bookkeeping about the command execution. The invoker does not know anything
* about how the command is executed. The client decides which commands to execute at which
* points. To execute a command, it passes a reference of the function 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();

37
command/src/main/java/com/iluwatar/command/Command.java
View File

@@ -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();
}

6
command/src/main/java/com/iluwatar/command/Goblin.java
View File

@@ -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";
}
}

57
command/src/main/java/com/iluwatar/command/InvisibilitySpell.java
View File

@@ -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";
}
}

59
command/src/main/java/com/iluwatar/command/ShrinkSpell.java
View File

@@ -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";
}
}

17
command/src/main/java/com/iluwatar/command/Target.java
View File

@@ -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);
}
}

18
command/src/main/java/com/iluwatar/command/Wizard.java
View File

@@ -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<Command> redoStack = new LinkedList<>();
private final Deque<Runnable> undoStack = 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) {
LOGGER.info("{} casts {} at {}", this, command, target);
command.execute(target);
undoStack.offerLast(command);
public void castSpell(Runnable runnable) {
runnable.run();
undoStack.offerLast(runnable);
}
/**
@@ -58,8 +56,7 @@ public class Wizard {
if (!undoStack.isEmpty()) {
var previousSpell = undoStack.pollLast();
redoStack.offerLast(previousSpell);
LOGGER.info("{} undoes {}", this, previousSpell);
previousSpell.undo();
previousSpell.run();
}
}
@@ -70,8 +67,7 @@ public class Wizard {
if (!redoStack.isEmpty()) {
var previousSpell = redoStack.pollLast();
undoStack.offerLast(previousSpell);
LOGGER.info("{} redoes {}", this, previousSpell);
previousSpell.redo();
previousSpell.run();
}
}

4
command/src/test/java/com/iluwatar/command/CommandTest.java
View File

@@ -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();