task: Explanations and grammar fixes for all the GoF patterns (#1791)

* Grammatical fixes to command pattern

* Update bridge pattern readme

* Fixes to builder pattern grammar

* Update chain of responsibility

* Improvements to the composite example

* Fixes to headings

* Minor updates to decorator pattern

* Update facade

* Update factory example

* Update factory method

* Update flyweight

* Interpreter explanation

* Update iterator readme

* Add explanation for mediator pattern

* Grammatical fixes to memento

* Grammar fixes for observer

* Update explanation for the prototype pattern

* Proxy pattern grammar fixes

* Update singleton

* Grammar fixes to state pattern

* Grammar fixes for strategy

* Grammar fixes, template method

* Grammar fixes for visitor

* Fix typo

abstract-factory/README.md

@@ -196,13 +196,13 @@ Example use cases
 * Unit test case writing becomes much easier
 * UI tools for different OS
 
-## Consequences:
+## Consequences
 
 * Dependency injection in java hides the service class dependencies that can lead to runtime errors that would have been caught at compile time.
 * While the pattern is great when creating predefined objects, adding the new ones might be challenging.
 * The code becomes more complicated than it should be since a lot of new interfaces and classes are introduced along with the pattern.
 
-## Tutorial
+## Tutorials
 
 * [Abstract Factory Pattern Tutorial](https://www.journaldev.com/1418/abstract-factory-design-pattern-in-java) 
 

adapter/README.md

@@ -105,7 +105,7 @@ Use the Adapter pattern when
 * you need to use several existing subclasses, but it's impractical to adapt their interface by subclassing every one. An object adapter can adapt the interface of its parent class.
 * most of the applications using third party libraries use adapters as a middle layer between the application and the 3rd party library to decouple the application from the library. If another library has to be used only an adapter for the new library is required without having to change the application code.
 
-## Consequences:
+## Consequences
 Class and object adapters have different trade-offs. A class adapter
 
 *	adapts Adaptee to Target by committing to a concrete Adaptee class. As a consequence, a class adapter won’t work when we want to adapt a class and all its subclasses.
@@ -118,7 +118,7 @@ An object adapter
 *	makes it harder to override Adaptee behavior. It will require subclassing Adaptee and making Adapter refer to the subclass rather than the Adaptee itself.
 
 
-## Real world examples
+## Known uses
 
 * [java.util.Arrays#asList()](http://docs.oracle.com/javase/8/docs/api/java/util/Arrays.html#asList%28T...%29)
 * [java.util.Collections#list()](https://docs.oracle.com/javase/8/docs/api/java/util/Collections.html#list-java.util.Enumeration-)

bridge/README.md

@@ -19,7 +19,7 @@ Decouple an abstraction from its implementation so that the two can vary indepen
 
 ## Explanation
 
-Real world example
+Real-world example
 
 > Consider you have a weapon with different enchantments, and you are supposed to allow mixing 
 > different weapons with different enchantments. What would you do? Create multiple copies of each 
@@ -161,27 +161,36 @@ public class SoulEatingEnchantment implements Enchantment {
 Here are both hierarchies in action:
 
 ```java
+LOGGER.info("The knight receives an enchanted sword.");
 var enchantedSword = new Sword(new SoulEatingEnchantment());
 enchantedSword.wield();
 enchantedSword.swing();
 enchantedSword.unwield();
-// The sword is wielded.
-// The item spreads bloodlust.
-// The sword is swinged.
-// The item eats the soul of enemies.
-// The sword is unwielded.
-// Bloodlust slowly disappears.
 
+LOGGER.info("The valkyrie receives an enchanted hammer.");
 var hammer = new Hammer(new FlyingEnchantment());
 hammer.wield();
 hammer.swing();
 hammer.unwield();
-// The hammer is wielded.
-// The item begins to glow faintly.
-// The hammer is swinged.
-// The item flies and strikes the enemies finally returning to owner's hand.
-// The hammer is unwielded.
-// The item's glow fades.
+```
+
+Here's the console output.
+
+```
+The knight receives an enchanted sword.
+The sword is wielded.
+The item spreads bloodlust.
+The sword is swung.
+The item eats the soul of enemies.
+The sword is unwielded.
+Bloodlust slowly disappears.
+The valkyrie receives an enchanted hammer.
+The hammer is wielded.
+The item begins to glow faintly.
+The hammer is swung.
+The item flies and strikes the enemies finally returning to owner's hand.
+The hammer is unwielded.
+The item's glow fades.
 ```
 
 ## Class diagram

builder/README.md

@@ -16,11 +16,11 @@ process can create different representations.
 
 ## Explanation
 
-Real world example
+Real-world example
 
 > Imagine a character generator for a role-playing game. The easiest option is to let the computer 
 > create the character for you. If you want to manually select the character details like 
-> profession, gender, hair color etc. the character generation becomes a step-by-step process that 
+> profession, gender, hair color, etc. the character generation becomes a step-by-step process that 
 > completes when all the selections are ready.
 
 In plain words
@@ -49,7 +49,7 @@ anti-pattern.
 
 **Programmatic Example**
 
-The sane alternative is to use the Builder pattern. First of all we have our hero that we want to 
+The sane alternative is to use the Builder pattern. First of all, we have our hero that we want to 
 create:
 
 ```java
@@ -134,7 +134,7 @@ Use the Builder pattern when
 * The algorithm for creating a complex object should be independent of the parts that make up the object and how they're assembled
 * The construction process must allow different representations for the object that's constructed
 
-## Real world examples
+## Known uses
 
 * [java.lang.StringBuilder](http://docs.oracle.com/javase/8/docs/api/java/lang/StringBuilder.html)
 * [java.nio.ByteBuffer](http://docs.oracle.com/javase/8/docs/api/java/nio/ByteBuffer.html#put-byte-) as well as similar buffers such as FloatBuffer, IntBuffer and so on.

chain/README.md → chain-of-responsibility/README.md

@@ -1,25 +1,26 @@
 ---
 layout: pattern
 title: Chain of responsibility
-folder: chain
-permalink: /patterns/chain/
+folder: chain-of-responsibility
+permalink: /patterns/chain-of-responsibility/
 categories: Behavioral
 language: en
 tags:
  - Gang of Four
 ---
 
 ## Intent
+
 Avoid coupling the sender of a request to its receiver by giving more than one object a chance to 
 handle the request. Chain the receiving objects and pass the request along the chain until an object 
 handles it.
 
 ## Explanation
 
-Real world example
+Real-world example
 
 > The Orc King gives loud orders to his army. The closest one to react is the commander, then 
-> officer and then soldier. The commander, officer and soldier here form a chain of responsibility.
+> an officer, and then a soldier. The commander, officer, and soldier form a chain of responsibility.
 
 In plain words
 
@@ -35,7 +36,7 @@ Wikipedia says
 
 **Programmatic Example**
 
-Translating our example with the orcs from above. First we have the `Request` class:
+Translating our example with the orcs from above. First, we have the `Request` class:
 
 ```java
 public class Request {
@@ -66,7 +67,7 @@ public enum RequestType {
 }
 ```
 
-Then the request handler hierarchy
+Next, we show the request handler hierarchy.
 
 ```java
 @Slf4j
@@ -116,7 +117,7 @@ public class OrcCommander extends RequestHandler {
 
 ```
 
-Then we have the Orc King who gives the orders and forms the chain
+The Orc King gives the orders and forms the chain.
 
 ```java
 public class OrcKing {
@@ -136,18 +137,26 @@ public class OrcKing {
 }
 ```
 
-Then it is used as follows
+The chain of responsibility in action.
 
 ```java
 var king = new OrcKing();
-king.makeRequest(new Request(RequestType.DEFEND_CASTLE, "defend castle")); // Orc commander handling request "defend castle"
-king.makeRequest(new Request(RequestType.TORTURE_PRISONER, "torture prisoner")); // Orc officer handling request "torture prisoner"
-king.makeRequest(new Request(RequestType.COLLECT_TAX, "collect tax")); // Orc soldier handling request "collect tax"
+king.makeRequest(new Request(RequestType.DEFEND_CASTLE, "defend castle"));
+king.makeRequest(new Request(RequestType.TORTURE_PRISONER, "torture prisoner"));
+king.makeRequest(new Request(RequestType.COLLECT_TAX, "collect tax"));
+```
+
+The console output.
+
+```
+Orc commander handling request "defend castle"
+Orc officer handling request "torture prisoner"
+Orc soldier handling request "collect tax"
 ```
 
 ## Class diagram
 
-![alt text](./etc/chain.urm.png "Chain of Responsibility class diagram")
+![alt text](./etc/chain-of-responsibility.urm.png "Chain of Responsibility class diagram")
 
 ## Applicability
 
@@ -157,7 +166,7 @@ Use Chain of Responsibility when
 * You want to issue a request to one of several objects without specifying the receiver explicitly.
 * The set of objects that can handle a request should be specified dynamically.
 
-## Real world examples
+## Known uses
 
 * [java.util.logging.Logger#log()](http://docs.oracle.com/javase/8/docs/api/java/util/logging/Logger.html#log%28java.util.logging.Level,%20java.lang.String%29)
 * [Apache Commons Chain](https://commons.apache.org/proper/commons-chain/index.html)

chain/pom.xml → chain-of-responsibility/pom.xml

@@ -31,7 +31,7 @@
     <artifactId>java-design-patterns</artifactId>
     <version>1.25.0-SNAPSHOT</version>
   </parent>
-  <artifactId>chain</artifactId>
+  <artifactId>chain-of-responsibility</artifactId>
   <dependencies>
     <dependency>
       <groupId>org.junit.jupiter</groupId>

command/README.md

@@ -1,4 +1,4 @@
----
+ ---
 layout: pattern
 title: Command
 folder: command
@@ -19,7 +19,7 @@ Encapsulate a request as an object, thereby letting you parameterize clients wit
 requests, queue or log requests, and support undoable operations.
 
 ## Explanation
-Real world example
+Real-world example
 
 > There is a wizard casting spells on a goblin. The spells are executed on the goblin one by one.
 > The first spell shrinks the goblin and the second makes him invisible. Then the wizard reverses
@@ -135,7 +135,7 @@ public class Goblin extends Target {
 }
 ```
 
-Finally we have the wizard in main function who casts spell
+Finally, we have the wizard in the main function casting spells.
 
 ```java
 public static void main(String[] args) {
@@ -202,32 +202,29 @@ Use the Command pattern when you want to:
 * Parameterize objects by an action to perform. You can express such parameterization in a
 procedural language with a callback function, that is, a function that's registered somewhere to be
 called at a later point. Commands are an object-oriented replacement for callbacks.
-* Specify, queue, and execute requests at different times. A Command object can have a lifetime
+* Specify, queue, and execute requests at different times. A Command object can have a life
 independent of the original request. If the receiver of a request can be represented in an address
 space-independent way, then you can transfer a command object for the request to a different process
 and fulfill the request there.
 * Support undo. The Command's execute operation can store state for reversing its effects in the
 command itself. The Command interface must have an added un-execute operation that reverses the
 effects of a previous call to execute. The executed commands are stored in a history list.
-Unlimited-level undo and redo is achieved by traversing this list backwards and forwards calling
-un-execute and execute, respectively.
+Unlimited-level undo and redo functionality is achieved by traversing this list backward and forward 
+  calling un-execute and execute, respectively.
 * Support logging changes so that they can be reapplied in case of a system crash. By augmenting the
 Command interface with load and store operations, you can keep a persistent log of changes.
-Recovering from a crash involves reloading logged commands from disk and re-executing them with
+Recovering from a crash involves reloading logged commands from the disk and re-executing them with
 the execute operation.
 * Structure a system around high-level operations build on primitive operations. Such a structure is
-common in information systems that support transactions. A transaction encapsulates a set of changes
-to data. The Command pattern offers a way to model transactions. Commands have a common interface,
+common in information systems that support transactions. A transaction encapsulates a set of data
+changes. The Command pattern offers a way to model transactions. Commands have a common interface,
 letting you invoke all transactions the same way. The pattern also makes it easy to extend the
 system with new transactions.
+* Keep a history of requests.
+* Implement callback functionality.
+* Implement the undo functionality.
 
-## Typical Use Case
-
-* To keep a history of requests
-* Implement callback functionality
-* Implement the undo functionality
-
-## Real world examples
+## Known uses
 
 * [java.lang.Runnable](http://docs.oracle.com/javase/8/docs/api/java/lang/Runnable.html)
 * [org.junit.runners.model.Statement](https://github.com/junit-team/junit4/blob/master/src/main/java/org/junit/runners/model/Statement.java)

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

@@ -26,7 +26,7 @@
 /**
  * The Command pattern is a behavioral design pattern in which an object is used to encapsulate all
  * information needed to perform an action or trigger an event at a later time. This information
- * includes the method name, the object that owns the method and values for the method parameters.
+ * includes the method name, the object that owns the method, and values for the method parameters.
  *
  * <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

composite/README.md

@@ -16,15 +16,15 @@ treat individual objects and compositions of objects uniformly.
 
 ## Explanation
 
-Real world example
+Real-world example
 
 > Every sentence is composed of words which are in turn composed of characters. Each of these 
-> objects is printable and they can have something printed before or after them like sentence always 
-> ends with full stop and word always has space before it.
+> objects are printable and they can have something printed before or after them like sentence 
+> always ends with full stop and word always has space before it.
 
 In plain words
 
-> Composite pattern lets clients treat the individual objects in a uniform manner.
+> Composite pattern lets clients uniformly treat the individual objects.
 
 Wikipedia says
 
@@ -154,10 +154,22 @@ public class Messenger {
 And then it can be used as:
 
 ```java
-var orcMessage = new Messenger().messageFromOrcs();
-orcMessage.print(); // Where there is a whip there is a way.
-var elfMessage = new Messenger().messageFromElves();
-elfMessage.print(); // Much wind pours from your mouth.
+var messenger = new Messenger();
+
+LOGGER.info("Message from the orcs: ");
+messenger.messageFromOrcs().print();
+
+LOGGER.info("Message from the elves: ");
+messenger.messageFromElves().print();
+```
+
+The console output:
+
+```
+Message from the orcs: 
+ Where there is a whip there is a way.
+Message from the elves: 
+ Much wind pours from your mouth.
 ```
 
 ## Class diagram
@@ -172,7 +184,7 @@ Use the Composite pattern when
 * You want clients to be able to ignore the difference between compositions of objects and 
 individual objects. Clients will treat all objects in the composite structure uniformly.
 
-## Real world examples
+## Known uses
 
 * [java.awt.Container](http://docs.oracle.com/javase/8/docs/api/java/awt/Container.html) and [java.awt.Component](http://docs.oracle.com/javase/8/docs/api/java/awt/Component.html)
 * [Apache Wicket](https://github.com/apache/wicket) component tree, see [Component](https://github.com/apache/wicket/blob/91e154702ab1ff3481ef6cbb04c6044814b7e130/wicket-core/src/main/java/org/apache/wicket/Component.java) and [MarkupContainer](https://github.com/apache/wicket/blob/b60ec64d0b50a611a9549809c9ab216f0ffa3ae3/wicket-core/src/main/java/org/apache/wicket/MarkupContainer.java)

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

@@ -45,14 +45,13 @@ public class App {
    * @param args command line args
    */
   public static void main(String[] args) {
-    LOGGER.info("Message from the orcs: ");
 
-    var orcMessage = new Messenger().messageFromOrcs();
-    orcMessage.print();
+    var messenger = new Messenger();
 
-    LOGGER.info("\nMessage from the elves: ");
+    LOGGER.info("Message from the orcs: ");
+    messenger.messageFromOrcs().print();
 
-    var elfMessage = new Messenger().messageFromElves();
-    elfMessage.print();
+    LOGGER.info("Message from the elves: ");
+    messenger.messageFromElves().print();
   }
 }

composite/src/main/java/com/iluwatar/composite/Sentence.java

@@ -39,6 +39,6 @@ public Sentence(List<Word> words) {
 
   @Override
   protected void printThisAfter() {
-    System.out.print(".");
+    System.out.print(".\n");
   }
 }