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Author SHA1 Message Date
Subhrodip Mohanta
c95a2a1413 Removed Conflicts 2021-10-21 23:35:03 +05:30
allcontributors[bot]
657c16720e docs: update .all-contributorsrc [skip ci] 2021-10-21 23:35:03 +05:30
allcontributors[bot]
d77915a3b7 docs: update README.md [skip ci] 2021-10-21 23:34:22 +05:30
4 changed files with 1 additions and 165 deletions

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@@ -1676,24 +1676,6 @@
"contributions": [
"translation"
]
},
{
"login": "ManviGoel26",
"name": "Manvi Goel",
"avatar_url": "https://avatars.githubusercontent.com/u/55682355?v=4",
"profile": "https://github.com/ManviGoel26",
"contributions": [
"doc"
]
},
{
"login": "blueberry404",
"name": "Anum Amin",
"avatar_url": "https://avatars.githubusercontent.com/u/39243539?v=4",
"profile": "https://github.com/blueberry404",
"contributions": [
"doc"
]
}
],
"contributorsPerLine": 7,

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@@ -10,7 +10,7 @@
[![Coverage](https://sonarcloud.io/api/project_badges/measure?project=iluwatar_java-design-patterns&metric=coverage)](https://sonarcloud.io/dashboard?id=iluwatar_java-design-patterns)
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<!-- ALL-CONTRIBUTORS-BADGE:START - Do not remove or modify this section -->
[![All Contributors](https://img.shields.io/badge/all_contributors-186-orange.svg?style=flat-square)](#contributors-)
[![All Contributors](https://img.shields.io/badge/all_contributors-183-orange.svg?style=flat-square)](#contributors-)
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<br/>
@@ -312,8 +312,6 @@ This project is licensed under the terms of the MIT license.
<tr>
<td align="center"><a href="http://carlfx.wordpress.com"><img src="https://avatars.githubusercontent.com/u/1594624?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Carl Dea</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=carldea" title="Code">💻</a></td>
<td align="center"><a href="https://github.com/Mozartuss"><img src="https://avatars.githubusercontent.com/u/32893711?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Mozartus</b></sub></a><br /><a href="#translation-Mozartuss" title="Translation">🌍</a></td>
<td align="center"><a href="https://github.com/ManviGoel26"><img src="https://avatars.githubusercontent.com/u/55682355?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Manvi Goel</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=ManviGoel26" title="Documentation">📖</a></td>
<td align="center"><a href="https://github.com/blueberry404"><img src="https://avatars.githubusercontent.com/u/39243539?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Anum Amin</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=blueberry404" title="Documentation">📖</a></td>
</tr>
</table>

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@@ -13,144 +13,6 @@ tags:
Twin pattern is a design pattern which provides a standard solution to simulate multiple
inheritance in java
## Explanation
Real-world example
> Consider a game with a ball that needs features of two types, Game Item, and threads to function
> smoothly in the game. We can use two objects, with one object compatible with the first type and
> the other compatible with the second type.
> The pair of objects together can function as one ball in the game.
In plain words
> It provides a way to form two closely coupled sub-classes that can act as a twin class having two ends.
Wikipedia says
> In software engineering, the Twin pattern is a software design pattern that allows developers
> to model multiple inheritance in programming languages that do not support multiple inheritance.
> This pattern avoids many of the problems with multiple inheritance.
**Programmatic Example**
Take our game ball example from above. Consider we have a game in which the ball needs to be both a `GameItem` and `Thread`.
First of all, we have the `GameItem` class given below and the `Thread` class.
```java
@Slf4j
public abstract class GameItem {
public void draw() {
LOGGER.info("draw");
doDraw();
}
public abstract void doDraw();
public abstract void click();
}
```
Then, we have subclasses `BallItem` and `BallThread` inheriting them, respectively.
```java
@Slf4j
public class BallItem extends GameItem {
private boolean isSuspended;
@Setter
private BallThread twin;
@Override
public void doDraw() {
LOGGER.info("doDraw");
}
public void move() {
LOGGER.info("move");
}
@Override
public void click() {
isSuspended = !isSuspended;
if (isSuspended) {
twin.suspendMe();
} else {
twin.resumeMe();
}
}
}
@Slf4j
public class BallThread extends Thread {
@Setter
private BallItem twin;
private volatile boolean isSuspended;
private volatile boolean isRunning = true;
/**
* Run the thread.
*/
public void run() {
while (isRunning) {
if (!isSuspended) {
twin.draw();
twin.move();
}
try {
Thread.sleep(250);
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
}
}
public void suspendMe() {
isSuspended = true;
LOGGER.info("Begin to suspend BallThread");
}
public void resumeMe() {
isSuspended = false;
LOGGER.info("Begin to resume BallThread");
}
public void stopMe() {
this.isRunning = false;
this.isSuspended = true;
}
}
```
Now, when we need the ball, we can instantiate objects from both the `BallThread` and `BallItem` as a pair and pass them to its pair object so they can act together as appropriate.
```java
var ballItem = new BallItem();
var ballThread = new BallThread();
ballItem.setTwin(ballThread);
ballThread.setTwin(ballItem);
```
## Class diagram
![alt text](./etc/twin.png "Twin")

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@@ -214,12 +214,6 @@ Use the Visitor pattern when
* Many distinct and unrelated operations need to be performed on objects in an object structure, and you want to avoid "polluting" their classes with these operations. Visitor lets you keep related operations together by defining them in one class. When the object structure is shared by many applications, use Visitor to put operations in just those applications that need them.
* The classes defining the object structure rarely change, but you often want to define new operations over the structure. Changing the object structure classes requires redefining the interface to all visitors, which is potentially costly. If the object structure classes change often, then it's probably better to define the operations in those classes.
## Tutorials
* [Refactoring Guru](https://refactoring.guru/design-patterns/visitor)
* [Dzone](https://dzone.com/articles/design-patterns-visitor)
* [Sourcemaking](https://sourcemaking.com/design_patterns/visitor)
## Known uses
* [Apache Wicket](https://github.com/apache/wicket) component tree, see [MarkupContainer](https://github.com/apache/wicket/blob/b60ec64d0b50a611a9549809c9ab216f0ffa3ae3/wicket-core/src/main/java/org/apache/wicket/MarkupContainer.java)