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Copy file name to clipboardExpand all lines: twin/README.md
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Twin pattern is a design pattern which provides a standard solution to simulate multiple
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inheritance in java
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##Explanation
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Real-world example
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>Consider a game with a ball that needs features of two types, Game Item, and threads to function
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>smoothly in the game. We can use two objects, with one object compatible with the first type and
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>the other compatible with the second type.
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>The pair of objects together can function as one ball in the game.
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In plain words
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>It provides a way to form two closely coupled sub-classes that can act as a twin class having two ends.
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Wikipedia says
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>In software engineering, the Twin pattern is a software design pattern that allows developers
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>to model multiple inheritance in programming languages that do not support multiple inheritance.
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>This pattern avoids many of the problems with multiple inheritance.
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**Programmatic Example**
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Take our game ball example from above. Consider we have a game in which the ball needs to be both a`GameItem` and`Thread`.
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First of all, we have the`GameItem` class given below and the`Thread` class.
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```java
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@Slf4j
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publicabstractclassGameItem {
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publicvoiddraw() {
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LOGGER.info("draw");
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doDraw();
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}
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publicabstractvoiddoDraw();
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publicabstractvoidclick();
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}
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```
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Then, we have subclasses`BallItem` and`BallThread` inheriting them, respectively.
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```java
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@Slf4j
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publicclassBallItemextendsGameItem {
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privateboolean isSuspended;
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@Setter
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privateBallThread twin;
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@Override
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publicvoiddoDraw() {
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LOGGER.info("doDraw");
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}
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publicvoidmove() {
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LOGGER.info("move");
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}
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@Override
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publicvoidclick() {
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isSuspended=!isSuspended;
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if (isSuspended) {
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twin.suspendMe();
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}else {
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twin.resumeMe();
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}
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}
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}
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@Slf4j
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publicclassBallThreadextendsThread {
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@Setter
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privateBallItem twin;
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privatevolatileboolean isSuspended;
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privatevolatileboolean isRunning=true;
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/**
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* Run the thread.
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*/
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publicvoidrun() {
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while (isRunning) {
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if (!isSuspended) {
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twin.draw();
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twin.move();
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}
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try {
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Thread.sleep(250);
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}catch (InterruptedException e) {
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thrownewRuntimeException(e);
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}
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}
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}
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publicvoidsuspendMe() {
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isSuspended=true;
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LOGGER.info("Begin to suspend BallThread");
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}
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publicvoidresumeMe() {
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isSuspended=false;
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LOGGER.info("Begin to resume BallThread");
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}
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publicvoidstopMe() {
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this.isRunning=false;
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this.isSuspended=true;
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}
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}
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```
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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.