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Ilkka Seppälä
2020-09-01 20:06:47 +03:00
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@ -10,16 +10,19 @@ tags:
---
## Intent
Specify the kinds of objects to create using a prototypical instance, and create new objects by copying this prototype.
Specify the kinds of objects to create using a prototypical instance, and create new objects by
copying this prototype.
## Explanation
First it should be noted that Prototype pattern is not used to gain performance benefits. It's only used for creating
new objects from prototype instance.
First it should be noted that Prototype pattern is not used to gain performance benefits. It's only
used for creating new objects from prototype instance.
Real world example
> Remember Dolly? The sheep that was cloned! Lets not get into the details but the key point here is that it is all about cloning.
> Remember Dolly? The sheep that was cloned! Lets not get into the details but the key point here is
> that it is all about cloning.
In plain words
@ -27,9 +30,12 @@ In plain words
Wikipedia says
> The prototype pattern is a creational design pattern in software development. It is used when the type of objects to create is determined by a prototypical instance, which is cloned to produce new objects.
> The prototype pattern is a creational design pattern in software development. It is used when the
> type of objects to create is determined by a prototypical instance, which is cloned to produce new
> objects.
In short, it allows you to create a copy of an existing object and modify it to your needs, instead of going through the trouble of creating an object from scratch and setting it up.
In short, it allows you to create a copy of an existing object and modify it to your needs, instead
of going through the trouble of creating an object from scratch and setting it up.
**Programmatic Example**
@ -52,7 +58,7 @@ class Sheep implements Cloneable {
}
```
Then it can be cloned like below
Then it can be cloned like below:
```java
var original = new Sheep("Jolly");
@ -65,15 +71,20 @@ System.out.println(cloned.getName()); // Dolly
```
## Class diagram
![alt text](./etc/prototype.urm.png "Prototype pattern class diagram")
## Applicability
Use the Prototype pattern when a system should be independent of how its products are created, composed and represented; and
* When the classes to instantiate are specified at run-time, for example, by dynamic loading
* To avoid building a class hierarchy of factories that parallels the class hierarchy of products
* When instances of a class can have one of only a few different combinations of state. It may be more convenient to install a corresponding number of prototypes and clone them rather than instantiating the class manually, each time with the appropriate state
* When object creation is expensive compared to cloning
Use the Prototype pattern when a system should be independent of how its products are created,
composed, represented and
* When the classes to instantiate are specified at run-time, for example, by dynamic loading.
* To avoid building a class hierarchy of factories that parallels the class hierarchy of products.
* When instances of a class can have one of only a few different combinations of state. It may be
more convenient to install a corresponding number of prototypes and clone them rather than
instantiating the class manually, each time with the appropriate state.
* When object creation is expensive compared to cloning.
## Real world examples