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prototype/README.md
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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

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proxy/README.md
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@ -10,16 +10,20 @@ tags:
---
## Also known as
Surrogate
## Intent
Provide a surrogate or placeholder for another object to control
access to it.
Provide a surrogate or placeholder for another object to control access to it.
## Explanation
Real world example
> Imagine a tower where the local wizards go to study their spells. The ivory tower can only be accessed through a proxy which ensures that only the first three wizards can enter. Here the proxy represents the functionality of the tower and adds access control to it.
> Imagine a tower where the local wizards go to study their spells. The ivory tower can only be
> accessed through a proxy which ensures that only the first three wizards can enter. Here the proxy
> represents the functionality of the tower and adds access control to it.
In plain words
@ -27,11 +31,17 @@ In plain words
Wikipedia says
> A proxy, in its most general form, is a class functioning as an interface to something else. A proxy is a wrapper or agent object that is being called by the client to access the real serving object behind the scenes. Use of the proxy can simply be forwarding to the real object, or can provide additional logic. In the proxy extra functionality can be provided, for example caching when operations on the real object are resource intensive, or checking preconditions before operations on the real object are invoked.
> A proxy, in its most general form, is a class functioning as an interface to something else.
> A proxy is a wrapper or agent object that is being called by the client to access the real serving
> object behind the scenes. Use of the proxy can simply be forwarding to the real object, or can
> provide additional logic. In the proxy extra functionality can be provided, for example caching
> when operations on the real object are resource intensive, or checking preconditions before
> operations on the real object are invoked.
**Programmatic Example**
Taking our wizard tower example from above. Firstly we have the wizard tower interface and the ivory tower class
Taking our wizard tower example from above. Firstly we have the `WizardTower` interface and the
`IvoryTower` class.
```java
public interface WizardTower {
@ -50,7 +60,7 @@ public class IvoryTower implements WizardTower {
}
```
Then a simple wizard class
Then a simple `Wizard` class.
```java
public class Wizard {
@ -68,7 +78,7 @@ public class Wizard {
}
```
Then we have the proxy to add access control to wizard tower
Then we have the `WizardTowerProxy` to add access control to `WizardTower`.
```java
public class WizardTowerProxy implements WizardTower {
@ -97,28 +107,41 @@ public class WizardTowerProxy implements WizardTower {
}
```
And here is tower entering scenario
And here is the tower entering scenario.
```java
var proxy = new WizardTowerProxy(new IvoryTower());
proxy.enter(new Wizard("Red wizard")); // Red wizard enters the tower.
proxy.enter(new Wizard("White wizard")); // White wizard enters the tower.
proxy.enter(new Wizard("Black wizard")); // Black wizard enters the tower.
proxy.enter(new Wizard("Green wizard")); // Green wizard is not allowed to enter!
proxy.enter(new Wizard("Brown wizard")); // Brown wizard is not allowed to enter!
proxy.enter(new Wizard("Red wizard"));
proxy.enter(new Wizard("White wizard"));
proxy.enter(new Wizard("Black wizard"));
proxy.enter(new Wizard("Green wizard"));
proxy.enter(new Wizard("Brown wizard"));
```
Program output:
```
Red wizard enters the tower.
White wizard enters the tower.
Black wizard enters the tower.
Green wizard is not allowed to enter!
Brown wizard is not allowed to enter!
```
## Class diagram
![alt text](./etc/proxy.urm.png "Proxy pattern class diagram")
## Applicability
Proxy is applicable whenever there is a need for a more
versatile or sophisticated reference to an object than a simple pointer. Here
are several common situations in which the Proxy pattern is applicable
Proxy is applicable whenever there is a need for a more versatile or sophisticated reference to an
object than a simple pointer. Here are several common situations in which the Proxy pattern is
applicable.
* Remote proxy provides a local representative for an object in a different address space.
* Virtual proxy creates expensive objects on demand.
* Protection proxy controls access to the original object. Protection proxies are useful when objects should have different access rights.
* Protection proxy controls access to the original object. Protection proxies are useful when
objects should have different access rights.
## Typical Use Case
@ -136,7 +159,8 @@ are several common situations in which the Proxy pattern is applicable
* [java.lang.reflect.Proxy](http://docs.oracle.com/javase/8/docs/api/java/lang/reflect/Proxy.html)
* [Apache Commons Proxy](https://commons.apache.org/proper/commons-proxy/)
* Mocking frameworks Mockito, Powermock, EasyMock
* Mocking frameworks [Mockito](https://site.mockito.org/),
[Powermock](https://powermock.github.io/), [EasyMock](https://easymock.org/)
## Related patterns

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proxy/src/main/java/com/iluwatar/proxy/IvoryTower.java
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@ -27,7 +27,7 @@ import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* The object to be proxyed.
* The object to be proxied.
*/
public class IvoryTower implements WizardTower {