gaspersic/java-design-patterns
1
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

Update README.md

Browse Source
This commit is contained in:
Ilkka Seppälä
2020-08-29 22:13:55 +03:00
parent bc35911475
commit 67d1d16e1f
3 changed files with 77 additions and 39 deletions
Download Patch File Download Diff File Expand all files Collapse all files

44
object-pool/README.md
View File

@ -10,16 +10,18 @@ tags:
---
## Intent
When objects are expensive to create and they are needed only for
short periods of time it is advantageous to utilize the Object Pool pattern.
The Object Pool provides a cache for instantiated objects tracking which ones
are in use and which are available.
When objects are expensive to create and they are needed only for short periods of time it is
advantageous to utilize the Object Pool pattern. The Object Pool provides a cache for instantiated
objects tracking which ones are in use and which are available.
## Explanation
Real world example
> In our war game we need to use oliphaunts, massive and mythic beasts, but the problem is that they are extremely expensive to create. The solution is to create a pool of them, track which ones are in-use, and instead of disposing them re-use the instances.
> In our war game we need to use oliphaunts, massive and mythic beasts, but the problem is that they
> are extremely expensive to create. The solution is to create a pool of them, track which ones are
> in-use, and instead of disposing them re-use the instances.
In plain words
@ -27,11 +29,12 @@ In plain words
Wikipedia says
> The object pool pattern is a software creational design pattern that uses a set of initialized objects kept ready to use – a "pool" – rather than allocating and destroying them on demand.
> The object pool pattern is a software creational design pattern that uses a set of initialized
> objects kept ready to use – a "pool" – rather than allocating and destroying them on demand.
**Programmatic Example**
Here's the basic Oliphaunt class. These are very expensive to create.
Here's the basic `Oliphaunt` class. These giants are very expensive to create.
```java
public class Oliphaunt {
@ -60,7 +63,7 @@ public class Oliphaunt {
}
```
Next we present the Object Pool and more specifically Oliphaunt Pool.
Next we present the `ObjectPool` and more specifically `OliphauntPool`.
```java
public abstract class ObjectPool<T> {
@ -100,7 +103,7 @@ public class OliphauntPool extends ObjectPool<Oliphaunt> {
}
```
And finally here's how we utilize the pool.
Finally, here's how we utilize the pool.
```java
var pool = new OliphauntPool();
@ -113,11 +116,30 @@ And finally here's how we utilize the pool.
var oliphaunt5 = pool.checkOut();
```
Program output:
```
Pool available=0 inUse=0
Checked out Oliphaunt id=1
Pool available=0 inUse=1
Checked out Oliphaunt id=2
Checked out Oliphaunt id=3
Pool available=0 inUse=3
Checking in Oliphaunt id=1
Checking in Oliphaunt id=2
Pool available=2 inUse=1
Checked out Oliphaunt id=2
Checked out Oliphaunt id=1
Pool available=0 inUse=3
```
## Class diagram
![alt text](./etc/object-pool.png "Object Pool")
## Applicability
Use the Object Pool pattern when
* The objects are expensive to create (allocation cost)
* You need a large number of short-lived objects (memory fragmentation)
* The objects are expensive to create (allocation cost).
* You need a large number of short-lived objects (memory fragmentation).