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08s-singleton-factory-strategy-command.html
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08s-singleton-factory-strategy-command.html
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---
layout: presentation
title: Singleton, Factory, Strategy, Command
permalink: /08s-singleton-factory-strategy-command/
---
layout: true
<footer>
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---
# Design Patterns, pt. 2
## Singleton, Factory
## Strategy, Command
Korbinian Riedhammer
---
# Singleton
---
# Singleton
Structure to enforce the use of a _unique_ instance.
---
# Strategy
---
# Strategy
---
# Strategy
```java
public class Kara extends JavaKaraProgram {
public static void main(String[] args) throws Exception {
Kara k = new Kara();
k.run("src/main/resources/world2.world");
}
@Override
public void myMainProgram() {
kara.move(); // one step forward
kara.turnLeft(); // you guessed it...
kara.turnRight(); // turn right
kara.treeFront(); // tree ahead?
kara.putLeaf(); // take a clover leaf
kara.removeLeaf(); // remove a clover leaf
}
}
```
How place leafs on every field?
---
# Strategy
Mechanism to provide different implementations to achieve the same outcome.
---
# Factory
---
# Factory
Composite pattern:
```json
{
"key": "value",
"nested": {
"key": "value"
}
}
```
```xml
<element>
<key>value</key>
<element>
<key>value</key>
</element>
</element>
```
---
# Factory
```java
interface Component {
String toString();
}
interface Composite extends Component {
void add(Component c);
}
interface Leaf extends Component {
}
```
```java
JsonComposite root = new JsonComposite("root");
root.add(new JsonLeaf("key", "value"));
Composite nested = new JsonComposite("nested");
nested.add(new JsonLeaf("key", "value"));
root.add(nested);
System.out.println(root);
// "root": {"key": "value", "nested": {"key": "value"}}
```
---
# Factory
Structure to enforce the use of abstract factories and products, by hiding the actual instantiation of the concrete factory and products.
---
# Command
---
# Command
.w40[
<img class="float-left" src="/assets/dp-command.svg">
]
Mechanism to organize, execute and undo operations on certain objects.