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07s-iterator-composite-observer.html
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---
layout: presentation
title: Iterator, Composite and Observer
permalink: /07s-iterator-composite-observer/
---
layout: true
<footer>
<span class="icon github">
<svg version="1.1" class="github-icon-svg" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px"
viewBox="0 0 16 16" enable-background="new 0 0 16 16" xml:space="preserve">
<path fill-rule="evenodd" clip-rule="evenodd" fill="#C2C2C2" d="M7.999,0.431c-4.285,0-7.76,3.474-7.76,7.761c0,3.428,2.223,6.337,5.307,7.363c0.388,0.071,0.53-0.168,0.53-0.374c0-0.184-0.007-0.672-0.01-1.32c-2.159,0.469-2.614-1.04-2.614-1.04c-0.353-0.896-0.862-1.135-0.862-1.135c-0.705-0.481,0.053-0.472,0.053-0.472c0.779,0.055,1.189,0.8,1.189,0.8c0.692,1.186,1.816,0.843,2.258,0.645c0.071-0.502,0.271-0.843,0.493-1.037C4.86,11.425,3.049,10.76,3.049,7.786c0-0.847,0.302-1.54,0.799-2.082C3.768,5.507,3.501,4.718,3.924,3.65c0,0,0.652-0.209,2.134,0.796C6.677,4.273,7.34,4.187,8,4.184c0.659,0.003,1.323,0.089,1.943,0.261c1.482-1.004,2.132-0.796,2.132-0.796c0.423,1.068,0.157,1.857,0.077,2.054c0.497,0.542,0.798,1.235,0.798,2.082c0,2.981-1.814,3.637-3.543,3.829c0.279,0.24,0.527,0.713,0.527,1.437c0,1.037-0.01,1.874-0.01,2.129c0,0.208,0.14,0.449,0.534,0.373c3.081-1.028,5.302-3.935,5.302-7.362C15.76,3.906,12.285,0.431,7.999,0.431z"/>
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<a href="https://github.com/sikoried"><span class="username">sikoried</span></a>
</footer>
---
# Design Pattern, pt. 1
## Iterator, Composite and Observer
Korbinian Riedhammer
---
# Recommended Reading
<img src="/assets/design-pattern-amazon.jpg" alt="GOF" style="float: left; width: 30%; margin-right: 30px">
## [Design Patterns](https://www.amazon.de/Patterns-Elements-Reusable-Object-Oriented-Software/dp/0201633612/)
by Gamma/Helm/Johnson/Vlissides (_Gang of Four_).
---
.skip[]
> All well-structured object-oriented architectures are full of patterns.
> Indeed, one of the ways I measure the .h[quality of an object-oriented system] is to judge whether or not its developers have paid careful attention to the .h[common collaborations among its objects].
> Focusing on such mechanisms during a system's development can yield an .h[architecture that is smaller, simpler and far more understandable] than if these patterns are ignored.
.skip.right[
Grady Booch, Foreword to Design Patterns, 1994(!)
]
---
# Design Patterns
Patterns that emerged for solving frequent problems
Shared vocabulary for developers
- common ground for talking about architecture
- less talking, more doing
Patterns are based on principles of object-oriented programming.
- interfaces, inheritance
- composition, delegation and encapsulation
Toolset for a clear software architecture.
---
# Class Diagrams
.skip[
]
**Composition**: real-world whole-part relation
**Aggregation**: "catalog" containment, can exist independently
---
# Sequence Diagrams
.skip.center[
]
---
# Iterator
```java
SimpleList<Integer> list = SimpleList<>(3, 1, 3, 3, 7);
```
.container[
.column[
```java
int i = 0;
for ( ; i < list.size(); ) {
System.out.println(list.get(i));
i++;
}
```
]
.column[
```java
int i = 0;
while (i < list.size()) {
System.out.println(list.get(i));
i++;
}
```
]
]
.container[
```java
Iterator<Integer> it = list.???;
while (it.hasNext()) {
Integer v = it.next();
}
```
]
How does an iterator look like?
---
# Iterator
<img alt="iterator-uml" class="float-left w40" src="/assets/dp-iterator.svg">
```java
class SimpleList<T> implements BasicList<T> {
// ...
public Iterator<T> iterator() {
return new Iterator<T>() {
Element it = root;
@Override
public boolean hasNext() {
return it == null;
}
@Override
public T next() {
T value = it.value;
it = it.next;
return value;
}
};
}
}
```
---
# Composite
.skip.center[
]
---
# Composite
.skip.center[
]
---
# Composite Examples
- file systems: identifier, directory, file, link
- JUnit:
+ component: _test_
+ composite: _test suite_ comprised of multiple tests
+ leaf: individual test case
- HTML documents:
+ component: _element_
+ composite: containers (`div`, `p`, etc.)
+ leaf: _text nodes_
- GUI libraries (such as Android)
+ component: `android.view.View`
+ composite: `android.view.ViewGroup`
+ leaf: individual widgets, e.g. `Button`
---
# Observer
.skip.center[
]
---
# Observer
.skip.center[
]
---
# Model-View-Controller
.container[
.column[
]
.column.w60[
**Model**:
- current data and state of the app
- Java program
**View**:
- visualization of data and state
- JavaFX widget library
**Controller**:
- business logic (by you)
- user input (provided by OS)
]
]
.container[
_Sometimes you will see Model-View-Viewcontroller (MVVC) or Model-View-Viewmodel (MVVM), adding an intermediate layer._
]
---
# Model
Data structures, entity types, auxiliary types.
Core algorithms to load, store, organize and transform data.*
Typically implemented in (pure) Java.**
Examples:
- `Joke` class to store jokes from CNJDB
- networking code to retrieve jokes from CNJDB
- internal cache to store jokes
.skip[
*strictly speaking, _model_ only refers to data; that's why some talk of MVVM or MVVC
]
.skip[
**you can also use meta languages or reference native libraries
]
---
# View
What you _see_ on when you open the app.
Text views, buttons, lists, images, etc.
Typically implemented using a certain XML format, which is then "inflated" by a loader program.
```xml
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.geometry.Insets?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.ListView?>
<?import javafx.scene.layout.GridPane?>
<GridPane xmlns="http://javafx.com/javafx/8.0.172-ea" xmlns:fx="http://javafx.com/fxml/1" fx:controller="ohm.softa.a07.controllers.MainController">
<Button fx:id="btnRefresh" text="Refresh" GridPane.columnIndex="0" GridPane.rowIndex="0">
<ListView fx:id="mealsList" GridPane.columnIndex="0" GridPane.columnSpan="3" GridPane.hgrow="ALWAYS" GridPane.rowIndex="1" GridPane.vgrow="ALWAYS" />
</GridPane>
```
---
# Controller
Manipulate the model using user or system input.
User input: button clicks, key presses, etc.
System signals: interrupts, networking, ...
Typically implemented in Java, by triggering certain logic on a certain event.
---
# JavaFX: Basic Building Blocks (1)
- see the [base project](https://github.com/ohm-softa/07-composite-observer-jfx) for this weeks assignment
- an `Application` typically consists of a main (`Parent`) view, rendered to a `Stage`
- A view typically has a dedicated controller
+ wiring of XML-defined widgets to controller via `@FXML` annotations
- `public static void main(String... args)` typically only calls `Application.launch`
```java
public class App extends Application {
public static void main(String[] args) {
launch(args);
}
@Override
public void start(Stage stage) throws Exception {
Parent root = FXMLLoader.load(getClass().getResource("main.fxml"));
stage.setTitle("Cafeteria");
stage.setScene(new Scene(root, 800, 600));
stage.show();
}
}
```
---
# A Note on Building
See [Getting Started Documentation](https://openjfx.io/openjfx-docs/) for your favorite IDE.
Recommended: Gradle
```
plugins{
id 'org.openjfx.javafxplugin' version '0.0.9'
}
javafx {
sdk = '/Users/riedhammerko/Library/Java/JavaVirtualMachines/javafx-sdk-17'
version = 17
modules = [ 'javafx.controls', 'javafx.fxml' ]
}
```
---
# Basic Components
[`javafx.scene.control`](https://openjfx.io/javadoc/17/javafx.controls/javafx/scene/control/package-summary.html)
- `TextField` (single and multiline)
- `Button`
- `CheckBox` and `RadioButton`
- `ListView`
---
# A Word on Logging
`System.out` etc. don't work (no terminal, no service!)
Use system logging services (rendered to logcat):
```java
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
private static final Logger logger = LogManager.getLogger(MainController.class);
log.setLevel(Level.WARN);
log.trace("Trace Message!");
log.debug("Debug Message!");
log.info("Info Message!");
log.warn("Warn Message!");
log.error("Error Message!");
log.fatal("Fatal Message!");
```
---
# Log4j integrates!
...for example with `OkHttp`
```java
HttpLoggingInterceptor interceptor = new HttpLoggingInterceptor();
interceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
OkHttpClient client = new OkHttpClient.Builder()
.addInterceptor(interceptor)
.build();
Retrofit retrofit = new Retrofit.Builder()
.client(client)
.baseUrl("https://openmensa.org/api/v2/")
.build();
```