Abiturklassen NRW

In North Rhine-Westphalia the Zentralabitur in computer science comes with its own classes: List, Queue, Stack, BinaryTree, BinarySearchTree, ComparableContent, Graph, Vertex, Edge, DatabaseConnector and QueryResult. Students work with them throughout the Oberstufe, and they are the classes the Abitur tasks are written against.

You can use them together with Scratch for Java. The Abiturklassen then hold the sprites of your game, for example all the enemies on the stage in a List.

Two versions of Scratch for Java

Scratch for Java comes in two versions. They differ in three methods, which hand you a list of sprites:

Everything else is the same in both. If your course uses the Abiturklassen, take the NRW version from the Download page.

Setting up a project

1. Download scratch-<version>-nrw-all.jar from the Download page and add it to your project, the same way as described in Setup. In BlueJ, for example, put it into the +libs folder of your project.
2. Get the Abiturklassen. QUA-LiS NRW publishes them on the Lehrplannavigator as Implementationen von Klassen für das Zentralabitur ab 2018 (ZIP). Your teacher may also hand them out.
3. Copy the .java files you need into your project, next to your own classes. List.java is the one Scratch for Java needs. Take the others as your course uses them. Graph.java needs List.java, and DatabaseConnector.java needs Queue.java and QueryResult.java.

A BlueJ project then looks like this:

MeinSpiel/
  +libs/
    scratch-<version>-nrw-all.jar
  List.java           <- from the Abiturklassen
  Queue.java          <- from the Abiturklassen, if you use it
  MyStage.java        <- your classes
  Gegner.java
  Muenze.java

Do not put the Abiturklassen into a package, and do not put them into +libs. They have to sit next to your own classes. Do not change the files either. Use them exactly as they come.

Using the List

With the NRW version, write the Abitur's List on the left, and the sprites come back in it.

In a stage, find gives you all sprites of one class:

List<Gegner> gegner = find(Gegner.class);
gegner.toFirst();
while (gegner.hasAccess()) {
  gegner.getContent().changeY(-5);
  gegner.next();
}

getAll gives you every sprite on the stage:

List<Sprite> alle = getAll();
alle.toFirst();
while (alle.hasAccess()) {
  alle.getContent().hide();
  alle.next();
}

In a sprite, getTouchingSprites gives you the sprites it is touching right now:

List<Muenze> muenzen = getTouchingSprites(Muenze.class);
muenzen.toFirst();
while (muenzen.hasAccess()) {
  getStage().remove(muenzen.getContent());
  muenzen.next();
}

Each call returns a new list. Adding to it or removing from it does not add sprites to the stage or remove them. Use add and remove on the stage for that, as in the last example.

Using the other Abiturklassen

The other Abiturklassen need nothing special. Create them yourself and put sprites into them like any other object. A Queue lets enemies take turns, for example:

Queue<Gegner> warteschlange = new Queue<>();
 
List<Gegner> gegner = find(Gegner.class);
gegner.toFirst();
while (gegner.hasAccess()) {
  warteschlange.enqueue(gegner.getContent());
  gegner.next();
}
 
// later, whenever it is the next enemy's turn
Gegner amZug = warteschlange.front();
warteschlange.dequeue();
amZug.move(20);
warteschlange.enqueue(amZug);

How it works

The Abiturklassen are not part of Scratch for Java. The NRW version only expects a class called List in your project. Whenever find, getAll or getTouchingSprites is called, it looks that class up, creates an empty list with new List(), adds the sprites with append, and hands the list to you.

That is why List.java has to be in your project, and why it works with the files exactly as QUA-LiS publishes them. It is always your copy of the Abiturklassen that is used, never a different one.

Troubleshooting

incompatible types: java.util.List<…> cannot be converted to List<…>

You are using the normal JAR. Replace it with scratch-<version>-nrw-all.jar.

There is no class List in your project.

List.java is missing, is in a package, or is in +libs. Copy it next to your own classes.

var does not work

var gegner = find(Gegner.class); does not tell Java which list you want. Write the type out: List<Gegner> gegner = find(Gegner.class);.

The examples in the reference do not compile

The examples in the reference are written for the normal version, for example find(Coin.class).size(). With the NRW version, walk through the list with toFirst, hasAccess and next instead.

Using the Abiturklassen with the normal version

You can also keep the normal JAR and still use the Abiturklassen for everything else. Then find, getAll and getTouchingSprites return Java's list. The name List means the Abitur's list, so write Java's list with its full name:

java.util.List<Gegner> gegner = find(Gegner.class);
for (Gegner g : gegner) {
  g.hide();
}