JavaFX randomly fill ListViews - javafx

Question

I was trying to make a program where you can add names as CheckBoxes. By checking them and pressing the randomize button all the names would be placed in 2 different ListViews (each name can be placed only once and each ListView has to have the same number of names or 1 more name inside). I have no idea how it should be written in the "onRandom" section.
package sample;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.scene.control.Button;
import javafx.scene.control.CheckBox;
import javafx.scene.control.ListView;
import javafx.scene.control.TextField;
import javafx.scene.layout.VBox;
import java.util.Objects;
public class Controller {
#FXML
private Button add;
#FXML
private Button delete;
#FXML
private VBox vbox;
#FXML
private TextField text;
#FXML
private Button random;
#FXML
private ListView listview1;
#FXML
private ListView listview2;
#FXML
private CheckBox cb;
#FXML
void initialize() {
}
#FXML
public void onEnter(ActionEvent e){
CheckBox cb = new CheckBox(text.getText());
vbox.getChildren().add(cb);
if (text.getText().matches("")) {
vbox.getChildren().remove(cb);
}
}
#FXML
public void onAdd(ActionEvent e) {
CheckBox cb = new CheckBox(text.getText());
vbox.getChildren().add(cb);
if (text.getText().matches("")) {
vbox.getChildren().remove(cb);
}
}
#FXML
public void onDelete(ActionEvent e) {
vbox.getChildren().removeIf(child -> ((CheckBox) child).isSelected());
}
#FXML
public void onRandom(ActionEvent e) {
vbox.getChildren()
.stream()
.map(item -> (CheckBox) item)
.filter(item -> item.isSelected())
.filter(value -> Objects.nonNull(value))
.forEach(value -> {
listview1.getItems().add(value.getText());
listview2.getItems().add(value.getText());
});
}
}
This one below is just for testing.
.forEach(value -> {
listview1.getItems().add(value.getText());
listview2.getItems().add(value.getText());
});
Here is my FXML file https://pastebin.com/9v8e0c0Y

Answer 1

Use Collections.shuffle to create a random permutation of the list, then add the first half to one ListView and the rest to the other.
// do not use raw types
#FXML
private ListView<String> listview1;
#FXML
private ListView<String> listview2;
...
private final Random randomNumberGenerator = new Random();
List<String> items = new ArrayList<>(); // copy children to new list
// the following loop imho is easier to comprehend than the Stream implementation
for (Node child : vbox.getChildren()) {
CheckBox cb = (CheckBox) child;
if (cb.isSelected) {
items.add(cb.getText());
}
}
Collections.shuffle(items, randomNumberGenerator);
final int size = items.size();
final int half = size / 2;
// add first half to first ListView and second half to second ListView
listview1.getItems().setAll(items.sublist(0, half));
listview2.getItems().setAll(items.sublist(half, size));
Note that some of the method calls on Stream are actually unnecessary in your case:
.filter(value -> Objects.nonNull(value))
Checking for null is never necessary for the children list of a Parent. The list implementation prevents null from being inserted to that list. The previous filter whould have thrown a NPE in cases where that predicate yields false anyways. In cases where you do need a predicate like this, you can use a method reference to shorten the code:
.filter(Objects::nonNull)