JavaFX how do I fix stream() - javafx

Question

I'm building Minesweeper following this video: https://www.youtube.com/watch?v=JwcyxuKko_M
But I need a MVC pattern for this and I'm stuck with a NullPointer here in the line with the stream in View:
public class View{
Model model;
Field f; //here's where I'm trying to access the List created in Field class
Stage primarystage;
Text number = new Text();
public View(Model model, Stage primaryStage){
this.model = model;
this.primarystage = primaryStage;
Pane root = new Pane();
root.setPrefSize(model.WIDTH, model.HEIGHT);
//iterate through rows and columns to fill board with random bombs
for (int y = 0; y < model.Y_FIELDS; y++) {
for (int x = 0; x < model.X_FIELDS; x++) {
Field field = new Field(x, y, Math.random() < 0.2);
model.array[x][y] = field;
root.getChildren().add(field);
}
}
for (int y = 0; y < model.Y_FIELDS; y++) {
for (int x = 0; x < model.X_FIELDS; x++) {
Field field = model.array[x][y];
//trying to access the method getSurrounding from class Field with f
long bombs = f.getSurrounding(field).stream().filter(b -> b.isBomb).count(); //number of bombs
if (bombs > 0)
field.bomb.setText(String.valueOf(bombs));
}
}
Scene scene = new Scene(root, model.getWidth(), model.getHeight());
getStage().setScene(scene);
}
Here's the Field class:
import javafx.scene.layout.StackPane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.scene.text.Text;
import java.util.ArrayList;
import java.util.List;
public class Field extends StackPane{
//information for each field: x coordinate, y coordinate, is it a bomb or not
int x;
int y;
boolean isBomb; //determines whether or not the field is a bomb
int bombsNum = 0; //counts how many bombs are surrounding the field
Model model;
Rectangle board = new Rectangle(model.FIELD_SIZE - 2, model.FIELD_SIZE - 2);
Text bomb = new Text();
public Field(int x, int y, boolean isBomb){
this.x = x;
this.y = y;
this.isBomb = isBomb;
board.setFill(Color.LAVENDER);
board.setStroke(Color.BLACK);
bomb.setText(isBomb ? "X" : "");
getChildren().addAll(board,bomb);
setTranslateX(x * model.FIELD_SIZE);
setTranslateY(y * model.FIELD_SIZE);
}
public List<Field> getSurrounding(Field field){
//looks at all the fields surrounding the current field
List<Field> surrounding = new ArrayList<>();
int[] coordinates = new int[]{
-1,-1, //top left field
-1, 0, //left field
-1, 1, //bottom left field
0,-1, //top middle field
0, 1, //bottom middle field
1,-1, //top right field
1, 0, //right field
1, 1 //bottom right field
};
for (int i = 0; i < coordinates.length; i++) {
int columnX = coordinates[i]; //considers the x coordinate of a surrounding field
int rowY = coordinates[++i]; //considers the y coordinate of a surrounding field
int newX = field.x + columnX; //sets the x coordinate of a surrounding field
int newY = field.y + rowY; //sets the y coordinate of a surrounding field
if (newX >= 0 && newX < model.X_FIELDS //make sure it's not out of bounds
&& newY >= 0 && newY < model.Y_FIELDS) {
surrounding.add(model.array[newX][newY]);
}
}
return surrounding;
}
}
And the Variables in Model:
public static final int FIELD_SIZE = 40;
public static final int WIDTH = 800;
public static final int HEIGHT = 600;
//sets number of fields in x and y axis
public static final int X_FIELDS = WIDTH / FIELD_SIZE;
public static final int Y_FIELDS = HEIGHT / FIELD_SIZE;
public Field[][] array = new Field[X_FIELDS][Y_FIELDS];
Why isn't it working? I'm trying to pass a list (containing all neighbors of a field) into the stream and filter for the ones containing bombs and then counts those bombs so I can display that number on the current field so the player will know. Why doesn't it recognize the list I passed? Or is it the filter that's confused? Thank you.
Exception in Application start method
Exception in thread "main" java.lang.RuntimeException: Exception in Application start method
at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:917)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$155(LauncherImpl.java:182)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
at View.<init>(View.java:46)
at Main.start(Main.java:10)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$162(LauncherImpl.java:863)
at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$175(PlatformImpl.java:326)
at com.sun.javafx.application.PlatformImpl.lambda$null$173(PlatformImpl.java:295)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$174(PlatformImpl.java:294)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)

Answer 1

I think you have a design problem in getSurrounding(). At the moment you require to pass a Field as an argument but as far as I understand this parameter is non-sense. When you want to grab the surroundings of a Field you don't need to provide another Field ! Just use the current one (this) !
public List<Field> getSurrounding() {
//looks at all the fields surrounding the current field
List<Field> surrounding = new ArrayList<>();
int[] coordinates = new int[]{
-1,-1, //top left field
-1, 0, //left field
-1, 1, //bottom left field
0,-1, //top middle field
0, 1, //bottom middle field
1,-1, //top right field
1, 0, //right field
1, 1 //bottom right field
};
for (int i = 0; i < coordinates.length; i++) {
int columnX = coordinates[i]; //considers the x coordinate of a surrounding field
int rowY = coordinates[++i]; //considers the y coordinate of a surrounding field
int newX = this.x + columnX; //sets the x coordinate of a surrounding field
int newY = this.y + rowY; //sets the y coordinate of a surrounding field
if (newX >= 0 && newX < model.X_FIELDS
&& newY >= 0 && newY < model.Y_FIELDS) {
surrounding.add(model.array[newX][newY]);
}
}
return surrounding;
}
Thefore the line that causes you problem at the moment can be changed to:
long bombs = field.getSurrounding().stream().filter(b -> b.isBomb).count();
It means you can get rid of the view attribute Field f because it is now unused. That was the reason why it was null because it had no purpose, therefore was never initialized.