JavaFX应用程序冻结，我不知道为什么

Question

So, I have made a Sudoku Solver as a project. The solving works fine except for one thing. When I insert numbers in positions i know will not work, the program freezes and crash. I think i've located the problem and it seems to be stuck in an infinite loop, but I can't figure out why?

Keep in mind that i'm new to JavaFX.

Any help is appreciated, thanks in advance.

The Sudoku Class

public class Sudoku {

private int board[][];

public Sudoku(){
    this.board = new int[9][9];
    clear();
    initBoard();
}

public void printBoard(){
    for(int i = 0; i < 9; i++){
        if((i % 3) == 0){
            System.out.print("-------------------------" + "\n");
        }
        for(int n = 0; n <9; n++){
            if((n % 3) == 0){
                System.out.print("| ");
            }
            System.out.print(board[i][n] + " ");
        }
        System.out.print("|" + "\n");
    }
    System.out.print("-------------------------");
}

public int getValueAt(int col, int row){
    return board[col][row];
}

public boolean solve(){
    if(solve(0,0)){
        return true;
    }else{
        clear();
        return false;
    }
}

public void clear(){
    for( int row = 0; row < 9; row++ ){
        for( int col = 0; col < 9; col++ ){              
            board[row][col] = 0 ;
        }           
    }
}

public void setBoard(int input[][]){
    clear();

    board = input;
}

private void initBoard(){
    clear();

    //Rad 1
    board[0][2] = 8;
    board[0][5] = 8;
    board[0][7] = 6;
    board[0][8] = 2;
    //Rad 2
    board[1][8] = 5;
    //Rad 3
    board[2][0] = 1;
    board[2][2] = 2;
    board[2][3] = 5;
    //Rad 4
    board[3][3] = 2;
    board[3][4] = 1;
    board[3][7] = 9;
    //Rad 5
    board[4][1] = 5;
    board[4][6] = 6;
    //Rad 6
    board[5][0] = 6;
    board[5][7] = 2;
    board[5][8] = 8;
    //Rad 7
    board[6][0] = 4;
    board[6][1] = 1;
    board[6][3] = 6;
    board[6][5] = 8;
    //Rad 8
    board[7][0] = 8;
    board[7][1] = 6;
    board[7][4] = 3;
    board[7][6] = 1;
    //Rad 9
    board[8][6] = 4;
}

private boolean solve(int i, int j){
    //Ifall en lösning har hittats
    if(i > 8){
        return true;
    }

    //Ifall positionen inte är satt
    if(board[i][j] != 0){
        //next(i, j);
        if(j < 8){
            if(solve(i, j+1)){
                return true;
            }
        }else{
            if(solve(i+1, 0)){
                return true;
            }
        }
    }
    //Ifall positionen är satt
    else{
        for(int n = 1; n < 10; n++){
            //Kollar ifall siffran "n" inte finns på någon av raderna
            if(rowIsOk(i, n) && colIsOk(j, n) && boxIsOk(i, j ,n)){
                board[i][j] = n;
                //next(i, j);
                if(j < 8){
                    if(solve(i, j+1)){
                        return true;
                    }
                }else{
                    if(solve(i+1, 0)){
                        return true;
                    }
                }
            }
        }
        board[i][j] = 0;
    }
    //board[i][j] = 0;
    return false;
}

//Kollar om raden är ok
private boolean rowIsOk(int row, int num){
    for(int i = 0; i < 9; i++){
        if(board[row][i] == num){
            return false;
        }
    }       
    return true;
}

//Kollar om kolumnen är ok
private boolean colIsOk(int col, int num){
    for(int i = 0; i < 9; i++){
        if(board[i][col] == num){
            return false;
        }
    }       
    return true;
}

private boolean boxIsOk(int row, int col, int num){
    row = (row/3) * 3;
    col = (col/3) * 3;

    for(int r = 0; r < 3; r++){
        for(int c = 0; c < 3; c++){
            if(board[row+r][col+c] == num){
                return false;
            }
        }
    }

    return true;
}

}

The GUI Class

import javafx.application.Application;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Alert;
import javafx.scene.control.Alert.AlertType;
import javafx.scene.control.Button;
import javafx.scene.control.TextField;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.TilePane;
import javafx.stage.Stage;

public class SudokuGUI extends Application{

private Sudoku sudoku = new Sudoku();
private TilePane board;

public static void main(String[] args){
    launch(args);
}

@Override
public void start(Stage primaryStage){
    primaryStage.setTitle("Sudoku Solver: H4xx0r Edition");

    BorderPane root = new BorderPane();
    board = initBoard();
    HBox control = addControl();

    root.setCenter(board);
    root.setBottom(control);

    primaryStage.setScene(new Scene(root, 500, 500));
    primaryStage.show();
}

private void updateBoard(TilePane tile){
    tile.getChildren().clear();
    for(int col = 0; col < 9; col++){
        for(int row = 0; row < 9; row++){
            tile.getChildren().add(createCell(col, row));
        }
    }
}

private TilePane initBoard(){
    TilePane tile = new TilePane();

    tile.setHgap(4);
    tile.setVgap(4);
    tile.setPadding(new Insets(0, 10, 0, 10));
    tile.setPrefColumns(9);
    tile.setPrefRows(9);
    //tile.setStyle("-fx-background-color: rgba(255, 215, 0, 0.1);");
    tile.setAlignment(Pos.CENTER);

    tile.getChildren().clear();
    for(int col = 0; col < 9; col++){
        for(int row = 0; row < 9; row++){
            tile.getChildren().add(createCell(col, row));
        }
    }

    return tile;
}

//Skapar "celler" med textfält
private TextField createCell(int col, int row){
    TextField txtfield = new TextField();
    String text;

    if(sudoku.getValueAt(col, row) != 0){
        text = Integer.toString(sudoku.getValueAt(col, row));
    }else{
        text = "0";
    }

    txtfield.setText(text);
    txtfield.setPrefWidth(45);
    txtfield.setPrefHeight(45);
    txtfield.setAlignment(Pos.CENTER);
    //txtfield.setEditable(false);
    txtfield.setStyle("-fx-font-weight: bold;");
    if(((row < 6 && row > 2) && (col < 6 && col > 2)) 
            || ((row < 3) && (col < 3)) //Vänster Upp 
            || ((row < 3) && (col > 5)) //Höger Upp
            || ((row > 5) && (col > 5)) //Höger Ner
            || ((row > 5) && (col < 3)))//Vänster Ner
    {   
        txtfield.setStyle("-fx-background-color: rgba(255, 178, 0, 0.9);" + "-fx-font-weight: bold;");
    }

    return txtfield;
}

//LÄgger till knappar i en Box
private HBox addControl(){
    HBox hbox = new HBox();
    Button solve = new Button("Solve");
    Button clear = new Button("Clear");
    Button set = new Button("Set");

    hbox.setPadding(new Insets(15, 12, 15, 12));
    hbox.setSpacing(10);
    hbox.setAlignment(Pos.BOTTOM_CENTER);

    solve.setPrefSize(100, 20);
    solve.setOnAction(e -> solve());
    clear.setPrefSize(100, 20);
    clear.setOnAction(e -> clear());
    set.setPrefSize(100,  20);
    set.setOnAction(e -> set());

    hbox.getChildren().addAll(solve, clear, set);

    return hbox;
}

//Knapp-funktioner
private void solve(){
    if(sudoku.solve()){
        updateBoard(board);
    }else{
        sudoku.clear();
        Alert alert = new Alert(AlertType.ERROR);
        alert.setTitle("YOLO SWAGGINS");
        alert.setHeaderText("Sudokut SWAG ERROR");
        alert.setContentText("Sudokut har inte tillräckligt med SWAG");     
    }
}

//Hämtar värden från textfälten
private void set(){
    int newset[][] = new int[9][9];
    int array[] = new int[board.getChildren().size()];

    for(int i = 0; i < board.getChildren().size(); i++){            
        TextField tmp = (TextField) board.getChildren().get(i);     
        //System.out.println(tmp.getText());
        array[i] = Integer.parseInt(tmp.getText());
    }

    int n = 0;
    for(int col = 0; col < 9; col++){
        for(int row = 0; row < 9; row++){
            newset[col][row] = array[n];
            n++;
        }
    }

    sudoku.setBoard(newset);
    updateBoard(board);
}

private void clear(){
    sudoku.clear();
    updateBoard(board);
}

}

Answer 1

The Problems seems to be that your solve(int i, int j) is called over and over again (recusive) which freezes the GUI if it does not find a solution. It seems that your algorithm is not well implemented.

Generally it is a good advise to execute computationally expensive code in a separate thread (ie not in the GUI-thread).