need help for project

class HighScore
        implements Serializable {
    private Score[] scores;
    
    HighScore() {
        this.scores = new Score[10];
    }
    
    addScore(final Score score) {
        Score swap = score;
        
        for (int s = 0;
                s < 10;
                s++) {
            if (swap.getScore() > this.scores[s].getScore()) {
                Score temp = this.scores[s];
                this.scores[s] = swap;
                swap = temp;
            }
        }
    }
    
    Score getScore(int score) {
        if (score < 0 || score > 9) {
            return null;
        }
        return this.scores[score];
    }
}

class Score
        implements Serializable {
    private final String user;
    private final int score;
    
    Score (final String user, final int score) {
        this.user = user;
        this.score = score;
    }
    
    String getUser() {
        return this.user;
    }
    int getScore() {
        return this.score;
    }
}

class Game {
    private HighScore highScore;

    void saveHighScore() {
        try { 
            FileOutputStream fos = new FileOutputStream("highScore.dat"); 
            ObjectOutputStream oos = new ObjectOutputStream(fos); 
            oos.writeObject(this.highScore); 
            oos.flush(); 
        } catch(IOException iex) {
            iex.printStackTrace();
        } finally {
            if (oos != null) {
                try {
                    oos.close();
                } catch(IOException iex) {
                    iex.printStackTrace();
                }
            }
        }
    }
    
    void loadHighScore () {
        try {
            FileInputStream fis = new FileInputStream("serial"); 
            ObjectInputStream ois = new ObjectInputStream(fis); 
            this.highScore = (HighScore)ois.readObject(); 
        } catch (IOException iex) {
            iex.printStackTrace();
            this.highScore = new HighScore();
        } catch (ClassNotFoundException cex) {
            cex.printStackTrace();
            this.highScore = new HighScore();
        } finally {
            if (ois != null) {
                try {
                    ois.close();
                } catch(IOException iex) {
                    iex.printStackTrace();
                }
            }
        }
    }
}