Question

我做了2节课 Score和ScoreDataSource 我在ScoreDataSource#cursorToScore(Cursor cursor)中发现了一个错误（红色突出显示）。

这是我的完整代码

首先，Score.java：

public class Score {
private int correct_listening;
private int correct_reading;
private int correct_structure;
private int final_score;
private long id;
private int number;
private String userName;
private long user_id;

public Score(int number, long user_id, int correct_listening, int correct_structure, int correct_reading, int final_score) {
    this.number = number;
    this.user_id = user_id;
    this.correct_listening = correct_listening;
    this.correct_structure = correct_structure;
    this.correct_reading = correct_reading;
    this.final_score = final_score;
}

public long getId() {
    return this.id;
}

public void setId(long id) {
    this.id = id;
}

public long getUser_id() {
    return this.user_id;
}

public int getNumber() {
    return this.number;
}

public void setNumber(int number) {
    this.number = number;
}

public void setUser_id(long user_id) {
    this.user_id = user_id;
}

public int getCorrect_listening() {
    return this.correct_listening;
}

public void setCorrect_listening(int correct_listening) {
    this.correct_listening = correct_listening;
}

public int getCorrect_structure() {
    return this.correct_structure;
}

public void setCorrect_structure(int correct_structure) {
    this.correct_structure = correct_structure;
}

public int getCorrect_reading() {
    return this.correct_reading;
}

public void setCorrect_reading(int correct_reading) {
    this.correct_reading = correct_reading;
}

public int getFinal_score() {
    return this.final_score;
}

public void setFinal_score(int final_score) {
    this.final_score = final_score;
}

public String getUserName() {
    return this.userName;
}

public void setUserName(String userName) {
    this.userName = userName;
}

public String toString() {
    return this.number + ". " + this.userName + "  |  " + this.correct_listening + "  |  " + this.correct_structure + "  |  " + this.correct_reading + "  |  " + this.final_score;
}

public float calculateScore(int listeningScore, int structureScore, int readingScore) {
    return (float) Math.round((float) ((((listeningScore + structureScore) + readingScore) / 3) * 10));
}

}

其次，ScoreDataSource.java。我在Score score = new Score();

收到错误消息

public class ScoreDataSource {
private String[] allColumns;
private SQLiteDatabase database;
private MySQLiteHelper dbHelper;

public ScoreDataSource(Context context) {
    this.allColumns = new String[]{MySQLiteHelper.USER_ID, MySQLiteHelper.SCORE_USER_ID, MySQLiteHelper.SCORE_LISTENING_CORRECT, MySQLiteHelper.SCORE_STRUCTURE_CORRECT, MySQLiteHelper.SCORE_READING_CORRECT, MySQLiteHelper.SCORE_FINAL};
    this.dbHelper = new MySQLiteHelper(context);
}

public void open() throws SQLiteException {
    this.database = this.dbHelper.getWritableDatabase();
}

public void close() {
    this.database.close();
}

public List<Score> findAll() {
    List<Score> score = new ArrayList();
    Cursor cursor = this.database.query(MySQLiteHelper.TABLE_SCORE, this.allColumns, null, null, null, null, "final_score DESC");
    cursor.moveToFirst();
    while (!cursor.isAfterLast()) {
        score.add(cursorToScore(cursor));
        cursor.moveToNext();
    }
    cursor.close();
    return score;
}

public long count() {
    return DatabaseUtils.queryNumEntries(this.database, MySQLiteHelper.TABLE_SCORE);
}

public List<Score> findAll(long id) {
    List<Score> score = new ArrayList();
    Cursor cursor = this.database.query(MySQLiteHelper.TABLE_SCORE, this.allColumns, "_id = " + id, null, null, null, "final_score DESC");
    cursor.moveToFirst();
    while (!cursor.isAfterLast()) {
        score.add(cursorToScore(cursor));
        cursor.moveToNext();
    }
    cursor.close();
    return score;
}

public Score findFirst(long id) {
    Cursor cursor = this.database.query(MySQLiteHelper.TABLE_SCORE, this.allColumns, "_id = " + id, null, null, null, null);
    cursor.moveToFirst();
    Score scores = cursorToScore(cursor);
    cursor.close();
    return scores;
}

public Score cursorToScore(Cursor cursor) {
    Score score = new Score();//<-- error here
    score.setId(cursor.getLong(0));
    score.setUser_id(cursor.getLong(1));
    score.setCorrect_listening(cursor.getInt(2));
    score.setCorrect_structure(cursor.getInt(3));
    score.setCorrect_reading(cursor.getInt(4));
    score.setFinal_score(cursor.getInt(5));
    return score;
}

public long create(Score score) {
    return this.database.insert(MySQLiteHelper.TABLE_SCORE, null, putValuesToObject(score));
}

public int update(Score score) {
    return this.database.update(MySQLiteHelper.TABLE_SCORE, putValuesToObject(score), "_id = " + score.getId(), null);
}

public ContentValues putValuesToObject(Score score) {
    ContentValues values = new ContentValues();
    values.put(MySQLiteHelper.SCORE_USER_ID, Long.valueOf(score.getUser_id()));
    values.put(MySQLiteHelper.SCORE_LISTENING_CORRECT, Integer.valueOf(score.getCorrect_listening()));
    values.put(MySQLiteHelper.SCORE_STRUCTURE_CORRECT, Integer.valueOf(score.getCorrect_structure()));
    values.put(MySQLiteHelper.SCORE_READING_CORRECT, Integer.valueOf(score.getCorrect_reading()));
    values.put(MySQLiteHelper.SCORE_FINAL, Integer.valueOf(score.getFinal_score()));
    return values;
}

public int delete(long id) {
    return this.database.delete(MySQLiteHelper.TABLE_SCORE, "_id = " + id, null);
}

public int deleteAll() {
    return this.database.delete(MySQLiteHelper.TABLE_SCORE, "final_score > 0", null);
}

public void setDefaultData() {
}
}

Answer 1

Score score = new Score();

好吧，既然你正在调用Score类的无参数构造函数，那么你应该在Score类中创建这样的构造函数：

public Score() {
    ...
}

它不是由编译器生成的，因为您定义了另一个构造函数（public Score(int number, long user_id, int correct_listening, int correct_structure, int correct_reading, int final_score) {...}）。

Answer 2

您必须在Score.java
中添加此方法

public Score() {

}

Answer 3

替换此功能

public Score cursorToScore(Cursor cursor) {
    Score score = new Score();//<-- error here
    score.setId(cursor.getLong(0));
    score.setUser_id(cursor.getLong(1));
    score.setCorrect_listening(cursor.getInt(2));
    score.setCorrect_structure(cursor.getInt(3));
    score.setCorrect_reading(cursor.getInt(4));
    score.setFinal_score(cursor.getInt(5));
    return score;
}

使用此功能

public Score cursorToScore(Cursor cursor)
 {

Score score = new Score(cursor.getLong(0),cursor.getLong(1),cursor.getInt(2),cursor.getInt(3),cursor.getInt(4),cursor.getInt(5));//<-- error here

return score;

}

Answer 4

构造函数定义如何组合类的对象。

如果定义的类没有构造函数，则隐式生成默认的无参数构造函数，它将为所有属性分配默认值（对于字符串为null，对于基本int和long等为0）

一旦为类显式定义了构造函数，那么默认的无参构造函数就不复存在了。如果要复制默认的无参构造函数机制，则必须显式定义无参数构造函数

public Score() {    
}

我忘记了代码java中的内容吗？

4 个答案: