局部變量-循環內定義變量,和循環外定義變量的問題

循環內定義變量,和循環外定義變量的問題

循環外定義變量 tempReportInfo

public ArrayList<ReportInfo> getAllReportInfos() {
        ArrayList<ReportInfo> reportInfos = new ArrayList<ReportInfo>();
        Cursor cursor = null;
        ReportInfo tempReportInfo = new ReportInfo();

        synchronized (helper) {
            if (!db.isOpen()) {
                db = helper.getWritableDatabase();
            }
            cursor = db.rawQuery("SELECT * FROM " + DBKeysName.TABLE_REPORT,
                    null);
            try {
                if (cursor != null) {
                    while (cursor.moveToNext()) {
                        tempReportInfo.setUserIds(cursor.getString(cursor
                                .getColumnIndex(DBKeysName.ROW_REPORT_USERID)));
                        tempReportInfo
                                .setStationName(cursor.getString(cursor
                                        .getColumnIndex(DBKeysName.ROW_REPORT_STATIONNAME)));
                        tempReportInfo.setTime(cursor.getString(cursor
                                .getColumnIndex(DBKeysName.ROW_REPORT_TIME)));
                        tempReportInfo.setLineId(cursor.getInt(cursor
                                .getColumnIndex(DBKeysName.ROW_REPORT_LINEID)));
                        tempReportInfo.setType(cursor.getInt(cursor
                                .getColumnIndex(DBKeysName.ROW_REPORT_TYPE)));
                        tempReportInfo.setRole(cursor.getInt(cursor
                                .getColumnIndex(DBKeysName.ROW_REPORT_ROLE)));
                        tempReportInfo.setFlag(cursor.getInt(cursor
                                .getColumnIndex(DBKeysName.ROW_REPORT_FLAG)));
                        reportInfos.add(tempReportInfo);
                    }
            }
            } catch (Exception e) {
                // TODO: handle exception
                e.printStackTrace();
            } finally {
                cursor.close();
            }

        }
        return reportInfos;

    }

上述例子得到的結果是,reportInfos添加的是數量為與數據表裡行數一樣的,但內容為數據表裡第一條數據.

循環內定義變量tempReportInfo

    public ArrayList<ReportInfo> getAllReportInfos() {
        ArrayList<ReportInfo> reportInfos = new ArrayList<ReportInfo>();
        Cursor cursor = null;
        synchronized (helper) {
            if (!db.isOpen()) {
                db = helper.getWritableDatabase();
            }
            cursor = db.rawQuery("SELECT * FROM " + DBKeysName.TABLE_REPORT,
                    null);

            try {
                if (cursor != null) {
                    while (cursor.moveToNext()) {
                        ReportInfo tempReportInfo = new ReportInfo();
                        tempReportInfo.setUserIds(cursor.getString(cursor
                                .getColumnIndex(DBKeysName.ROW_REPORT_USERID)));
                        tempReportInfo
                                .setStationName(cursor.getString(cursor
                                        .getColumnIndex(DBKeysName.ROW_REPORT_STATIONNAME)));
                        tempReportInfo.setTime(cursor.getString(cursor
                                .getColumnIndex(DBKeysName.ROW_REPORT_TIME)));
                        tempReportInfo.setLineId(cursor.getInt(cursor
                                .getColumnIndex(DBKeysName.ROW_REPORT_LINEID)));
                        tempReportInfo.setType(cursor.getInt(cursor
                                .getColumnIndex(DBKeysName.ROW_REPORT_TYPE)));
                        tempReportInfo.setRole(cursor.getInt(cursor
                                .getColumnIndex(DBKeysName.ROW_REPORT_ROLE)));
                        tempReportInfo.setFlag(cursor.getInt(cursor
                                .getColumnIndex(DBKeysName.ROW_REPORT_FLAG)));
                        reportInfos.add(tempReportInfo);
                    }
            } catch (Exception e) {
                // TODO: handle exception
                e.printStackTrace();
        } finally {
                cursor.close();
            }

        }
        return reportInfos;

    }

這樣才能得到想要的結果:reportInfos添加了數據表裡的所有數據.

請問一下,為什麼循環外定義變量tempReportInfo就得到不一樣的結果呢?

最佳回答：

放外面也行
但是需要每次循環都加上
tempReportInfo = new ReportInfo();

否則只創建了一個對象，你修改來修改去，添加到集合的都是指向同一個對象的引用