java - 为什么我收到死代码警告？

Question

在将数据输入 sqlite 数据库之前，我想检查项目 ID 是否存在。但是，我从这些行中得到了死代码。这是什么原因？

死代码:

if (checkQuery == null) {
    ContentValues values = new ContentValues();
    values.put(KEY_IID, item.getIID()); // mysql item id
    values.put(KEY_NAME, item.getName()); // item name
    values.put(KEY_PRICE, item.getPrice()); // item price
    values.put(KEY_CREATED_AT, item.getDate()); // Created At
    values.put(KEY_TYPE, item.getType()); // type

    // Inserting Row
    db.insert(TABLE_ITEM, null, values);
    db.close(); // Closing database connection
    } 

数据库处理类:

public class DatabaseHandler extends SQLiteOpenHelper {

// All Static variables
// Database Version
private static final int DATABASE_VERSION = 2;

// Database Name
private static final String DATABASE_NAME = "itemManager";

// table name
public static final String TABLE_ITEM = "item";

// item Table Columns names
private static final String KEY_ID = "id";
private static final String KEY_IID = "iid";
private static final String KEY_NAME = "name";
private static final String KEY_PRICE = "price";
private static final String KEY_CREATED_AT = "created_at";
private static final String KEY_TYPE = "type";

public DatabaseHandler(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
}

// Creating Tables
@Override
public void onCreate(SQLiteDatabase db) {
    String CREATE_ITEM_TABLE = "CREATE TABLE " + TABLE_ITEM + "("
            + KEY_ID + " INTEGER PRIMARY KEY autoincrement,"
            + KEY_IID + " INTEGER"
            + KEY_NAME + " TEXT,"
            + KEY_PRICE + " TEXT,"
            + KEY_CREATED_AT + " TEXT,"
            + KEY_TYPE + " TEXT" + ")";
    db.execSQL(CREATE_ITEM_TABLE);
}

// Upgrading database
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    // Drop older table if existed
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_ITEM);

    // Create tables again
    onCreate(db);
}

/**
 * Storing item details in database
 * */
public void addItem(Items item) {
    String checkQuery = "SELECT iid FROM item WHERE iid = KEY_IID";
    SQLiteDatabase db = this.getWritableDatabase();

    if (checkQuery == null) {
    ContentValues values = new ContentValues();
    values.put(KEY_IID, item.getIID()); // mysql item id
    values.put(KEY_NAME, item.getName()); // item name
    values.put(KEY_PRICE, item.getPrice()); // item price
    values.put(KEY_CREATED_AT, item.getDate()); // Created At
    values.put(KEY_TYPE, item.getType()); // type

    // Inserting Row
    db.insert(TABLE_ITEM, null, values);
    db.close(); // Closing database connection
    } else {
        Log.d("notice", "item already in watchlist");
        db.close();
    }  
}

/**
 * Getting item data from database
 * */
public List<Items> getAllItems(){
    List<Items> itemList = new ArrayList<Items>();
    String selectQuery = "SELECT  * FROM " + TABLE_ITEM;

    SQLiteDatabase db = this.getWritableDatabase();
    Cursor cursor = db.rawQuery(selectQuery, null);
    // Move to first row
    if (cursor.moveToFirst()) {
        do {
            Items item = new Items();
            item.setID(Integer.parseInt(cursor.getString(0)));
            item.setName(cursor.getString(1));
            item.setPrice(cursor.getString(2));
            item.setDate(cursor.getString(3));
            item.setType(cursor.getString(3));
            // Adding item to list
            itemList.add(item);
        } while (cursor.moveToNext());
    }

    // return item list
    return itemList;
}

/**
 * return true if rows are there in table
 * */
public int getRowCount() {
    String countQuery = "SELECT  * FROM " + TABLE_ITEM;
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.rawQuery(countQuery, null);
    int rowCount = cursor.getCount();
    db.close();
    cursor.close();

    // return row count
    return rowCount;
}

 // Updating item
public int updateItem(Items item) {
    SQLiteDatabase db = this.getWritableDatabase();

    ContentValues values = new ContentValues();
    values.put(KEY_NAME, item.getName());
    values.put(KEY_PRICE, item.getPrice());
    values.put(KEY_CREATED_AT, item.getDate());
    values.put(KEY_TYPE, item.getType());

    // updating row
    return db.update(TABLE_ITEM, values, KEY_ID + " = ?",
            new String[] { String.valueOf(item.getID()) });
}

// Deleting item
public void deleteItem(Items item) {
    SQLiteDatabase db = this.getWritableDatabase();
    db.delete(TABLE_ITEM, KEY_ID + " = ?",
            new String[] { String.valueOf(item.getID()) });
    db.close();
}
}

Answer 1

String checkQuery = "SELECT iid FROM item WHERE iid = KEY_IID";
SQLiteDatabase db = this.getWritableDatabase();

if (checkQuery == null) {

checkQuery 永远不能为 null，因为您在 if-check 上方 2 行对其进行了初始化...因此永远不会调用 if-clause 中的代码。