安卓在Java中使用静态工厂方法和常量进行泛化
在我的Android应用程序中,我有一些非常相似的类,我们把它们叫做FooA
和FooB
对于这些类中的每一个,我都有一个schema类,其中包含表FooASchema
和FooBSchema
列的常量:
public final class FooASchema {
public static final String TABLE_NAME = "foo_a_table";
public static final String COL_CATEGORY_ID = "category_id";
public static final String COL_PROPERTY_A = "property_a";
public static final String COL_PROPERTY_B = "property_b";
// COL_PROPERTY_C = ...
}
public final class FooBSchema {
public static final String TABLE_NAME = "foo_b_table";
public static final String COL_CATEGORY_ID = "category_id";
public static final String COL_OTHER_PROPERTY_A = "other_property_a";
// COL_OTHER_PROPERTY_B = ...
}
FooA
和FooB
都有一个静态工厂方法,使我能够使用Cursor
创建它们:
public static FooA from(Cursor cursor) {
int categoryId = cursor.getInt(cursor.getColumnIndex(FooASchema.COL_CATEGORY_ID));
String propertyA = cursor.getString(cursor.getColumnIndex(FooASchema.COL_PROPERTY_A));
String propertyB = cursor.getString(cursor.getColumnIndex(FooASchema.COL_PROPERTY_B));
// int propertyC = ...
return FooA(id, propertyA, propertyB, ...);
}
public static FooB from(Cursor cursor) {
int categoryId = cursor.getInt(cursor.getColumnIndex(FooBSchema.COL_CATEGORY_ID));
int otherA = cursor.getInt(cursor.getColumnIndex(FooASchema.COL_OTHER_PROPERTY_A));
// String otherB = ...
return FooB(id, otherA, otherB, ...);
}
最后,我有两个用于从表中检索数据的util类:
public final class FooAUtils {
public static ArrayList<FooA> getFooAs(Context context, int categoryId) {
ArrayList<FooA> fooAs = new ArrayList<>();
Cursor cursor = MyDbHelper.getInstance(context).getReadableDatabase.query(
FooASchema.TABLE_NAME,
null,
FooASchema.COL_CATEGORY_ID + "=?",
new String[] {String.valueOf(categoryId)},
null,
null,
null);
cursor.moveToFirst();
while (!cursor.isAfterLast()) {
fooAs.add(FooA.from(cursor));
cursor.moveToNext();
}
cursor.close();
return fooAs;
}
// ...
}
public final class FooBUtils {
public static ArrayList<FooA> getFooBs(Context context, int categoryId) {
ArrayList<FooB> fooBs = new ArrayList<>();
Cursor cursor = MyDbHelper.getInstance(context).getReadableDatabase.query(
FooBSchema.TABLE_NAME,
null,
FooBSchema.COL_CATEGORY_ID + "=?",
new String[] {String.valueOf(categoryId)},
null,
null,
null);
cursor.moveToFirst();
while (!cursor.isAfterLast()) {
fooBs.add(FooB.from(cursor));
cursor.moveToNext();
}
cursor.close();
return fooBs;
}
// ...
}
您可以看到FooA
相关类和FooB
相关类之间的大多数代码非常相似,尤其是在util类中,它们的代码几乎相同
我想尝试减少这种重复,我一直在尝试使用泛型(我读过关于它们的文章,但还没有在项目中使用它们)
例如,我希望能够有一个通用的util类。以下是我如何实现它的想法:
public final class FooUtils {
public static <T> get(Context context, int categoryId) {
ArrayList<T> items = new ArrayList<>();
Cursor cursor = MyDbHelper.getInstance(context).getReadableDatabase.query(
BaseSchema.TABLE_NAME,
null,
BaseSchema.COL_CATEGORY_ID + "=?",
new String[] {String.valueOf(categoryId)},
null,
null,
null);
cursor.moveToFirst();
while (!cursor.isAfterLast()) {
items.add(T.from(cursor)); // ??
cursor.moveToNext();
}
cursor.close();
}
// ...
}
其中:
public interface BaseSchema {
public static final String TABLE_NAME; // can't make this abstract?
public static final String COL_CATEGORY_ID = "category_id";
}
public final class FooASchema implements BaseSchema { ... }
public final class FooBSchema implements BaseSchema { ... }
但是正如你所看到的,我不能做T.from(cursor)
,我不能有一个抽象常量TABLE_NAME
子类可以实现
我如何以这种方式调用静态工厂方法
有没有更好的方法来解决这个问题并减少代码重复
共 (0) 个答案