Example contract class for a table which contains data about the store's headphones stock

StoreContract.java

public final class StoreContract {

    public static abstract class HeadphoneEntry implements BaseColumns {
      
        public static final String TABLE_NAME = "headphones";
        public static final String COLUMN_NAME = "name";
        public static final String COLUMN_PRICE = "price";
        public static final String COLUMN_STYLE = "style";
        public static final String COLUMN_IN_STOCK = "in_stock";
        public static final String COLUMN_DESCRIPTION = "description";
    
        /**
         * Possible values for the style of the headphone.
         */
        public static final int STYLE_EAR_BUD = 0;
        public static final int STYLE_ON_EAR = 1;
        public static final int STYLE_OVER_EAR = 2;
        public static final int STYLE_BONE_CONDUCTION = 3;

    }
}

BaseColumns implemented ? What is it : an interface, an abstract class, something else ?

I was wondering about the same thing. I found that it's an interface (see its code below) that has no methods. It just has two public constants: _ID and _COUNT.

==================================

  | * Copyright (C) 2006 The Android Open Source Project
  | *
  | * Licensed under the Apache License, Version 2.0 (the "License");
  | * you may not use this file except in compliance with the License.
  | * You may obtain a copy of the License at
  | *
  | * http://www.apache.org/licenses/LICENSE-2.0
  | *
  | * Unless required by applicable law or agreed to in writing, software
  | * distributed under the License is distributed on an "AS IS" BASIS,
  | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  | * See the License for the specific language governing permissions and
  | * limitations under the License.
  | */
package android.provider;

  public interface BaseColumns {
  /**
  * The unique ID for a row.
  *

Type: INTEGER (long)

  /
  public static final String _ID = "_id";
 
  /*
  * The count of rows in a directory.
  *

Type: INTEGER

  */
  public static final String _COUNT = "_count";
  }

==================================

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