cannot resolve symbol "XXX"

I've been learning android for about a week and now I get stuck on creating database using SQLite in android. The compiler said that it cannot resolve symbol "TABLE_NAME". I trying to look around and figure out whats wrong with my code but failed to do so.Hope someone can help me to figuring out the problem.Thanks.

MyDatabaseHelper.java

package com.example.project.project.database;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

import com.example.project.project.TimeSheet;

public class MyDatabaseHelper extends SQLiteOpenHelper {
    public static final int DATABASE_VERSION=1;
    public static final String DATABASE_NAME="Company.db";
    public final static String TABLE_NAME="TimeSheet";
    public static final String ID="id";
    public static final String Name="name";
    public static final String Weather="weather";
    public static final String DATABASE_CREATE_TIME_SHEET="create table TimeSheet(id integer primary key autoincrement,name text not full, weather text not full);";
    public void onCreate(SQLiteDatabase db)
    {
        db.execSQL(DATABASE_CREATE_TIME_SHEET);
    }

    public void onUpgrade(SQLiteDatabase db, int oldVersion,int newVersion)
    {
        Log.w(MyDatabaseHelper.class.getName(),"Upgrading database from version"+oldVersion+"to"+newVersion+",which will destroy all old data");
        db.execSQL("Drop TABLE IF EXISTS TimeSheet");
        onCreate(db);
    }

    public MyDatabaseHelper(Context context)
    {
        super(context, DATABASE_NAME,null,1);
    }
}

TimeSheetAPI.java

package com.example.project.project.API;

import android.database.sqlite.SQLiteDatabase;
import com.example.project.project.database.MyDatabaseHelper;
import android.content.Context;
import android.database.SQLException;
import android.content.ContentValues;

public class TimeSheetAPI {
    private SQLiteDatabase database;
    private MyDatabaseHelper dbHelper;
    public String[] allColumns={MyDatabaseHelper.ID,MyDatabaseHelper.Name,MyDatabaseHelper.Weather};

    public TimeSheetAPI(Context context)
    {
        dbHelper=new MyDatabaseHelper(context);
    }

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

    public void close() {
        dbHelper.close();
    }
public long insertTimeSheet(String id,String name,String weather)
{
    ContentValues values=new ContentValues();
    values.put(MyDatabaseHelper.ID,id);
    values.put(MyDatabaseHelper.Name,name);
    values.put(MyDatabaseHelper.Weather,weather);
    return database.insert(TABLE_NAME,null,values); // cannot resolve symbol TABLE_NAME!!!
}

}