单例模式，双重检验锁

package com.weather168.utils;import android.content.Context;import com.weather168.MainActivity;import net.tsz.afinal.FinalDb;public class FinalDbUtil {private static FinalDb finalDb = null;private FinalDbUtil() {}public static FinalDb getInstanceOfFinalDb(Context context) {if (finalDb == null) {synchronized (FinalDb.class) {if (finalDb == null) {finalDb = FinalDb.create(context, MainActivity.dbName,MainActivity.isDebug);}}}return finalDb;}}

private FinalDb db = FinalDbUtil.getInstanceOfFinalDb(WelcomeActivity.this);