How to execute TestNG test methods in sequence order using JAVA reflection

I have a @Test method(ParentClass) and named as mainTest, and had situation to call n number of @Test methods which is in another class(ClassA(test1,test2), ClassB(test3,test4)) files, and declared inside of the mainTest. When I execute the mainTest method It has to execute the @Test methods which is called inside of mainTest in sequence order using reflection. Can somebody give me any inputs?