wpf C# interview reflection mvvm mvvm light interface generics arraylist hashtable using design patterns visitor template flyweight strategy memento mediator command wcf instance management application architecture ajax angularjs forms validations nested forms filters controllers directives bindings expressions ng-app ng-model environment setup threading synchronization rhino mocks test doubles oops app android linq testing nunit testcase typescript javascript abstract nodejs mysql CRUD dotnetcore mvc ftp python chmod linux golang variables uuid validator ExpressJS postgresql datatypes database