chain of responsibilityhttps://www.youtube.com/watch?v=jDX6x8qmjbACOMMANDhttps://www.youtube.com/watch?v=ea5onQBXzS8INTERPRETERhttps://www.youtube.com/watch?v=6CVymSJQuJEITERATORhttps://www.youtube.com/watch?v=QDhjo5Vu8k8MEDIATORhttps://www.youtube.com/watch?v=8URTwfrOpscMEMENTOhttps://www.youtube.com/watch?v=OfD9QBZ0QfcOBSERVERhttps://www.youtube.com/watch?v=YIX9Bkl3ZPESTATEhttps://www.youtube.com/watch?v=MGEx35FjBuoSTRATEGYhttps://www.youtube.com/watch?v=-NCgRD9-C6oTEMPLATE METHODhttps://www.youtube.com/watch?v=aR1B8MlwbRIVISITORhttps://www.youtube.com/watch?v=pL4mOUDi54o