Suppose you need to write code for a program for group chat. Whenever a user will send a message then it will be delivered to all other participants in the chat. Any online user of the chat group can send and receive the message. Let's implement this case scenario using mediator design pattern.

Classes of the system is given below. But in the diagram some statements of the classes are deleted. Deleted parts are shown with red $"?"$ symbol in the diagram.

Match the deleted parts with the appropriate statements $($Note: Statements are also given in the figure$).$

a$-$ users: ArrayList User

b$-$ chat:Ichat

c$-$ user:User

a$-$ users: ArrayList$|-c,||-a||||||I-c,||-b,$III$-aI-a,||1-C,I-a,||-b,$III$-c$