The performance of the stage actors is still a function of the interface type array.

The Perform method in the performer interface is critical.

Program object Creation (there is an array declaration in the program class, and the constructor adds an array of performer interface types and puts 3 performers into the array,

3 performers have implemented different perform methods in the interface perform. Some sing, some dance ... Some drumming ...

Loop through the lineup in method show. Then perform different perform performances in the order in which they were assigned.

The performance of the stage actors is still a function of the interface type array.