Context context or environment

1. Use a metaphor to explain the context:

(1) We compare context to a person's hands (A: it represents a feature of context and is unique; a person has only one hand and applies it.ProgramThe context corresponding to different objects at runtime is also unique)

(2) A pair of hands can use different tools to do a lot of work: for example, writing with a pencil, drawing with a colored pen, eating with chopsticks, working with a hoe, etc., here the pencil, color pen, chopsticks and hoes are many classes defined in context.

(3) No matter what tools he uses to work with each other, it must have the same behavior: Push, pull, drag, drag, etc. This behavior is a lot of common methods defined in context.