04-OC attribute usage, automatic release pool, encapsulation and inheritance

When declaring object type attributes, you can solve the memory issue in setter (the old value of release and the new value of retain) and release the last retain in dealloc.

Attribute is the memory of the object.

Default type. The setter method directly assigns values without retain operations.

For some special object types, if you do not want to share an object with others, using copy will automatically create a new object .. NSString is read-only. All other objects use retain.

Non-atomic operations have poor security and high efficiency. nonatomic is generally used in ios development.

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To access instance variables

Is a relationship between classes.

Parent class (NSObject)