Shallow copy deep copy

Shallow copy ：

• For a data type is a member variable of a basic data type , The shallow copy will pass the value directly , That is to copy the attribute value to the new object .
• For a data type is a member variable that references a data type , Shallow copies are passed by reference , That is to say, only the reference value of the member variable （ Memory address ） Copy a copy to a new object .（ In fact, the member variable of both objects points to the same instance , under these circumstances , Modifying the member variable in one object affects the value of the member variable in another object ）
• Shallow copy is the default clone() Method to implement .

Deep copy ：

• Copy the member variable values of all basic data types of the object .
• Request storage space for all member variables that reference data types , And copy the object referenced by each reference data type member variable , Until all objects that the object can reach . in other words , To make a deep copy of an object, you need to copy the entire object .
• Realization way ：1. rewrite clone Method to achieve deep copy ;2. Deep copy through object serialization .