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1. JavaSE basics

1. Java Object Oriented

What are the characteristics of object orientation and how to understand it?

1. Encapsulation only provides interfaces to the outside world and hides details
2. Inheritance allows the system or function to have a certain continuity
3. Polymorphism at compile time and polymorphism at runtime The polymorphism
   at runtime is as follows: When system A accesses the services provided by system B, system B has multiple ways to provide services, but everything is for system A. transparent.
   Another is: method override (override)
   when compiling polymorphism is expressed as : if method overload (overload)
   is the four major characteristics , adding " abstract "
   abstraction is to summarize the common characteristics of a class of objects to construct a class process, including data abstraction and behavioral abstraction.

   2. Why use clone?

   What is the difference between the process of creating an object and the process of cloning an object?

   5 ways to create objects in Java && The difference between the new keyword and the newInstance() methodhttps: //www.cnblogs.com/yunger/p/5793632.html

   3. The difference between && and &

   && is represented as: logical, short-circuit operator;
   why is it called short-circuit, because if the expression on the left of && is false, the expression on the right will be directly short-circuited, and no operation will be performed