Introduction: The so-called basis, it is the lowest level of knowledge, experience prior to interview a very good interviewer, earnestness, told me that the original aim, once you have the foundation, all the problems will be solved.
(Because of the time, I just put together a little knowledge, I encountered the interview subject write the lower surface, for your reference)
1: The role of java in the final keyword
The final keyword can be used in three places. For the modification of class A, class attributes and methods.
The modified final keyword class can not be inherited, modified final keyword class attributes and class methods can not be overwritten (rewritten);
For the modified final keyword class property, the sub-class would not give him a re-assignment, if re-assignment error.
2: The difference between overloading (Overload) and rewritable (Override) of
(1) Method of overloading and rewriting are multi-state manner, except that it is implemented compile-time polymorphism, which polymorphism is achieved runtime.
(2) occurs in a heavy-duty class, the method of the same name if there are different list of parameters (parameters of different types and different number of parameters or both) is considered overloaded;
Overwriting occurs between the sub-class and the parent class, subclass override required to be rewritten is rewritten parent class method with the same list of method parameters, return type have compatible than the parent class is rewritten better access method , can not be declared more exceptions (Richter substitution principle) than the parent class overrides the method. Overload no special requirements for the return type, it can not be differentiated according to the type of return. (This link: https://blog.csdn.net/wintershii/article/details/80558739 )
3: The role of the static keyword
The static keyword There are two main effects:
First, a single memory space allocated for a particular data type or object, irrespective of the number of objects created.
Second, to achieve a method or property of an object not associated with the class
Specifically, in the Java language, there are four kinds of static usage: member variables, member methods, code block and inner class
4.hashMap underlying principle (hashTable difference)
New features of 5.java1.8
The difference 6.ArrayList and ArraySet
The operating principle of 7.SpringMvc
8. Multithreading
9. The difference between the abstract class interface
10.jvm
11.Oracle and mysql
Difference 12.count (1) and coung (*) of
13.mybatis cache mechanism
14.limit how to optimize the amount of data
15. Index
16. The red-black tree
17.AOP operating principle