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Java basics --- Servlet filter, basics --- servlet Servlet filters are literally understood as landscape-level filtering to meet the requirements of use. In fact, Servlet filters are the middle layer components of server and client requests and responses, in actual project development, Servlet filters are mainly used to filter browser requests and forward filtered requests to the next resource. Basic concep

Java basics-enumeration details, java basics Enumeration Before JDK1.5, JAVA can define new types in two ways: classes and interfaces. For most object-oriented programming, it seems sufficient to have these two types, but it is not suitable in some special cases. For example, if you want to define a Color class, it can only have three types of Red, Green, and Blue, and other values are incorrect, the enumer

Python basics document string, python basics tutorial String formatting String formatting is implemented using the string formatting operator % Percent. Place a string (formatted string) on the left side of %, and put the value to be formatted on the right side. You can use a value, such as a string or number, you can also use tuples or dictionaries with multiple values, such >>> Print "hello. % s. % s e

Java basics and java Basics In object-oriented programming languages, classes are first-class citizens, and the entire system is composed of classes. Methods in Java cannot exist independently. All methods must be defined in the class. classes or objects must be used as callers for executing methods. The Java language is a static language. After a class is defined, as long as the class file is not re-comp

MySQL BASICS (optimization) and mysql Basics 1. When creating a table, we can set the field width in the table as small as possible to achieve better performance. 2. When possible, set the field to not null as much as possible, so that the database does NOT need to compare NULL values during future query execution. 3. For some text fields, such as "Province" or "gender", we can define them as the ENUM type.

SQL basics 1: SQL Basics 1. What is SQL? SQL is a structured query language. SQL enables us to access databases SQL is an ANSI standard computer language. Ii. What can SQL do? SQL queries for Databases SQL can retrieve data from the database SQL inserts new records into the database SQL updates database data SQL can delete records from the database SQL allows you to create a new database. SQL a

Java basics 6: java BasicsJava basics 61 and javadoc1.1 usage Usage: javadoc [options] [packagenames] [sourcefiles] [@ files] 1.2 instance 1.3 Note To be docized, it must be a public class) Ii. classpath A reference to the classpath variable Iii. Singleton Design Model Iv. inherit the benefits of inheritance 4.1 4.2 Inheritance System 4.3 this and super Super is not a reference

Python basics and python Basics List (similar to array)Note:Any types of elements can exist in the same list.table = ["1","2","3"]; Access the last element:table[-1], Second to lasttable[-2]And so on. Add ElementAdd (append) at the end of the list)table.append(var);Insert an element anywhere)table.insert(index,var);// Add the element var to make its subscript index; Delete an element (del) Sort

JAVA basics 2. java Basics 2.1 keywords Common keywords include: 　　 2.2 identifier In short, an identifier is actually a symbol used to identify something. 　　 2.3 annotation Application Description 　　 Comment: 　　 Annotation application: 　　 2.4 constants and variables Definition and classification of constants 　　 Origin of hexadecimal 　　 Note: byte is 1 byte = 8 binary bits, 1 K = 1024. Basic conversion

Python Study Notes 1-basics and python Study Notes Basics 1) annotations A single line comment starts with #. For example: # The first comment Multi-line comments can contain multiple # numbers, including ''' and "", for example: # Comment on the first line # Comment on the second line ''' Comment on the third line Comment on the fourth line ''' """ Comment on the fifth line Line 6 comment """ 2) lines and

Java basics --- memory analysis, java basics --- Java concurrency isShared Memory Model(Rather than the message passing model), the common state of the program is shared between threads, and the public state in the write-Read Memory is used between threads.ImplicitProceedCommunication. Data Interaction cannot be directly transmitted between multiple threads. Interaction between threads can only be achieved

Java basics 18 and java basics 18 Import java. util. sums; public class Eightheen {/* determines whether a prime number can be divisible by several 9 */public static void main (String [] args) {sums input = new sums (System. in); System. out. println ("enter a prime number:"); int a = input. nextInt (); int B = 9, I = 0; if (judge (a) = 0) {while (B %! = 0) {B = B * 10 + 9; I ++;} System. out. println (a +

Java basics --- reflection mechanism, java basics ---1. Is java a Dynamic Language? Generally speaking, dynamic language means that the program structure or variable type can be changed while the program is running. From this point of view, JAVA and C ++ are not dynamic languages. But JAVA has a very prominent Dynamic correlation mechanism: reflection. Through reflection, Java can load, explore, and use cla

Python BASICS (6): List and metadata, and python Basics I. List The list is a container where a group of data can be placed, and each element in the list has a location index. Each element in the list can be changed. operations on the list will affect the original list. The definition of the List is defined by "[]". elements are separated by commas (,), for example: a = [12,'hello',15.5,True] A list is defi

Python BASICS (4): Conditions and loops, python Basics In actual development, if you want to implement certain functions or requirements, some logic is involved, complicated or simple. How can you implement the python syntax? This involves conditions and loops. Obviously, most languages have conditional and cyclic syntaxes, and python syntaxes are similar to them. It is easy to learn, and students with basi

Python BASICS (10)-numbers, python basics-Numbers The topic of this article is numbers in Python. Describes each numeric type in detail, the various operators they apply, and the built-in functions used to process numbers. At the end of the article, I briefly introduced several modules used to process numbers in the standard library. URL: http://www.cnblogs.com/archimedes/p/python-number.html.Numeric type N

Java programming basics-Fibonacci series and programming Basics Problem description: A frog can jump to level 1 or Level 2 at a time. Find the total number of hops that the frog jumps to an n-level step. Thought: possible situations: (1) n = 1, one method; (2) n = 2, two methods; (3) for level n, only jump from level n-1 or level N-2, so draw the conclusion: | 1, (n = 1) F (n) = | 2, (n = 2)| F (n-1) +

Java concurrency basics and java concurrency Basics Concurrency is the ability to run multiple programs in parallel or run multiple parts of a program in parallel. If a time-consuming task in a program can be run asynchronously or in parallel, the throughput and interactivity of the entire program will be greatly improved. Modern PCs have multiple CPUs or one CPU has multiple cores. Whether multi-core capab

Java basics --- XML parsing (1), basics --- xmlXML is a scalable Markup Language In the XML file, because more information is described, you should use the definition name of the element installed in the program to remove the corresponding content after obtaining an xml file, such an operation is called XML parsing. In XML parsing, W3C defines the parsing methods of the SAX and DOM. program operations of th

Learning mysql syntax-basics (1), mysql syntax-Basics PrefaceMysqlMysql syntax-This article uses Navicat Premium (Database Management Tool) to connect to mysql data.This article mainly consists of two parts:1. Create a user, create a database, assign permissions to the user, and delete user permissions.Ii. Common Data Types in MYSQLIii. Table-create a table, primary key, and foreign keyIv. Three paradigms