understanding netflow

assigning it a value of undefined (not the string "undefined")Undefined and parameter judgmentLet's look at a simple function: 123456 function bool(val){if(typeof val == ‘undefined‘){return true;}return !!val;} Is there a problem with this function? Yes, because typeof return undefined value there are two possible, one is passed in is undefined, there is no value. 12 alert(bool(undefined));//truealert(bool());//true Obviously, bool (undef

My understanding of the relationship between uml class diagrams and my understanding of uml class diagrams Relationship between uml class diagrams: Generalization is inheritance. An Implementation relationship is a class that implements another interface. Dependency is a class that uses another class. It is a usage relationship. In a service of this class, another class is needed for assistance. An associat

Python development [Article 1]: first understanding of Python and first understanding of python I. python Environment 1. Install Python Windows: 1, download installation package 2 https://www.python.org/downloads/3 2, installation 4 default installation path: C: \ python275 3. Configure environment variables 6. Right-click the computer and choose Properties> advanced system Settings> advanced> environment v

A deep understanding of Java reflection and a deep understanding of java To understand the principles of reflection, you must first understand what type information is. Java allows us to identify the object and class information at runtime, mainly in two ways: one is the traditional RTTI, which assumes that we already know all the types of information during compilation; the other is the reflection mechanis

Deep understanding of JAVA polymorphism principles and deep understanding of java Polymorphism I have always known what polymorphism is, and I often use polymorphism when coding, but I have never really understood what the underlying operating mechanism of polymorphism is like, write it down specially, and make progress together with all of you. I also hope you can guide and correct me. The concept of polym

Python decorator understanding, python decorator understanding 1. Functions of the decorator Add new functions for the decorated object without modifying the source code and calling method of the decorated object Principles: 1. Do not modify the source code of the decorated object2. Do not modify the call method of the decorated object Objectives: Add new features to the decorated object 2. Definition and

A deep understanding of Django's custom filters and a deep understanding of django Preface This article mainly introduces you to the Django custom filter and shares it for your reference. I will not talk much about it below. Let's take a look at the details: Filters and functions Django filters are essentially functions, but there are too many "functions". To show their uniqueness, designers think of a nam

Deep understanding of slicing principles and deep understanding of Slicing A data element is obtained by specifying the subscripts or by specifying the subscript range. This access sequence is called slice. In some cases, it is also called a shard. For details about how slice works, refer to my previous article: How slice works in Python. First, analyze the slice operation from the bottom layer:Internally,

Deep understanding of Java Virtual Machine-Chapter 3: deep understanding of Java Virtual Machine 1. Overview 2. Is the object dead? Reference Counter Add a reference counter to the object. When there is a reference, add 1 to the counter. When the reference is invalid, the counter minus 1. Objects whose counter is 0 at any time cannot be used again. If the object is a circular reference, it cannot be process

Deep understanding of Java Virtual Machine-Chapter 10-early (compilation phase) optimization, deep understanding of virtual machines Chapter 2 early (compilation period) Optimization Javac compilation process: 1. parsing and filling the symbol table process Lexical and syntax analysis converts the source code to a Token set. For example, the code "int a = B + 2" contains six tags: int a = B + 2 Fill

Inverse Polish algorithm ~ Simple understanding of stack, Polish algorithm understanding # Include 　　

Deep understanding of Java Virtual Machine _ Chapter 2 _ Reading Notes and deep understanding of virtual machines 1. Contents of this chapter: Overview Data Area During Running Program counters Java Virtual Machine Stack Local method Stack Java heap Method Area Runtime constant pool Direct Memory HotSpot virtual machine object discovery Object Creation Object Memory L

Understanding of JAVA programming ideas and understanding of JAVA programming ideas1) POP -- Process-oriented programming ):Process-oriented programming is a functional-centered way of thinking and organizing. It emphasizes the process of processing and processing system data, in program design, the function or process is the basic structure of the program. The system function is composed of a set of relate

Python-Understanding functions, python-Understanding FunctionsFunction Definition Def functionname (arg ): Suite Return [expression] 1. keywords used when def defines a function 2. functionname function name 3. The parameter name of the arg function. Different parameters are input, and the return value is also different. The function is implemented by passing parameters. 4. Suite is the code segment that im

Deep understanding of recursive functions, many misunderstandings, and deep understanding of Recursion I haven't been able to take notes for a long time. This time, sky (my nickname) will explain something to everyone. What's wrong with me?# Include Using namespace std;Void bin (const unsigned int I){If (I/2)Bin (I/2 );Cout }Int main (){Int;Cin>;Bin ();Cout Return 0;}This is a binary program for finding a

An advanced understanding of JavaScript objects and a comprehensive understanding of javascript To understand JavaScript objects, we can start with object creation, attribute operations, and object methods. To sum up, it includes the following modules: 1. Create an object 1.1 direct object volume The direct volume of objects is the easiest way to create objects. A ing table consists of several name/value pa

In-depth understanding of Android (2) -- Understanding JNI (medium) and androidjni in Android Sunshine Xiaoqiang participated in the CSDN blog Star Selection, If you think sunshine Xiaoqiang blog is helpful to you, vote for Xiaoqiang: http://vote.blog.csdn.net/blogstar2014/details? Username = lxq_xsyu # content In the previous article, we learned about the use of JNI in Android. In fact, JNI is a very early

Html semantic understanding and html semantic understanding 1. What is HTML semantics? Based on the structure of the content (content semantics), select the appropriate tag (Code semantics) to facilitate developers to read and write more elegant code while enabling browser crawlers and machines to parse it well. 2. Why semantics? In order to present a good content structure and code structure on the page

Deep understanding (function () {...}) (); and deep understanding of function 1. It is called an anonymous function that runs immediately (also called an immediate function) 2. When an anonymous function is enclosed and a bracket is added to it, this anonymous function can run immediately! It's amazing ~ 3. To use a function, we must first declare its existence. The most common method is to use a function s

In-depth understanding of ListView: Performance Optimization 1. in-depth understanding of listviewOne list shows three elements: 1. ListView: displays the view of the list; 2. Adapter: map data to ListView; 3. Data: The specific string, image, or other basic components to be mapped; 2. Optimization Principle: 1. Create only necessary view objects; How to load data with ListView: Call the getCount () functio