Hi, everyone! Starting from this article, the editor will open a new column "Introduction to the Java Language", which will cover the three major parts of Java syntax, Java OOP, and Java advanced features at the beginning.
Program overview
Okay, let's get back to business. From the moment you read this article, you have opened the door of IT programming. Since then, the term program may change the trajectory of your future life. In the future, you will write a "perfect" program with high availability, high expansion and high security between the high-speed CPU in your brain and the high-speed operation of the CPU in your brain. [Future You] 
First, let’s take a look at the concept of programs. Programs have two meanings in the present century, namely, programs in life and programs in computers.
Procedures in
life Procedures in life: We are not unfamiliar with these scenes when we go to the bank to handle business, or ask for leave when we are at school, or go to reimbursement at work. We carry out the so-called processes and procedures (routines) step by step over and over again, and this is the procedure in life.
Programs
in computers Today in this century, you may have changed the name of programs in real life, such as processes or procedures. And the concept of program, more often you have put it in the APP on your mobile phone, or QQ on the computer. They are indeed programs, created and written by our future colleagues and predecessors. The process of writing these programs is called programming.
Teacher Cha has something to say: Software is not a program. Software is a larger concept than an application. Software is a complete collection of programs, data and related documents. Can be extended to read "Software Engineering Fourth Edition" by Zhang Haifan and Lu Yunxiang
But if you just understand the program this way, you can get a little pediatrics. The following [Baidu Encyclopedia] explains pretty well! A program is actually a collection of instructions.
What is an instruction? For example: I am a boss (not currently), and I have a female secretary (not currently). Every day my schedule or some tedious matters are handed over to my secretary to do, I tell the secretary to help me invite someone A guest, she just did it. I told the secretary to help me notify the department that the meeting is about to be held, and she will do the same. In this example, one thing the boss tells the secretary is an order, and the secretary is the person who receives the order and then executes it.
Switching to the concept of the computer world, we are called programmers/code farmers. If you want the secretaries of the computer to perform some operations, such as outputting some content on the screen or automatically drawing an image of Peppa Pig, etc., you need to give The computer gives instructions. Learning to program is just learning the process of giving instructions to the computer secretary. 
The relationship between program and program
From above, we understand the two meanings of program. Is there any relationship between them? In fact, most of the programs in the computer are due to certain processes/programs in reality, which are very troublesome, time-consuming or cause some waste of resources (paper). Therefore, with the help of computers, we humans will live in real life. These programs in the computer are shown as programs in the computer. For example: online registration, online shopping, online course selection, OA system, etc.
One sentence can explain this relationship: Our programming is to transplant real-life business programs to computers and express them in the form of computer instructions.
Programming language overview
After understanding the concept of the program, how do we tell the computer these program instructions? Tell me verbally? Brainwave communication? Obviously not, then we write natural language to tell the computer what to do? I'm sorry that the computer can't understand it, it can only understand binary (number system 0 1). The early computer practitioners were typing 0 1 to tell the computer what to do, but for us humans, this bunch of 0110 is too difficult to read, so in the later development, we used natural language to define some special grammars. , And then use a "translator" (compiler) to help us translate it to the computer, so that the computer can execute our instructions, and we can understand what we have written. The special syntax mentioned above is a programming language, also known as a computer language.
Mainstream
programming languages There are too many programming languages, and there are all kinds of definitions of grammar. This is also normal, as in today's world, natural languages are all weird. So we don't need to pay too much attention to the partial "small languages", but only need to pay attention to the protagonists in today's IT programming field. [See TIOBE]
The figure below is the statistics of well-known rankings. Similar websites include PYPL and so on. The TIOBE ranking is based on the number of experienced programmers, courses and third-party vendors on the Internet, and uses search engines (such as Google, Bing, Yahoo!), Wikipedia, Amazon, and YouTube to calculate ranking data, which only reflects a certain programming The popularity of a language does not indicate whether a programming language is good or not, or the amount of code written in a language.
The Past and Present of
Java The Birth of
Java Java is a high-level programming language launched in 1995 by SUN Microsystems (translated as Sun Microsystems in China). The picture below is one of the co-founders of Java: James Gosling (known as the father of Java). In 2009, Sun was acquired by Oracle, and Gosling resigned. So far, Gosling has joined Amazon AWS.
The picture below is the logo of Java (a cup of steaming coffee, there are rumors that Java is also named because the big guys love to drink coffee from Java, Indonesia). But how these two strands of steam are like the thin hair on the heads of big guys.
In April 1991, the Green Project led by Dr. James Gosling was launched. The purpose of this project was to develop a program architecture that could run on various consumer electronic products (such as set-top boxes, refrigerators, radios, etc.) . The product of this plan is the predecessor of the Java language: Oak (Oak). Oak was not considered a success in the consumer goods market at the time, but with the rise of the Internet trend in 1995, Oak quickly found the most suitable market for its development and transformed it into a Java language. [1]
The development
of Java The following figure shows the development process of Java. Focus on 1995, 1998, 2009 and mid-2013. Only by understanding its history can we better "talk and partner" with it.
On May 23, 1995, the Oak language was renamed Java, and the Java 1.0 version was officially released at the SunWorld conference. The Java language put forward the slogan "Write Once, Run Anywhere" for the first time.
On January 23, 1996, JDK 1.0 was released, and the Java language had the first official version of the operating environment. JDK 1.0 provides a purely interpreted Java virtual machine implementation (Sun Classic VM). Representative technologies of the JDK 1.0 version include: Java Virtual Machine, Applet, AWT, etc.
On December 4, 1998, JDK ushered in a milestone version of JDK 1.2, the project code is Playground (Arena), in this version, Sun split the Java technology system into 3 directions, respectively, for desktop application development J2SE (Java 2 Platform, Standard Edition), J2EE (Java 2 Platform, Enterprise Edition) for enterprise-level development, and J2ME (Java 2 Platform, Micro Edition) for mobile terminals such as mobile phones. There are many representative technologies in this version, such as EJB, Java Plug-in, Java IDL, Swing, etc., and for the first time in this version, the Java virtual machine has a built-in JIT (Just In Time) compiler (in JDK 1.2) There have been three virtual machines, Classic VM, HotSpot VM and Exact VM, among which Exact VM has only appeared on the Solaris platform; the latter two virtual machines have built-in JIT compilers, while the Classic VM in the previous version can only Use JIT compiler in the form of plug-in).
On April 27, 1999, the HotSpot virtual machine was released. HotSpot was originally developed by a small company called "Longview Technologies". Because of the outstanding performance of HotSpot, the company was acquired by Sun in 1997. When the HotSpot virtual machine was released, it was provided as an add-on program to JDK 1.2. Later, it became the default virtual machine for JDK 1.3 and all later versions of Sun JDK.
On February 19, 2009, the project code-named Dolphin (Dolphin) JDK 1.7 completed its first milestone version. According to the function plan of JDK 1.7, a total of 10 milestones have been set. The last milestone version was originally planned to end on September 9, 2010, but due to various reasons, JDK 1.7 could not be completed as planned. During the development of JDK 1.7, due to the successive quagmire in technical competition and commercial competition, the company's stock market value fell to only 3% of the peak period, and it has been unable to promote the development of JDK 1.7 according to the normal plan. In order to end the long-term "bounce" problem of JDK 1.7 as soon as possible, Oracle announced that it would implement the "Plan B" soon after acquiring Sun, which significantly cut the target of JDK 1.7, so as to ensure that the official version of JDK 1.7 can be released in July 2011. Released on time on the 28th. [1]
Java ME has been cold and has been taken over by Android, etc. I wonder if you have used old-fashioned mobile phones such as Nokia? Remember the Java 2D game?
Android (Andorid is not a programming language) Although Google officially listed Kotlin as an officially supported development language in 2017, Java is still its main development language. The reason is that there are a large number of Java APIs at the bottom of Android (can be extended to read Oracle and Google’s Lawsuit).
Java is not only a programming language, but also a technical system formed by a series of computer software and specifications. This technical system provides a complete support environment for software development and cross-platform deployment, and is widely used in embedded systems, Various occasions such as mobile terminal, enterprise server, mainframe, etc. Today, the Java technology system has attracted more than 9 million software developers, which is the world's largest software development team. There are billions of devices using Java, including more than 1.1 billion personal computers, 3 billion mobile phones and other handheld devices, a large number of smart cards, and a large number of set-top boxes, navigation systems and other devices. [1]