Java notes: Part 2: Java environment first, part 2

Java notes: Part 2: Java environment first, part 2

# Routine nagging 1 # Java Development History in the previous article can actually summarize a bowl of chicken soup. If you are rich, you cannot masturbate. If you are poor, you cannot change your money. (Haha, I am so talented! However, this sentence seems to have been heard)

# Routine nagging 2 # Some people say that I didn't write the difference between process-oriented and object-oriented, which will be written in Java object-oriented later.

Java, like other advanced languages, isMultiple features,Multiple FunctionsIn addition to a wide variety of class libraries, Java also provides three versions (specifically, they are a combination of three different class libraries:

JavaEE(Old Name:J2EE, Full name: Java 2 Enterprise Edition), is a version positioned on the server, there are a lot of server support.

JavaSE(Old Name:J2SEJava 2 Standard Edition is a version located on a personal computer. It has many support for file processing and graphic interfaces.

JavaME(Old Name:J2EEJava 2 Micro Edition is a version positioned on consumer electronic products. (Do you still remember what we said before about the Green Project, the predecessor of Java ?).

The three Java versions add up to almost cover the entire computer science (no hardware processing), which makes us suspect in our lives ...... (To cheer you up, Java's implementation in some aspects is tricky and not very detailed)

At the same time, Java has three different environments (why are they all 3? How did I think of something ......) :

JDK(Full name: Java Development Kit), Java integrated Development environment, also known as Java Development Kit

JRE(Full name: Java Runtime Environm), Java Runtime Environment, as long as you have this environment, you can run the Java program on the computer (here I will talk about it again, people who have played in my world, you have installed JRE in Java. Java runtime environments cannot be programmed in Java, so you cannot write MOD and servers. Therefore, if you are interested, go to the next JDK, as described below)

JVM(Full name: Java Virtual Machine), Java Virtual Machine (in fact, this is a half environment), a Virtual computer used to execute bytecode (bytecode) (computer, you have not read the error ), the Java code we write is run on JVM. JVM is also a specification. Of course, we can also write this specification (write a virtual computer, it's so cool !), It can also be implemented through hardware (have you ever heard of a Java chip ?). At the same time, JVM is also a cross-platform Java Implementation. By writing different JVMs, the code can run everywhere (to put it bluntly, JVM is a computer dedicated to running Java, I can run Java programs wherever he is put ).

In addition, the three environments of Java are nested layer by layer and belongInclusion relationship(JDK includes JRE and JRE includes JVM), so with JDK, there are three environments.

After talking about so many theories, we can finally start a pleasant Java programming (but tomorrow). Now let's prepare for Java programming and download Java. But we are also people who have learned the Java theory. We cannot talk about downloading Java to those who are playing in my world. What should we say? Let's think about it. Let's look at it later. Download the JDK of JavaSE (to explain: we are now a beginner programming, and we are running on our own computer, so we use JavaSE, we want to use JavaSE for programming, so we need to download the Java Development Environment. What is the Java Development Environment? JDK ).

First, go to Oracle (SUN has been acquired by Oracle, and Java is owned by Oracle. Of course, the MySQL database acquired by SUN also belongs to Oracle, but Oracle itself is also a database, isn't it interesting ?) Official Website: http://www.oracle.com, web pages all English do not understand it? Find Country in the upper right corner, click, select Asia Pacific, and then select China:

After that, did Oracle's official website become Chinese? Next we pull the webpage to the bottom, find and click Java:

Next, select Java for developers:

(Java for developers is JDK, and Java for consumers is JRE)

Next we will go to a full English interface again. Remember, this time cannot be changed to Chinese (curious children can try it). Then drop down and click JavaSE:

Click the DOWNLOAD button:

(Note: either of the two buttons)

Next, select the Accept License Agreement radio button, and then download the corresponding JDK based on your system version:

(Note: x86 is a 32-bit computer and x64 is a 64-bit computer)

Then the JDK installation package will be downloaded!