Small series will be updated in the coming days to share some aspects of IT technology, as well as some of their own feelings and experiences, I hope you can gain something in me, something to grow, then we start with java.
We want to learn something and to learn it, so we need to figure out what we are going to learn what it is? How it came? Why study it? How to learn it? Only in this way can we know the meaning of learning, in order to choose the right direction, can easily learn it in the right direction.
We start to understand the history of development in the java:
It is a java programming language, what language? Language is communication, as we Mandarin, English ...., these are the communication language, programming language among our people it is only language of communication between us and the computer, we put what we want computer doing things to convey to the computer through a programming language, and then let the computer to complete our needs. There are many programming languages, the distinction between them is similar to the difference between Mandarin and English, like which includes the C language, Python language, java language, C # language, computer language is the result of generations of development, it evolved into this today kind of way closer and closer to the language of human thought. There are three stages:
- The first-generation languages: machine language (code consists of 1s and 0s, very tedious)
- The second generation language: assembly language (also known as symbolic language)
- Third-generation languages: high-level language
- Process-oriented (such as C)
- Object-oriented (e.g., C ++, java, C #, python)
- Fourth-generation languages: SQL, represented by
- Generally considered 4GL has easy to learn, a good user interface, a high degree of non-procedural, problem-oriented, just tell the computer "what", but
does not have to inform the computer "how to do"
- Generally considered 4GL has easy to learn, a good user interface, a high degree of non-procedural, problem-oriented, just tell the computer "what", but
Version Description January 1991 established the Green Sun's project team, specializing in smart appliances embedded control system in February 1991 to abandon C ++, open version described in January 1991 established the Green Sun's project team, specializing in embedded control system intelligent home appliances February 1991 to abandon C ++, to develop new language named "Oak" 1991 Nian 06 Yue JamesGosling developed the Oak interpreter January 1992 Green completed the Green OS, Oak language, class libraries developed in November 1992 Green plan transformed into "FirstPerson", a wholly-owned parent company of Sun's February 1993 order to get Time Warner's interactive television set-top box system, so the development of the center of gravity from the home consumer electronics products to the relevant platform TV set-top box. 1994 June FirstPerson company goes bankrupt, employees are merged into Sun's. Liveoak program started, the goal is to set up the Java language using the Oak and HotJava. 1996 January 1997 February JDK1.0 release J2SE1.1 released in December 1998 J2SE1.2 released three versions of Java released in June 1999: J2SE, J2EE, J2ME May 2000 J2SE1.3 released in 2001 September J2EE1.3 released in February 2002 J2SE1.4 released in September 2004 J2SE1.5 release, will be renamed JavaSE5.0 J2SE1.5 2005 June JavaSE6.0 release, J2EE renamed JavaEE, J2SE renamed JavaSE, J2ME renamed JavaME December 2006 JRE6.0 released in December 2006 JavaSE6 released in 2009 12JavaEE, J2SE renamed JavaSE, J2ME renamed JavaME December 2006 JRE6. 0 released in December 2006 JavaSE6 released in December 2009 JavaEE6 Published April 2009 Oracle acquired Sun 2011 on 07 Yue JavaSE7 released in March 2014 JavaSE8 release a new language, named "Oak" 1991 Year 06 Yue JamesGosling developed Oak, interpreter January 1992 Green Green completed operating system, Oak languages, libraries and other development plans in November 1992 Green transformed into "FirstPerson", a wholly-owned Sun's parent company in February 1993 to get Time Warner's TV set-top boxes orders interactive system, so the development of the center of gravity from the home consumer electronics products to the relevant platform TV set-top box. 1994 June FirstPerson company goes bankrupt, employees are merged into Sun's. Liveoak program started, the goal is to use the Oak language design an operating system. 1994 July First Java language Web browser WebRunner (later renamed HotJava), Oak changed its name to count out an operating system. 1994 July First Java language Web browser WebRunner (later renamed HotJava), Oak changed its name to count out an operating system. 1994 July First Java language Web browser WebRunner (later renamed HotJava), Oak changed its name to count out an operating system. 1994 July First Java language Web browser WebRunner (later renamed HotJava), Oak changed its name to count out an operating system. 1994 July First Java language Web browser WebRunner (later renamed HotJava), Oak was renamed Java. October 1994 written VanHo ff Java compiler for the Java language in March 1995 SunWorld Assembly, Sun has officially introduced Java and HotJava. 1996 January 1997 February JDK1.0 release J2SE1.1 released in December 1998 J2SE1. 2 release three versions of Java released in June 1999: J2SE, J2EE, J2ME, 2000 May 09, 2001 J2SE1.3 released J2EE1.3 released three versions of Java released in February 2002: J2SE, J2EE, J2ME J2SE1.4 released in September 2004 J2SE1.5 release, will be renamed JavaSE5.0 J2SE1.5 2005 June JavaSE6.0 release, J2EE renamed JavaEE, J2SE renamed JavaSE, J2ME renamed JavaME December 2006 JRE6. 0 released in December 2006 JavaSE6 released in December 2009 JavaEE6 published April 2009 Oracle acquired Sun 2011 07 Yue JavaSE7 released in March 2014 JavaSE8 release. (For a more detailed history of the development, you can search on Baidu review)
java father James Gosling
our lives with a lot of software is often written out by the java, such as QQ, Taobao, Jingdong, Thunder, etc., suitable for the preparation of java Internet (electricity supplier, P2P, etc.) and the type of enterprise (ERP , CRM, BOS, OA, etc.) software.
The above java version appeared in J2SE, J2EE, J2ME presentation, they in the end what is it? what differences are there? Then I was introduced to them.
J2EE, J2SE, J2ME is Sun's Java multiple versions, as well as Windows XP Professional and Home Edition are the same.
Version difference:
the J2EE: the Java 2 Platform Enterprise Edition Enterprise Edition for enterprise applications, support for distributed deployment.
J2SE: Java 2 Platform Standard Edition Standard Edition for desktop applications, is also the basis of J2EE.
J2ME: Java 2 Platform Micro Edition for small mobile devices, is a subset of J2SE.
Scope:
J2ME for embedded development, software such as mobile phones, small game consoles, TV set-top boxes and other equipment can be used to develop J2ME.
J2EE is the enterprise development, can develop web server, enterprise management platform and other large software products.
J2SE is the standard version of JAVA language used primarily in the development of computer-side software.
java development environment to build: In order to make the program up and running we can write properly, we need to install JDK and JRE (you can go to the official website to download installation https://www.oracle.com/technetwork/index.html),JDK is the development environment, JRE is the runtime environment, this environment as if our environment for human survival, oxygen, water ... we normal people can survive it, for java, the need for such an environment, it can achieve its function. java language also has a cross-platform, which is a java language compared with other big feature is also a little, what is the cross-platform? Cross-platform java is only required once, you can allow other platforms in a compiler platform, that can be achieved once, run everywhere.
Next Xiaobian share with small series that a good number of development techniques, summarized six words is: knock, look, more exchanges, 28 principles, raise interest, chasing efficiency. Mainly referring to the next two principles, see the name to know other meaning, it will not go, our social life is also subject to the 28 principles, that is, 20% of people share 80% of the wealth, 80% of people share 20 percent of the wealth, java learning what we have to abide by 28 principles, with 80% of the effort to seize 20% of the focus, with 20% of non-priority effort to learn, it will not only learn it will not be tired, but very efficient, learn very well.
BB so much, we come to the question, get some dry goods, we start with the foundation began to speak.
First, the basic unit of the computer:
1 and 0 is the basic unit of computer storage binary, including the now you see on the computer everything is composed of two numbers 1 and 0, and a 1 and 0 binary computer store the basic unit, including the now you see on the computer everything is composed of two numbers 1 and 0, and a come.
Bit (bit) bytes (Byte)
kilobytes (KB) megabytes (MB)
Gigabyte (GB) terabytes (TB)
conversion formula: 1B = 8 bit
1KB = 1024B
1MB = 1024KB
1GB = 1024MB
1TB = 1024GB
Second, common DOS commands
In the initial learning stage, after preparation of the source file needs to be compiled to operate, but in the Windows operating system to compile and run all need to understand the common DOS commands, so let's learn about common DOS commands (DOS commands is knowledge of the Windows operating system included) . DOS command is a command used in DOS console by pop-DOS console is: win + R, then the output cmd.
There are many DOS commands, we do not need to learn all the DOS command, we just need to learn to use Java in common DOS commands, as follows:
clear the screen: cls
when DOS console content too much, use the clear screen command, equivalent to "effaceurs";
for example: C: \> cls, and press Enter.
Switching letter::
By default, we are in the C disk, if you want to go to other letter can use this command;
for example: C: \> E:, and then press the Enter key to the E site;
for example: the first plate character, after the path; or first path, the drive letter.
Enter the specified directory: cd
when we want to enter a directory can use this command;
for example: D: \> cd dylan, thus entering the D: \ dylan directory, of course, you need to ensure that this directory exists;
for example: D : \> cd dylan \ java, so entered the D: \ dylan \ java directory.
Return to the parent directory: cd ..
when you need to return to the parent directory can use this command;
For example: D: \ dylan \ java> cd .., and then press ENTER, returns to D: \ directory under dylan.
Back letter root: cd \
When it is desired to return to the root directory of the current letter can use this command;
example: D: \ dylan \ java> cd \, and then press ENTER, so that it returns to the D: / a directory .
Create a folder: mkdir
example: mkdir test.
You can use this command when you need to view the current dir all files and subdirectories under the directory information: Displays the current information in the files and subdirectories in the directory.
History command: ↑ ↓
keyboard arrow keys can view the history command.
Automatically filled: tab
can use the tab key to pad some of the file names longer.
Run the application: full name of the program parameters
when you need to run an application can use this command;
for example, when you want to run the Notepad program: D: \> C: \ windows \ notepad.exe, this will open the Notepad program, this is not unlike the
C: \ windows directory under the same program, double-click the icon of the effect, because the program supports a double-click;
you can also omit ".exe" suffix, for example: D: \> C: \ windows \ notepad, effects above.
Exit: exit
You can enter exit to exit, you can also direct the top right mouse X.
Third, the programmers write the first code HelloWorld, expressed programmers say hello to the world.
HelloWorld.java
the HelloWorld class {public
public static void main (String [] args) {
System.out.println ( "the Hello World!");
}
}
Note that when you write source code must pay attention to the case. All in all, exactly the same as the first on the right, more about this later. Here we parsing the source code, the source code of the HelloWorld case divided into a total of three parts, namely: class, the main method, and an output statement.
Class
class is the outermost part, wherein the public class must write command, the HelloWorld class name is required to be the same as the name of the source file. Because our source file name HelloWorld.java, it must be the class name HelloWorld. Content class has a pair of braces, like this store in curly braces. You may ask what is the class, my answer is to not worry about what is like, now you need to write down the following code, namely grammar class definition.
the HelloWorld class {public
}
main method
of the main class is the content, the primary method of braces into class. Now we need to know more, just put the contents of the main methods to back down. The method also has a pair of main braces, used to store the content of the main process.
Output statements
output the contents of the statement is the main method, the output of statements need to put braces main method. Output statement also needs to back down. Finally, a pair of output statement parentheses, a word with the double quotes in parentheses: Hello World !. The program runs it will be output. After a pair of parentheses there is a word in double quotation marks in parentheses: Hello World !. The program runs it will be output. Here our source code had been prepared, and would also like to remind you once again to pay attention to the case when writing source code. File names and file contents should pay attention to the case.
Well, here today, and today mainly on java of an understanding, I hope you brought the harvest, followed by more of the world's best dry! ! !