What do the experts use to program?

The first java program - edit using Notepad

---

---

Friends who have successfully built the java environment in the previous article can write their own java on their own computers Programmed yo~ If you haven’t set up environment variables yet, please move to the previous essay to complete the set up.

Connection address:

Now we can edit our first java applet by using Notepad.

The first step is to use Notepad to edit the program code

What is written in Notepad is the java source code file, and the code inside is the java code we usually study. The suffix of the generated file is a .java file. The .java file cannot be directly executed and needs to be processed through subsequent compilation to become an executable program.

Second step, use the javac command to compile the source code file

Javac is its own compiler. Its function is to compile the source code file. In layman’s terms, compilation means to compile the source code file. The process of parsing code files into files that can be read by computers (computers cannot directly read high-level languages ​​​​such as Java).

The third step is to compile it into a bytecode file

Through the above steps, the source file has been successfully compiled into a bytecode file, which ends with .class. Bytecode files have nothing to do with the operating system. The final compiled bytecode files are the same whether under Windows or Linux. (Note: Java’s cross-platform performance is fundamentally due to the existence of bytecode files)

The fourth step is to use the interpreter to run the file

The last step is to use the java command according to different platform systems Start the interpreter to execute the bytecode file, and eventually we will see the results on the screen.

The above steps can be clearly represented by the following picture:

---

Next, let’s practice it in practice (hehe , exaggerated):

First, look at the first step. I created a new text file on the desktop and renamed it myProgram.java. (Note that the file name must be the same as the type, otherwise an error will be reported!)

Edit the file content as follows, a very classic hello world program:

public class myProgram
{public static void main (String[] args){
System.out.println("Hello World！！");
}
}

　

　

After saving, there will be a source file of myProgram.java on the desktop.

# Then we will complete the second step and use the Javac command to compile the source file.

Open cmd, and then switch to the root directory of the source code (I built it on the desktop, so my root directory is C:\Users\acer\Desktop)

　

After entering the root directory, use the javac command to compile the myProgram.java file

After the compilation is completed, no error message will appear, and it will be generated in the root directory myProgram.class file

　

Note: If you directly execute the myProgram.java file with the java command, an error will be reported

##　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　# Finally, we use the java command to execute the myProgram.class file                

　

Note: If you add the .class suffix at the end, an error will be reported that the main class cannot be found or cannot be loaded. Here we must remember that the java command cannot be followed by a file suffix! ! Remember! !

# Note: The case cannot be mistaken (because Java is case-sensitive).

Because javac is the operating system compilation source file; java is run by JVM, and what is run is a class~not a file, so .class cannot be used after it, and the class name is used directly. 　

Supplement to the above example: If there are spaces in the file name or path, an error will be reported if you directly use the file name or path, and the spaces cannot be recognized. For example: Are you sure.java only in cmd It can be recognized as sure.java. This is because Java class names do not allow spaces, so this way of naming files is wrong. The problem of spaces in the path can be solved by adding "" double quotes to the path, as shown in the following figure:

When the file name has spaces (error, spaces are not allowed in class names)

      

The path has spaces (can be solved by double quotes)

## Okay, such a simple java program is used Notepad can be used to edit and run directly. I heard that experts all use Notepad to program directly. Of course, this article is just an understanding of Notepad programming. Newbies like me can just use eclipse and other compilers. Device.

The above is the detailed content of What do the experts use to program?. For more information, please follow other related articles on the PHP Chinese website!