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This article mainly introduces "how to write java screen cleaning code". In daily operation, I believe many people have doubts about how to write java screen cleaning code. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful to answer the doubts of "how to write java screen cleaning code". Next, please follow the editor to study!

Why can't java clear the screen directly?

In fact, not only java, but also python,c language, most languages have no way to directly clear the screen, want to clear the screen, you need to call the system function (actually a command). Because the screen cleaning function needs to go deep into the system kernel to operate, and ordinary java programs have no way to enter the kernel (in fact, it is not without, after learning the relevant lessons of the operating system, you will know how to get java programs into the kernel state). To put it simply, the operating system is divided into user mode and kernel mode, and the function of screen cleaning can only be realized in kernel mode, while java program is only in user mode, so it can not clear the screen, but can only clear the screen through commands provided by the kernel.

In fact, the knowledge of user state and kernel state does not need to be mastered too much for beginner java programmers, just need to know that java does not have the function of cleaning the screen directly.

How to clear the screen of java

Java actually uses the same method as python to clear the screen, and java also provides packages that allow java to use the cmd command. Next let's take a look at how java invokes the cmd command.

Java invokes cmd command instance

The following is an example of java calling cmd's ping command, and the specific code description has been written in the comments.

Import java.io.BufferedReader;import java.io.InputStreamReader;public class cmd {public static void main (String [] args) {String command = "ping www.yisu.com"; / / the string of commands to be entered try {/ / the process of using the command may fail and the exception Process process = Runtime.getRuntime () .exec (command) needs to be caught / / using process, you can execute the command process.waitFor (); / / causes the current thread to wait, if necessary, until the process represented by the Process object has terminated. / / this method returns immediately if the child process has been terminated. / / if the child process is not terminated, the calling thread will be blocked until the child process is exited. / / according to convention, 0 means normal termination of BufferedReader out = new BufferedReader (new InputStreamReader (process.getInputStream (), "GBK")); / / get the output stream of the command String outline = null; while ((outline = out.readLine ())! = null) {System.out.println (outline) } / / the output stream of the output command System.out.println ("status value is:" + process.exitValue ()); / / the return value of the output command (execution status, 0 is successful)} catch (Exception e) {e.printStackTrace ();}

You can learn from the above code that you can execute the cmd command using process's Runtime.getRuntime (). Exec (command), but if you want to see the result returned by the cmd command, you need to use process.getInputStream () to get the output stream of cmd.

Advanced version of process

The above version of process is a relatively simple way to execute a command prompt, but there is an error when this method is used to clear the screen. However, his advanced version, processbuilder, does not have such a problem. Next, we use processbuilder to implement the screen cleaning code:

Public class cmd {public static void main (String [] args) {System.out.println ("print some useless content"); System.out.println ("print some useless content"); System.out.println ("print some useless content"); System.out.println ("print some useless content") System.out.println ("print some useless content"); try {/ / the process of using the command may fail and you need to catch the exception / / Process process = Runtime.getRuntime () .exec ("cls") New ProcessBuilder ("cmd", "/ c", "cls") / / associates the output pipeline of the ProcessBuilder object with the process of Java The return value of this function is also a / / ProcessBuilder .SecretitIO () / / start to execute the command in ProcessBuilder. Start () / wait for the screen cleaning command in ProcessBuilder to finish / / if you don't wait, the output after the screen cleaning code will be cleared. Waitfor () / / clear the screen command} catch (Exception e) {e.printStackTrace ();} System.out.println ("there is no useless content now, let's talk about something important"); System.out.println ("learn programming, which is better? Shine on the Internet ";}} at this point, the study on" how to write the java screen cleaning code "is over, hoping to solve everyone's doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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