Clearing text from the console

[sp11k3t3ht3rd]

Okay so I'm making a program that is text-based and will print out a lot of text to the screen. I am using a batch file to run the program and I was wondering if there is any command to clear the screen in the sense that "cls" clears the batch window when creating a batch file.

[Freaky Chris]

This isn't a topic which arises much in a Java environment, however it does in the C/C++ environment. The topic of clearing text from the console is a very sore point.

The long and short of it is, you should never clear the console window.


Chris

[sp11k3t3ht3rd]

Alright. I just figured it would look nicer. Thanks for the help!

[Freaky Chris]

Your Welcome,

I Understand that principle, but trust me it's not worth it.

Think about the cmd window, when does microsoft ever clear it hehe

Chris

[helloworld922]

Well, when you ask the user to enter something like a password it'd be nice to clear the console I can't remember why Java was never implemented to allow the programmer to clear the console, but I think it had something to do with cross-platform issues.

[Freaky Chris]

Yes it does raise cross platform issues, as to do it you must target the OS for its commands to do so.
For example on windows, this is how you would go about it.

Console.h

#include <jni.h>
/* Header for class Console */
 
#ifndef _Included_Console
#define _Included_Console
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     Console
 * Method:    clr
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_Console_clr
  (JNIEnv *, jobject);
 
#ifdef __cplusplus
}
#endif
#endif

Console.c

#include <windows.h>
#include <jni.h>
 
#ifdef __cplusplus
extern "C" {
#endif
	JNIEXPORT void JNICALL Java_Console_clr(JNIEnv *, jobject){
 
       /*
       * Get Console HANDLE for control
       */
 
       HANDLE chwnd = GetStdHandle(STD_OUTPUT_HANDLE);
 
       COORD coordScreen = { 0, 0 };
       DWORD cCharsWritten;
 
 
        /*
        * Ensure text colours are stored and set
        */
       {
           WORD textColours;
           CONSOLE_SCREEN_BUFFER_INFO *consoleInfo = new CONSOLE_SCREEN_BUFFER_INFO();
           GetConsoleScreenBufferInfo(chwnd, consoleInfo);
           textColours = consoleInfo->wAttributes;
           SetConsoleTextAttribute(chwnd, textColours);
       }
 
       CONSOLE_SCREEN_BUFFER_INFO csbi;
       DWORD dwConSize;
 
 
        /*
        * If fail to get Console Dimensions, return
        */
 
       if( !GetConsoleScreenBufferInfo( chwnd, &csbi ))
          return;
       dwConSize = csbi.dwSize.X * csbi.dwSize.Y;
 
        /*
        * Return on error when filling the screen with ' '
        */
 
       if( !FillConsoleOutputCharacter( chwnd, (TCHAR) ' ',
          dwConSize, coordScreen, &cCharsWritten ))
          return;
 
       if( !GetConsoleScreenBufferInfo( chwnd, &csbi ))
          return;
 
       if( !FillConsoleOutputAttribute( chwnd, csbi.wAttributes,
          dwConSize, coordScreen, &cCharsWritten ))
          return;
 
       /*
       * Return Cursor to Origin of Console
       */
 
       SetConsoleCursorPosition( chwnd, coordScreen );
 
       return;
	}
 
#ifdef __cplusplus
}
#endif

Compile with under G++

g++ -Wall -D_JNI_IMPLEMENTATION_ -Wl,--kill-at -I"C:/Program Files/Java/jdk1.6.0_14/include" -I"C:/Program Files/Java/jdk1.6.0_14/include/win32" -shared ConsoleClear.c -o ConsoleClear.dll

Console.java

/*
 * Usage: Console.clr()
 */
 
public class Console {
 
	/*
	 * Load External DLL for clr Function
	 */
	static {
		System.loadLibrary("ConsoleClear");
	}
 
	public static native void clr();
}

Example usage

import java.util.Scanner;
 
public class Example {
 
	public static void main(String[] args) {
		System.out.print("Hello, shall I clear the screen? (y/n) :> ");
		if(new Scanner(System.in).nextLine().equalsIgnoreCase("y")){
			Console.clr();
			System.out.println("Console Cleared!");
		}else{
			System.out.println("Console not cleared!");
		}
 
	}
 
}

The reason why clearing is frowned upon is because applications running in the console can quite often me running just after other applcations have been executed, and clearing the console should not be done because it will clear the output of the previous applications data.

Chris