Question

Is there a way to dynamically change output in Java? For instance, in a terminal window if I have:

System.out.print("H")

and then I have:

System.out.print("I")

The output will be:

HI

Is there a way to assign a position to outputs that allows you to replace characters dynamically? For instance (and I know this would not output what I want, I merely want to demonstrate my thinking) this:

 System.out.print("H")
 Thread.sleep("1")
 System.out.print("I")

And it would first print out

H

and then after a second, replace the H with an I?

I’m sure this sounds stupid, I am just interested in dynamically changing content without GUIs. Can someone point me in the direction for this technique? Thank you very much in advance.

Answer 1

You might want to take a look at

System.out.printf

Look at the example shown here: http://masterex.github.com/archive/2011/10/23/java-cli-progress-bar.html

edit:

printf displays formatted strings, which means you can adapt that format and change it for your needs.

for example you could do something like:

String[] planets = {"Mars", "Earth", "Jupiter"};        
String format = "\r%s says Hello";

for(String planet : planets) {
    System.out.printf(format, planet);
try { 
        Thread.sleep(1000); 
    }catch(Exception e) { 
        //... oh dear
    }
}

Using the formatted string syntax found here: http://docs.oracle.com/javase/6/docs/api/java/util/Formatter.html#syntax

As the comment says this solution is only limited to a singular line however dependent on your needs this might be enough.

If you require a solution for the whole screen then a possible solution would be (although quite dirty) would be to hook the operating system using JNA and get a handle on the console window, find its height and then loop println() to “clear” the window then redraw your output.

If you would like to read more then I can answer more questions or here is a link: https://github.com/twall/jna