You need to read InputStream from the process, here is an example:

Edit I modified the code as suggested here to receive the errStream with the stdInput

ProcessBuilder builder = new ProcessBuilder("command goes here");
builder.redirectErrorStream(true);
Process process = builder.start();
InputStream is = process.getInputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(is));

String line = null;
while ((line = reader.readLine()) != null) {
   System.out.println(line);
}

For debugging purpose, you can read the input as bytes instead of using readLine just in case that the process does not terminate messages with newLine

Here are the primary differences between using System.out/.err/.in and System.console():

• System.console() returns null if your application is not run in a terminal (though you can handle this in your application)
• System.console() provides methods for reading password without echoing characters
• System.out and System.err use the default platform encoding, while the Console class output methods use the console encoding

This latter behaviour may not be immediately obvious, but code like this can demonstrate the difference:

public class ConsoleDemo {
  public static void main(String[] args) {
    String[] data = { "\u250C\u2500\u2500\u2500\u2500\u2500\u2510", 
        "\u2502Hello\u2502",
        "\u2514\u2500\u2500\u2500\u2500\u2500\u2518" };
    for (String s : data) {
      System.out.println(s);
    }
    for (String s : data) {
      System.console().writer().println(s);
    }
  }
}

On my Windows XP which has a system encoding of windows-1252 and a default console encoding of IBM850, this code will write:

???????
?Hello?
???????
┌─────┐
│Hello│
└─────┘

Note that this behaviour depends on the console encoding being set to a different encoding to the system encoding. This is the default behaviour on Windows for a bunch of historical reasons.

To be honest I find it odd in a GUI environment to accept input from the user via command line instead of some dialog (I mean you display a GUI) but you could just use a Runtime to execute a command prompt. Look here cmd using java

You can see from ls that you already compiled your program with the compiler javac. The command you used

javac hello.java

creates hello.class without sending any output to stdout, so there won't be any messages in your terminal unless there are errors - what you see is the expected behaviour. If you actually want to see some output, you can add an option: javac -verbose hello.java as mentioned by @Frisky (thanks!)

Now you can run that file hello.class with

java hello