GetRuntime can NOT exec very simple C executable

Question

Dear all,
I compiled the following very simple C program as echo.exe in windows, now I want to use
Process process = Runtime.getRuntime().exec("echo");
to output all results from echo.exe to a JTextArea.
So I created an
inputStream = new BufferedInputStream(process.getInputStream());
and then use a thread to detect any outputs from the thread:
// inside run
while (inputStream.available()==0) {
     Thread.currentThread().sleep(100);
byte[] bytes = new byte[inputStream.available()];
inputStream.read(bytes);
/* output is a JTextArea */
output.setText(new String(bytes));
Now the problem is: it even can not print out "Prompt>", until I type "quit" to exit the program, and then print out everything save from the start.
I tested again and again by modifing the C program and noticed that the problem here is gets( line ) - seems it blocks for ever -> if I do not use this line, everything is ok. I do not know why it even does not execute printf("\nPrompt> "); going to gets(line); ?
Anything wrong here? Any suggestions?
Note: Just ignore any inputs from user now, I only needs to display "Prompt>" in JTextArea, since this is my major problem.
Many thanks!
/* echo.c*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main()
  char line[1024];
  while(1) {
    printf("\nPrompt> " ) ;
    gets( line ) ;
    if(strcmp(line,"quit") == 0) {
      break;
    else {
     printf("%s", line);
  return 0;
}

Answer 1

I haven't tried this but it should work. The output stream
should be obtained if you want to break out of the gets() statement.
when you write to the stream always include the '\n' character.
Process process = Runtime.getRuntime().exec("echo");
inputStream = new BufferedInputStream(process.getInputStream());
// inside run
String str = inputStream.readLine();
output.setText(str);
PrintWriter out = new PrintWriter(process.getOutputStream());        
out.println("quit\n");  
out.flush();
out.close();
out = null;
/* echo.c*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main()
  char line[1024]; 
  while(1)
    printf("Prompt>\n" );   
    gets( line ) ;   
    if(strcmp(line,"quit") == 0)
      break;   
    else
      printf("%s", line);   
  return 0;