Java IO.pdf - Nguyen Dang Binh

Java I/O
By default, no events are fired when the serial port's state changes. If you pass true to any of
these methods, the VM will fire a serial port event when the matching state changes. Example
17.8 activates the Ring Indicator and prints a message on System.out when the modem tells
the computer the phone is ringing.
Example 17.8. PhoneListener
import javax.comm.*;
import java.util.TooManyListenersException;
public class PhoneListener implements SerialPortEventListener {
public static void main(String[] args) {
String portName = "COM1";
if (args.length > 0) portName = args[0];
PhoneListener pl = new PhoneListener();
try {
CommPortIdentifier cpi =
CommPortIdentifier.getPortIdentifier(portName);
if (cpi.getPortType() == CommPortIdentifier.PORT_SERIAL) {
SerialPort modem = (SerialPort) cpi.open("Phone Listener", 1000);
modem.notifyOnRingIndicator(true);
modem.addEventListener(pl);
}
}
catch (NoSuchPortException e) {
System.err.println("Usage: java PhoneListener port_name");
}
catch (TooManyListenersException e) {
// shouldn't happen in this example
}
catch (PortInUseException e) {System.err.println(e);}
}
}
public void serialEvent(SerialPortEvent evt) {
}
System.err.println(evt.getEventType());
if (evt.getEventType() == SerialPortEvent.RI) {
System.out.println("The phone is ringing");
}
17.5 Parallel Ports
Parallel ports are most common on PCs. Sun SparcStations from the Sparc V on also have
them. However, Macs do not have them, nor do many non-x86 workstations. Parallel ports are
sometimes called printer ports, because their original purpose was to support printers. The
names of the parallel ports—"LPT1," "LPT2," etc.—stand for "Line PrinTer," reflecting this
usage. Nowadays, parallel ports are also used for Zip drives, tape drives, and various other
devices. However, parallel ports are still largely limited by their original goal of providing
simple printing. A parallel port sends data eight bits at a time on eight wires. These bits are
sent at the same time in parallel, hence the name. The original parallel ports only allowed data
to flow one way, from the PC to the printer. The printer could only respond by sending a few
452