Java IO.pdf - Nguyen Dang Binh

javax.comm.CommPortIdentifier@be4c9581
Java I/O
This shows you that my system has four ports, though it doesn't tell you what those ports are.
Of course, the output will vary depending on how many serial and parallel ports your system
possesses, and those first few lines are liable to disappear in the release version of the Comm
API. Clearly, a better toString() method is needed. (CommPortIdentifier merely inherits
java.lang.Object's toString() method.) You'll see how to work around this in the next
section.
You can also get a CommPortIdentifier by using the static method getPortIdentifier()
to request a port identifier, either by name or by the actual port object. The latter assumes that
you already have a reference to the relevant port, which usually isn't the case. The former
allows you to choose from Windows standard names like "COM1" and "LPT2" or Unix
names like "Serial A" and "Serial B." The exact format of a name is highly platform- and
implementation-dependent. If you ask for a port that doesn't exist, a NoSuchPortException is
thrown. Example 17.2 looks for serial and parallel ports by starting with COM1 and LPT1 and
counting up until one is missing. Be warned that this code is highly platform-dependent and
probably won't work on Unix or the Mac.
Example 17.2. NamedPortLister
import javax.comm.*;
public class NamedPortLister {
}
public static void main(String[] args) {
}
// List serial (COM) ports.
try {
int portNumber = 1;
while (true) {
CommPortIdentifier.getPortIdentifier("COM" + portNumber);
System.out.println("COM" + portNumber);
portNumber++;
}
}
catch (NoSuchPortException e) {
// Break out of loop.
}
// List parallel (LPT) ports.
try {
int portNumber = 1;
while (true) {
CommPortIdentifier.getPortIdentifier("LPT" + portNumber);
System.out.println("LPT" + portNumber);
portNumber++;
}
}
catch (NoSuchPortException e) {
// Break out of loop.
}
Once again, here's the output from a stock Wintel box:
431