Use Unchecked or unsafe operations: recompile with -Xlint

Question

hi all..
I'm trying to create a GUI to select the necessary port to open. I got this code from JAVA cookbook:
I'm using windows XP and JDK 1.6..
import java.io.*;
import javax.comm.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
public class PortChooser extends JDialog implements ItemListener {
HashMap map = new HashMap();
String selectedPortName;
CommPortIdentifier selectedPortIdentifier;
JComboBox serialPortsChoice;
JComboBox parallelPortsChoice;
JComboBox other;
SerialPort ttya;
JLabel choice;
protected final int PAD = 5;
public void itemStateChanged(ItemEvent e) {
selectedPortName = (String)((JComboBox)e.getSource()).getSelectedItem();
selectedPortIdentifier = (CommPortIdentifier)map.get(selectedPortName);
choice.setText(selectedPortName);
public String getSelectedName() {
return selectedPortName;
public CommPortIdentifier getSelectedIdentifier() {
return selectedPortIdentifier;
public static void main(String[] ap) {
PortChooser c = new PortChooser(null);
c.setVisible(true);// blocking wait
System.out.println("You chose " + c.getSelectedName() +" (known by " + c.getSelectedIdentifier() + ").");
System.exit(0);
public PortChooser(JFrame parent) {
super(parent, "Port Chooser", true);
makeGUI();
populate();
finishGUI();
protected void makeGUI() {
Container cp = getContentPane();
JPanel centerPanel = new JPanel();
cp.add(BorderLayout.CENTER, centerPanel);
centerPanel.setLayout(new GridLayout(0,2, PAD, PAD));
centerPanel.add(new JLabel("Serial Ports", JLabel.RIGHT));
serialPortsChoice = new JComboBox();
centerPanel.add(serialPortsChoice);
serialPortsChoice.setEnabled(false);
centerPanel.add(new JLabel("Parallel Ports", JLabel.RIGHT));
parallelPortsChoice = new JComboBox();
centerPanel.add(parallelPortsChoice);
parallelPortsChoice.setEnabled(false);
centerPanel.add(new JLabel("Unknown Ports", JLabel.RIGHT));
other = new JComboBox();
centerPanel.add(other);
other.setEnabled(false);
centerPanel.add(new JLabel("Your choice:", JLabel.RIGHT));
centerPanel.add(choice = new JLabel());
JButton okButton;
cp.add(BorderLayout.SOUTH, okButton = new JButton("OK"));
okButton.addActionListener(new ActionListener() {
     public void actionPerformed(ActionEvent e) {
          PortChooser.this.dispose();
/** Populate the ComboBoxes by asking the Java Communications API
* what ports it has. Since the initial information comes from
* a Properties file, it may not exactly reflect your hardware.
protected void populate() {
Enumeration pList = CommPortIdentifier.getPortIdentifiers();
while (pList.hasMoreElements()) {
CommPortIdentifier cpi = (CommPortIdentifier)pList.nextElement();
// System.out.println("Port " + cpi.getName());
map.put(cpi.getName(), cpi);
if (cpi.getPortType() == CommPortIdentifier.PORT_SERIAL) {
serialPortsChoice.setEnabled(true);
serialPortsChoice.addItem(cpi.getName());
else if (cpi.getPortType() == CommPortIdentifier.PORT_PARALLEL) {
parallelPortsChoice.setEnabled(true);
parallelPortsChoice.addItem(cpi.getName());
else {
other.setEnabled(true);
other.addItem(cpi.getName());
serialPortsChoice.setSelectedIndex(-1);
parallelPortsChoice.setSelectedIndex(-1);
protected void finishGUI() {
serialPortsChoice.addItemListener(this);
parallelPortsChoice.addItemListener(this);
other.addItemListener(this);
pack();
//addWindowListener(new WindowCloser(this, true));
}}When i compile this it says PortChooser.java uses unchecked or unsafe operation
recompile with -Xlint(any one know what this is?)
Is it the JDK version i'm using ? First i thought it's a security issue.As in windows is not letting me access the serial ports.
I checked with device manager.My serial ports are open. Ichanged my BIOS settings as well..
(I read inputs from parallel port.But i dont use the comm api for that)
I have installed the rxtx gnu.io package as well..
Tried import gnu.io.* instead of javax.comm.*; still the same compilatiion error!!!
Thanks in advance
goodnews:-(

Answer 1

It is basically a warning (not an error) that the compiler gives you to let you know that you are using a raw type where Java now supports generic types.
For example, in the code you use:
HashMap where you can use HashMap<String,String> to let the compiler know that you intend inserting Strings for both the key and the value. The former is considered to be unsafe because the compiler cannot control what is inserted into the HashMap while in the latter case it can ensure that only Strings are used for both keys and values.
The compiler is also letting you know that if you want to see the details of these "unsafe" operations you can use the -Xlint:unchecked option when compiling and the compiler will show you exactly which lines contain the code that is generating the warning. So to compile with this option you would use javac -Xlint:unchecked ClassToCompile.