USB Detection

[Isaac Hewitt]

I am running a background thread which, every 3 seconds, should detect whether a USB device has been inserted into the computer, and then changes the ViewPort view of the ScrollPane containg JTree to reflect the new drive. This end of it works perfectly, but the trouble is when a user removes the USB device and the program needs to detect this change.

public class DriveDetecter extends Thread {
      private List<java.io.File>driveList;
      private MyProgram p;
     
     
    public DriveDetecter(MyProgram p) {
        this.p= p;
        
        this.init();
    }

    private void init() {
        this.setPriority(Thread.MIN_PRIORITY);
        this.driveList = Utilities.getReadableDrives();
     
        this.pleaseWait = false;
        this.OK = true;
    }

    private boolean driveDetected() {
        List<java.io.File>list = Arrays.asList(Utilities.readableRootDrives());
        for(java.io.File f : list) {
           if(!this.driveList.contains(f)) {
              this.driveList.add(f);
                return true;
           }
       }
            return false;
    }



    @Override
    public void run() {

        while(true) {
            
          try {
             Thread.sleep(3000);
           
             if(this.driveDetected()) {
                 this.p.refreshUserFileTree();
             } 
      
           } catch(Exception e) {}
          
         
          
          }
       }

    public static List<java.io.File>getReadableDrives() {
        
        List<java.io.File>rootVector = new ArrayList<>();  ///// WAS A VECTOR ///////
        java.io.File[] rootArray = java.io.File.listRoots();
        
        java.io.File f = null;
      
        for(int j = 0; j < rootArray.length; j++) {
           f = rootArray[j];
               if(f.canRead()) {
                  rootVector.add(f);
            }
        }
        rootArray = null;
        return rootVector;
    }

[Isaac Hewitt]

I forgot mention the 2 boolean class variables are no longered used, so please ignore them in your analysis of this snippet. I am using NetBeans 7 with Java 7 update 1, which performs superbly.

[Prabakar Kalivaradan]

Can you use HashMap<String,File> to maintain a list of drives available? Where String key is the drive letter and File is the corresponding drive. This will help cross checking with drives anytime later. In your thread, you can cross check the entire map you are maintaining whenever the drives count is lesser than previous attempt; basically you need to maintain drives count as well;

something like,

if(driveCount < previousCount) // a drive gone missing
  //find the missing drive
else if(driveCount > previousCount)
  //new drive got added
else
  //no change in no.of drives(but one drive could've replaced another)

You can also use HashSet because system file drives are unique set of items.