PMD rule DataflowAnomalyAnalysis oddness.

Question

I have the following JUnit test:

@Test
public void testRunLocalhost() throws IOException, InterruptedException {
    // Start an AnnouncerThread
    final AnnouncerThread announcer = new AnnouncerThread();
    announcer.start();

    // Create the socket and listen on the right port.
    final DatagramSocket socket = new DatagramSocket();
    assert(socket != null);

    // Create a packet to send.
    final DatagramPacket packet = new DatagramPacket(new byte[0], 0, InetAddress.getByName(AnnouncerThread.GROUP), AnnouncerThread.PORT);
    assert(packet != null);

    // Send the packet.
    socket.send(packet);

    // Listen for the IP from the server.
    final DatagramPacket receivedPacket = new DatagramPacket(new byte[256], 256);
    socket.setSoTimeout(2000); // Only wait 2 seconds.
    socket.receive(receivedPacket);
    socket.close();

    // Get localhost's address.
    final InetAddress localhost = InetAddress.getLocalHost();
    assert(localhost != null);

    // Compare the receive IP to the localhost IP.
    final String receivedIP = new String(receivedPacket.getData());
    if (!receivedIP.startsWith(localhost.getHostAddress())) {
     fail("Received IP: '" + receivedIP + "' not the same as localhost: '" + localhost.getHostAddress() + "'");
    }

    announcer.shutdown();
    announcer.join();
}

And PMD gives the following violations:

Found 'UR'-anomaly for variable 'socket' (lines '36'-'36').
Found 'UR'-anomaly for variable 'localhost' (lines '36'-'36').
Found 'UR'-anomaly for variable 'packet' (lines '36'-'36').

Line 36 in my file is the line the method is defined:

public void testRunLocalhost() throws IOException, InterruptedException {

I don't understand what the violations are saying. Where should I defining those three variables? Why wasn't the AnnouncerThread in the violations? It's declared the same way I've tried re-ordering the declarations to no avail.

Answer 1

That looks rather strange. Interestingly, it occurs for all three variables that are defined for objects allocated via 'new', which you then check for nullness. I would expect the result of 'new' to always be valid/not-null - otherwise an OutOfMemoryException should be thrown. Is that the issue, I wonder ?

Answer 2

It does appear to have something to do with the assert calls you're making right after allocating those three final variables.

The PMD docs (http://pmd.sourceforge.net/rules/controversial.html#DataflowAnomalyAnalysis) say:

UR - Anomaly: There is a reference to a variable that was not defined before