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"null" in Java drawImage()

I mean the drawImage() method is not working for me. People say to do like
g.drawImage(image, 0, 0, null);
But eclipse actually deny it. It said:
The method drawImage(Image, int, int, ImageObserver) in the type Graphics is not applicable for the arguments (Image, int, int, null)
This actually make my really confused, I have read some answers from others, which they always say to put it to null.
I tried to run it, and it give me this:
Exception in thread "AWT-EventQueue-0" java.lang.Error: Unresolved compilation problem:
The method drawImage(Image, int, int, ImageObserver) in the type Graphics is not applicable for the arguments (Image, int, int, null)
at me.danielshe.graphics.DrawComponent.paintComponent(DrawComponent.java:29)
at javax.swing.JComponent.paint(Unknown Source)
at javax.swing.JComponent.paintChildren(Unknown Source)
at javax.swing.JComponent.paint(Unknown Source)
at javax.swing.JComponent.paintToOffscreen(Unknown Source)
at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(Unknown Source)
at javax.swing.RepaintManager$PaintManager.paint(Unknown Source)
at javax.swing.RepaintManager.paint(Unknown Source)
at javax.swing.JComponent._paintImmediately(Unknown Source)
at javax.swing.JComponent.paintImmediately(Unknown Source)
at javax.swing.RepaintManager$4.run(Unknown Source)
at javax.swing.RepaintManager$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.prePaintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.access$1200(Unknown Source)
at javax.swing.RepaintManager$ProcessingRunnable.run(Unknown Source)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)
Can anyone help me, or is that a way to put something instead of "null"? I have tried to put "this" and even implementing the ImageObserver. But neither of them works.
Thanks.

You need an object that implements the ImageObserver interface. Normally
this is would be the component associated with the graphics object.

Using null as an ImageObserver it's not wrong. Is equivalent to this:
ImageObserver obs = null;
drawImage( img, x , y , obs );
Null can be used anywhere you would use a reference (Object). The problem arises when you need to use this reference/object, you will get a runtime exception as the object would be empty. In your example as long as your image is fully loaded when you call drawImage(), you won't have a problem, therefore you should only use null on drawImage() if you know for sure that your image is fully loaded. Now I haven't had this problem with the compiler, but I don't use eclipse, just a text editor and the command line. Try compiling with the command line or use the two lines of code from above on eclipse.
"this" will only work if the class where you are using drawImage implements the ImageObserver interface or if it extends a class that implements it, like a Jcomponent for example.

Java: "unknown source" error with unfolding maps package

BACKGROUND
I'm trying to build a map of earthquake events with data parsed from an RSS feed using the "Unfolding maps" library in Java (this is part of the Coursera course on OOP with Java). In theory, the data from the feed gets parsed into properties of the earthquake (location, magnitude, ...) which then form the basis for these marker objects that get displayed on a map. The libraries that are used are "Processing" and the "Unfolding Maps" library.
PROBLEM
Theres an "Unknown Source" error in the part, where I want to set the color property of the earthquake marker, depending on the magnitude of the event (ie. magnitude > 3 is "yellow").
Here's the error message:
Exception in thread "Animation Thread" java.lang.NullPointerException
at de.fhpotsdam.unfolding.marker.AbstractMarker.getProperty(Unknown Source)
at module3.EarthquakeCityMap.setup(EarthquakeCityMap.java:101)
at processing.core.PApplet.handleDraw(PApplet.java:2365)
at processing.opengl.PJOGL$PGLListener.display(PJOGL.java:873)
at jogamp.opengl.GLDrawableHelper.displayImpl(GLDrawableHelper.java:690)
at jogamp.opengl.GLDrawableHelper.display(GLDrawableHelper.java:672)
at javax.media.opengl.awt.GLCanvas$10.run(GLCanvas.java:1383)
at jogamp.opengl.GLDrawableHelper.invokeGLImpl(GLDrawableHelper.java:1277)
at jogamp.opengl.GLDrawableHelper.invokeGL(GLDrawableHelper.java:1131)
at javax.media.opengl.awt.GLCanvas$11.run(GLCanvas.java:1394)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)
And here is the code
for (Marker marker:markers) {
if ((int) (marker.getProperty("magnitude")) > 3) {
System.out.println("trying to set the colour to yellow");
//marker.setColor(yellow);
}
}
The line with "setColor(yellow)" is commented out, as it seems that this is a problem of its own (may or may not have to do with it).
Anybody have an idea where this may come from and what I could read up on to better understand the problem? I'm pretty new to programming so any advice on how to learn the process of tracing errors / finding out the cause of a problem would be fantastic.

Call to Cipher.getInstance makes an ftp call

My application makes call to Cipher.getInstance so it can decrypt passwords.
In certain environments this is creating a problem because the Cipher.getInstance method ends up trying to make an FTP call which is hanging.
Does anyone know how to avoid this FTP call or prevent it hanging?
Here is the stacktrace.
java.net.PlainSocketImpl.socketConnect(Native Method)
java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:370)
java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:231)
java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:213)
java.net.Socket.connect(Socket.java:643)
java.net.Socket.connect(Socket.java:590)
sun.net.ftp.impl.FtpClient.doConnect(FtpClient.java:971)
sun.net.ftp.impl.FtpClient.tryConnect(FtpClient.java:931)
sun.net.ftp.impl.FtpClient.connect(FtpClient.java:1026)
sun.net.ftp.impl.FtpClient.connect(FtpClient.java:1012)
sun.net.www.protocol.ftp.FtpURLConnection.connect(FtpURLConnection.java:307)
sun.net.www.protocol.ftp.FtpURLConnection.getInputStream(FtpURLConnection.java:406)
sun.net.www.protocol.jar.URLJarFile.retrieve(URLJarFile.java:227)
sun.net.www.protocol.jar.URLJarFile.getJarFile(URLJarFile.java:84)
sun.net.www.protocol.jar.JarFileFactory.get(JarFileFactory.java:128)
sun.net.www.protocol.jar.JarURLConnection.connect(JarURLConnection.java:136)
sun.net.www.protocol.jar.JarURLConnection.getJarFile(JarURLConnection.java:103)
javax.crypto.a$0.run(Unknown Source)
java.security.AccessController.doPrivileged(AccessController.java:420)
javax.crypto.a.a(Unknown Source)
javax.crypto.a.a(Unknown Source)
javax.crypto.a.a(Unknown Source)
javax.crypto.b.a(Unknown Source)
javax.crypto.d.a(Unknown Source)
javax.crypto.d.a(Unknown Source)
javax.crypto.Cipher.c(Unknown Source)
javax.crypto.Cipher.b(Unknown Source)
javax.crypto.Cipher.getInstance(Unknown Source)
javax.crypto.Cipher.getInstance(Unknown Source)

App Engine / Quercus datastore prepare query error

I'm trying to replicate the java guestbook example on Quercus on AppEngine and I'm getting an error having to do with preparing the query:
$greetings = $datastore->prepare($query)->asIterable();
I'm not a java developer so I can't make sense of the error trace. How can I get the greeting items without triggering this error?
Here is the entire error page:
HTTP ERROR 500
Problem accessing /index.php. Reason:
INTERNAL_SERVER_ERROR
Caused by:
java.lang.NullPointerException at
com.google.appengine.api.datastore.dev.LocalDatastoreService.next(LocalDatastoreService.java:1089)
at sun.reflect.GeneratedMethodAccessor8.invoke(Unknown Source) at
sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at
java.lang.reflect.Method.invoke(Unknown Source) at
com.google.appengine.tools.development.ApiProxyLocalImpl$AsyncApiCall.callInternal(ApiProxyLocalImpl.java:498)
at
com.google.appengine.tools.development.ApiProxyLocalImpl$AsyncApiCall.call(ApiProxyLocalImpl.java:452)
at
com.google.appengine.tools.development.ApiProxyLocalImpl$AsyncApiCall.call(ApiProxyLocalImpl.java:430)
at java.util.concurrent.Executors$PrivilegedCallable$1.run(Unknown
Source) at java.security.AccessController.doPrivileged(Native Method)
at java.util.concurrent.Executors$PrivilegedCallable.call(Unknown
Source) at java.util.concurrent.FutureTask$Sync.innerRun(Unknown
Source) at java.util.concurrent.FutureTask.run(Unknown Source) at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

If it's a null pointer exception then you are trying to access a method or property of a null object
First you need to check if $datastore is null, then if the return of the query is not null. Also you need to check if that error is on that particular line of code (maybe it fails somewhere else)
You can access the database at this link /_ah/admin. Maybe there is a corrupt entity in there

What's the difference between http://localhost:8000/ and http://127.0.0.1:8000/ for Java Applets

I have a question/problem related to Java Applet security...
I use the Applet that has to take files from server (ASP.NET) and represent the information from it. Applet take files using the code:
URL u = new URL(getCodeBase(), filename);
BufferedReader d = new BufferedReader(new InputStreamReader(u.openStream()));
This code appears in two places:
Init() method
Some another method Test() that called manually from JavaScript
So, when I try to load the page with Applet using the URL http://127.0.0.1:8000/Test.aspx, everything works fine and I can read file content from both methods. But if I change the URL on http://localhost:8000/, only the first method works properly and I can get files content and for the second one I get the next error message in JavaConsole:
java.security.AccessControlException: access denied (java.net.SocketPermission 127.0.0.1:8000 connect,resolve)
What it the difference in this case? Why 'localhost' is impossible in this case? Is there any way how to grant access to 'localhost' the same as 127.0.0.1?
here is simplest applet's example:
public class TestApplet extends Applet {
public void init()
{
System.out.println( "init...");
readDocument();
}
public void readDocument()
{
System.out.println( "read test.txt file...");
URL base = getCodeBase();
String filename = "test.txt";
try {
URL u = new URL(base, filename);
BufferedReader d = new BufferedReader(new InputStreamReader(u.openStream()));
System.out.println(d.readLine());
System.out.println("Done!");
} catch (Exception e) {
e.printStackTrace();
}
}
}
and next code used on the client side:
<applet archive="/Content/test.jar" code="test.TestApplet.class" name="testApplet" mayscript></applet>
<script language="javascript" type="text/javascript">
$(document).ready(function () {
var testApplet = document.testApplet;
testApplet.readDocument();
});
</script>
this code works perfectly when I try to use http://127.0.0.1:8000/Test.aspx
and doesn't work when I user http://localhost:8000/Test.aspx. I java console I see the next:
init...
read test.txt file...
some text...
Done!
read test.txt file...
java.security.AccessControlException: access denied (java.net.SocketPermission 127.0.0.1:8000 connect,resolve)
at java.security.AccessControlContext.checkPermission(Unknown Source)
at java.security.AccessController.checkPermission(Unknown Source)
at java.lang.SecurityManager.checkPermission(Unknown Source)
at java.lang.SecurityManager.checkConnect(Unknown Source)
at sun.plugin2.applet.Applet2SecurityManager.checkConnect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at sun.net.NetworkClient.doConnect(Unknown Source)
at sun.net.www.http.HttpClient.openServer(Unknown Source)
at sun.net.www.http.HttpClient.openServer(Unknown Source)
at sun.net.www.http.HttpClient.<init>(Unknown Source)
at sun.net.www.http.HttpClient.New(Unknown Source)
at sun.net.www.http.HttpClient.New(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.connect(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
at java.net.URL.openStream(Unknown Source)
at test.TestApplet.readDocument(TestApplet.java:30)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at sun.plugin.javascript.JSInvoke.invoke(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at sun.plugin.javascript.JSClassLoader.invoke(Unknown Source)
at sun.plugin2.liveconnect.JavaClass$MethodInfo.invoke(Unknown Source)
at sun.plugin2.liveconnect.JavaClass$MemberBundle.invoke(Unknown Source)
at sun.plugin2.liveconnect.JavaClass.invoke0(Unknown Source)
at sun.plugin2.liveconnect.JavaClass.invoke(Unknown Source)
at sun.plugin2.main.client.LiveConnectSupport$PerAppletInfo$DefaultInvocationDelegate.invoke(Unknown Source)
at sun.plugin2.main.client.LiveConnectSupport$PerAppletInfo$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at sun.plugin2.main.client.LiveConnectSupport$PerAppletInfo.doObjectOp(Unknown Source)
at sun.plugin2.main.client.LiveConnectSupport$PerAppletInfo$LiveConnectWorker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
P.S.: Applet is signed.

The problem is the call from JavaScript. If you are using JavaScript to call your method, the permissions of the call get down to the intersection of the JavaScript bridge's permissions (i.e. nothing) and the permissions of your own code - even if your own code is signed.
To avoid this, and use the full privileges of your applet's code, put the security-relevant parts inside a AccessController.doPrivileged(...) call. (Of course, your applet should first check that this can't do anything malicious.)
I have no idea why it works if you are using the IP address directly instead of localhost, though.

localhost is an alias for 127.0.0.1 so you may have to set/fix it in your enviroment. Under Windows you have to edit the file C:\Windows\System32\drivers\etc\hosts.

localhost is typically resolved to both ::1 and 127.0.0.1 and the OS/libc is usually set up so that IPv6 is preferred in these circumstances.
Therefore, it's likely you're allowing only 127.0.0.1 and not IPv6 connections from ::1.