Why got Nullpointer use getJarPath.class.getResource(".").getPath() ?

hi,
I have a question about the following program:
public class getJarPath {
public getJarPath() {
public static void main(String[] arg) {
System.out.println("java.net.URl->" + getJarPath.class.getResource(
"getJarPath.class"));
System.out.println("getPath->" + getJarPath.class.getResource(
"getJarPath.class").getPath());
System.out.println("getFile->" + getJarPath.class.getResource(
"getJarPath.class").getFile());
System.out.println("getPath with . ->"+getJarPath.class.getResource(".").getPath()); // NullPointer occured
1. compile getJarPath.java
D:\>D:\j2sdk1.4.2_04\bin\javac getJarPath.java
2. run this test program with "java getJarPath"
D:\>D:\j2sdk1.4.2_04\bin\java getJarPath
java.net.URl->file:/D:/getJarPath.class
getPath->/D:/getJarPath.class
getFile->/D:/getJarPath.class
getPath with . ->/C:/Program%20Files/exceed.nt/
3. D:\>D:\j2sdk1.4.2_04\bin\jar cvf getJarPath.jar getJarPath.class
4. D:\>D:\j2sdk1.4.2_04\bin\java -cp d:\getJarPath.jar getJarPath
java.net.URl->jar:file:/D:/getJarPath.jar!/getJarPath.class
getPath->file:/D:/getJarPath.jar!/getJarPath.class
getFile->file:/D:/getJarPath.jar!/getJarPath.class
Exception in thread "main" java.lang.NullPointerException
at getJarPath.main(getJarPath.java:15)
question:
in step 2. why the path "." is "/C:/Program%20Files/exceed.nt/" ?
in step 4. why NullPointerException occured?
thank a lot
BR

Your output seems to indicate that all lines executed successfully, yet you say there's a NullPointerException. Which is it?

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