fix bugs in File.getParent and listFiles

getParent should return the same value regardless of whether it ends
in a file separator, and listFiles should return null for
non-directories.

classpath/java/io/File.java

@@ -148,9 +148,13 @@ public class File implements Serializable {
   }
 
   public String getParent() {
-    int index = path.lastIndexOf(FileSeparator);
+    String p = path;
+    while (p.endsWith(FileSeparator)) {
+      p = p.substring(0, p.length() - 1);
+    }
+    int index = p.lastIndexOf(FileSeparator);
     if (index >= 0) {
-      return path.substring(0, index);
+      return p.substring(0, index);
     } else {
       return null;
     }    
@@ -239,11 +243,15 @@ public class File implements Serializable {
 
   public File[] listFiles(FilenameFilter filter) {
     String[] list = list(filter);
+    if (list != null) {
       File[] result = new File[list.length];
       for (int i = 0; i < list.length; ++i) {
         result[i] = new File(this, list[i]);
       }
       return result;
+    } else {
+      return null;
+    }
   }
 
   public String[] list() {
@@ -254,6 +262,7 @@ public class File implements Serializable {
     long handle = 0;
     try {
       handle = openDir(path);
+      if (handle != 0) {
         Pair list = null;
         int count = 0;
         for (String s = readDir(handle); s != null; s = readDir(handle)) {
@@ -270,6 +279,9 @@ public class File implements Serializable {
         }
 
         return result;
+      } else {
+        return null;
+      }
     } finally {
       if (handle != 0) {
         closeDir(handle);

test/Files.java

@@ -74,6 +74,12 @@ public class Files {
         f.delete();
       }
     }
+
+    expect(new File("foo/bar").getParent().equals("foo"));
+    expect(new File("foo/bar/").getParent().equals("foo"));
+    expect(new File("foo/bar//").getParent().equals("foo"));
+
+    expect(new File("foo/nonexistent-directory").listFiles() == null);
   }
 
 }