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);
-    File[] result = new File[list.length];
-    for (int i = 0; i < list.length; ++i) {
-      result[i] = new File(this, list[i]);
+    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;
     }
-    return result;
   }
 
   public String[] list() {
@@ -254,22 +262,26 @@ public class File implements Serializable {
     long handle = 0;
     try {
       handle = openDir(path);
-      Pair list = null;
-      int count = 0;
-      for (String s = readDir(handle); s != null; s = readDir(handle)) {
-        if (filter == null || filter.accept(this, s)) {
-          list = new Pair(s, list);
-          ++ count;
+      if (handle != 0) {
+        Pair list = null;
+        int count = 0;
+        for (String s = readDir(handle); s != null; s = readDir(handle)) {
+          if (filter == null || filter.accept(this, s)) {
+            list = new Pair(s, list);
+            ++ count;
+          }
         }
-      }
 
-      String[] result = new String[count];
-      for (int i = count - 1; i >= 0; --i) {
-        result[i] = list.value;
-        list = list.next;
-      }
+        String[] result = new String[count];
+        for (int i = count - 1; i >= 0; --i) {
+          result[i] = list.value;
+          list = list.next;
+        }
 
-      return result;
+        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);
   }
 
 }