Issue 4231 - Fix unstable FilterEngineTest.testSetRemoveFilterChangeCallback

libadblockplus-android/src/org/adblockplus/libadblockplus/FileSystem.java

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2017 eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 53 matching lines @@
       return lastModified;
     }
 
     public StatResult(boolean exists, boolean isDirectory, boolean isFile, long lastModified)
     {
       this.exists = exists;
       this.isDirectory = isDirectory;
       this.isFile = isFile;
       this.lastModified = lastModified;
     }
+
+    @Override
+    public String toString()
+    {
+      return "StatResult{" +
+        "exists=" + exists +
+        ", isDirectory=" + isDirectory +
+        ", isFile=" + isFile +
+        ", lastModified=" + lastModified +
+        '}';
+    }
   }
 
   /**
    * Reads from a file.
    * @param path File path.
-   * @return File's content as string
+   * @return File's binary data.
    */
-  public abstract String read(String path);
+  public abstract byte[] read(String path);
 
   /**
    * Writes to a file.
    * @param path File path.
-   * @param data File data to write.
+   * @param data File's binary data to write.
    */
-  public abstract void write(String path, String data);
+  public abstract void write(String path, byte[] data);
 
   /**
    * Moves a file (i.e.\ renames it).
    * @param fromPath Current path to the file.
    * @param toPath New path to the file.
    */
   public abstract void move(String fromPath, String toPath);
 
   /**
    * Removes a file.
@@ skipping 36 matching lines @@
       dtor(this.ptr);
     }
   }
 
   private final static native void registerNatives();
 
   private final static native long ctor(Object callbackObject);
 
   private final static native void dtor(long ptr);
 }