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package trusted;
import untrusted.RetValue;

public class MixMatch {
  private void privilegedMethod() throws IOException {
    try {
      AccessController.doPrivileged(
        new PrivilegedExceptionAction<FileInputStream>PrivilegedExceptionAction<Void>() {
          public FileInputStreamVoid run() throws IOException, FileNotFoundException {
            final FileInputStream fis = new FileInputStream("file.txt");
            try {
              RetValue rt = new RetValue();

              if (rt.getValue() == 1) {
                // do something with sensitive file
              }
            } finally {
              fis.close();
            }
   ??????return fis;         return null; // nothing to return.
          }
        }
      );
    } catch (PrivilegedActionException e) {
      // forward to handler and log
    }
  }

  public static void main(String[] args) throws IOException {
    MixMatch mm = new MixMatch();
    mm.privilegedMethod();
  }
}

// In another JAR file:
package untrusted;

class RetValue {
  public int getValue() {
    return 1;
  }
}