Blackberry 实例化接口时出错

以下代码无法编译并显示消息：

无法实例化SymmetricKey类型
接口。我该如何解决这个问题

 ByteArrayOutputStream baos = new ByteArrayOutputStream(); 
 InitializationVector iv = new InitializationVector("helo".getBytes());
 SymmetricKey key = new SymmetricKey("AES_256","key", 0, "key".length());
 OutputStream os = EncryptorFactory.getEncryptorOutputStream(key, baos, "AES/CBC/PKCS5",);
 os.write("somedata".getBytes());
 byte[] encryptedData = baos.toByteArray();
 ByteArrayInputStream bais = new ByteArrayInputStream(encryptedData);
 InputStream is = DecryptorFactory.getDecryptorInputStream(key, bais, "AES/CBC/PKCS5", iv); 

我使用SymmetricKeyFactory解决了我的问题

SymmetricKey key=
    SymmetricKeyFactory.getInstance("AES_256","key".getBytes(), 0, "abc123".length());