How to destroy Java PrivateKey

The default PrivateKey.destroy() may not be implemented

private static void xor(byte[] p, byte[] key) {
  for (int i=0; i < p.length; i++) {
   p[i] = (byte)(p[i] ^ key[i % key.length]);
  }  
 }
 
 public final static void main(String[] args) throws Exception {
  KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
  keyPairGenerator.initialize(4096);
  KeyPair kp = keyPairGenerator.generateKeyPair();
  byte[] encKey = kp.getPrivate().getEncoded();
  byte[] text = "This is a sample text!".getBytes();
  xor(text, encKey);
  PrivateKey pk = kp.getPrivate();
  try {
   pk.destroy();
  }
  catch (Exception e) {
   Field keyField = sun.security.pkcs.PKCS8Key.class.getDeclaredField("key");
   keyField.setAccessible(true);
   keyField.set(pk, new byte[] { 0 });
   Field encodedField = sun.security.pkcs.PKCS8Key.class.getDeclaredField("encodedKey");
   encodedField.setAccessible(true);
   encodedField.set(pk, null);
   RSAPrivateKey asRsa = (RSAPrivateKey) pk;
   clear(asRsa.getModulus());
   clear(asRsa.getPrivateExponent());
  }
  xor(text, pk.getEncoded());
  System.out.println(new String(text));  
 }

 private static void clear(BigInteger bigInt) throws Exception {
  Field valField = bigInt.getClass().getDeclaredField("mag");
  valField.setAccessible(true);
  valField.set(bigInt, new int[] { 0 });  
 }

The output is garbage: dê`1"hsl&zKë8ê’-udyq!

It means that we destroyed Private Key material properly.