code: public void clear() {
          Random r = new Random();
          if (privateKeyAsSeed != null) {
              for (int i=0; i< privateKeyAsSeed.length ; i++) {
                  privateKeyAsSeed[i] = (char)(r.nextInt(26) + 'a');
              }
              Arrays.fill(privateKeyAsSeed, '\0');
          }
          if (publicKey != null) {
              for (int i=0; i< publicKey.length ; i++) {
                  publicKey[i] = (char)(r.nextInt(26) + 'a');
              }
              Arrays.fill(publicKey, '\0');
          }
      }
docs: Clear the seed and public key char arrays by filling them
  with random bytes then zero-ing them out.
  
  The nkey is unusable after this operation.