code: public KeyPair getKeyPair() throws GeneralSecurityException, IOException {
          if (privateKeyAsSeed == null) {
              throw new IllegalStateException("Public-only NKey");
          }
  
          DecodedSeed decoded = decodeSeed(privateKeyAsSeed);
          byte[] seedBytes = new byte[ED25519_SEED_SIZE];
          byte[] pubBytes = new byte[ED25519_PUBLIC_KEYSIZE];
  
          System.arraycopy(decoded.bytes, 0, seedBytes, 0, seedBytes.length);
          System.arraycopy(decoded.bytes, seedBytes.length, pubBytes, 0, pubBytes.length);
  
          EdDSAPrivateKeySpec privKeySpec = new EdDSAPrivateKeySpec(seedBytes, NKey.ed25519);
          EdDSAPrivateKey privKey = new EdDSAPrivateKey(privKeySpec);
          EdDSAPublicKeySpec pubKeySpec = new EdDSAPublicKeySpec(pubBytes, NKey.ed25519);
          EdDSAPublicKey pubKey = new EdDSAPublicKey(pubKeySpec);
  
          return new KeyPair(pubKey, privKey);
      }
docs: @return A Java security keypair that represents this NKey in Java security
  form.
  
  @throws GeneralSecurityException if there is an encryption problem
  @throws IOException              if there is a problem encoding or decoding