what's the exact format "KeyProvider loadKeys(String privateKey, String publicKey, PasswordFinder passwordFinder)' that want

In my case, I have to ssh via publickey for secure issue, when I using SSHClient#loadKeys(String privateKey, String publicKey, PasswordFinder passwordFinder) method, I don't know what kind of format it want, it says it need private key with PKCS8, but what about the public key format? I try some combinations but it doesn't work and says "Exhausted available authentication methods". thanks your time for this issue.