How do I check if a string is a valid md5 or sha1 checksum string

Question

I don't want to calculate a file's checksum, just to know if a given string is a valid checksum

Answer 1

Any 160-bit sequence is a possible SHA1 hash. Any 128-bit sequence is a possible MD5 hash.

If you're looking at the hex string representations of them, then a sha1 will look like 40 hexadecimal digits, and an md5 will look like 32 hexadecimal digits.

Answer 2

SHA1 verifier:

public boolean isValidSHA1(String s) {
    return s.matches("[a-fA-F0-9]{40}");
}

MD5 verifier:

public boolean isValidMD5(String s) {
    return s.matches("[a-fA-F0-9]{32}");
}