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

Answer: 
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}$");
}

```
**RegExp SHA-1** 

```
public static final String SHA_1 = "^([0-9A-Fa-f]{2}[:]){19}([0-9A-Fa-f]{2})$";

public boolean isValidSHA1(String s) {
    return s.matches(SHA_1);
}

boolean isValidSHA1 = isValidSHA1("12:45:54:3A:99:24:52:EA...");

```