How to return an instance from Enum?

Question

Note that I have an Algorithm enum as

 public enum Algorithm { SHA1("sha1"), HMAC("hmac"),; Algorithm(final String algorithm) { this.algorithm = algorithm; } private final String algorithm; public String getAlgorithm() { return algorithm; } } 

and I have different algorithms like

 public class Sha1 { public static String hash(final String text, final byte[] sb) {...} } 

and

 public class Hmac { public static String hash(final String text, final byte[] sb) {...} } 

I want to return my instances when someone calls for example

 Algorithm.SHA1.getInstance() 

Question

• How to return an instance since my method is static? (This is static, so multiple threads cannot interact with each other).

Answer 1

You cannot return an instance when your method is static, but you can make your enum interface implemented and create an instance method that invokes the static method, and does a virtual dispatch for you:

 public interface EncryptionAlgo { String hash(final String text, final byte[] sb); } public enum Algorithm implements EncryptionAlgo { SHA1("sha1") { public String hash(final String text, final byte[] sb) { return Sha1.hash(text, sb); } }, HMAC("hmac") { public String hash(final String text, final byte[] sb) { return Hmac.hash(text, sb); } }; Algorithm(final String algorithm) { this.algorithm = algorithm; } private final String algorithm; public String getAlgorithm() { return algorithm; } } 

Now you can call hash on the SHA1 or HMAC instance, for example:

 Algorithm.HMAC.hash(someText, sb); 

or bypass EncryptionAlgo instances, for example:

 EncryptionAlgo algo = Algorithm.SHA1;