It returns an ECGenParameterSpec object using the OID as its name.

$ cat A2.java
import java.security.AlgorithmParameters;
import java.security.KeyPairGenerator;
import java.security.spec.ECGenParameterSpec;

public class A2 {
    public static void main(String[] args) throws Exception {
        var k = KeyPairGenerator.getInstance("EC").generateKeyPair().getPublic();
        var a = AlgorithmParameters.getInstance("EC");
        a.init(k.getParams());
        System.out.println(a.getParameterSpec(ECGenParameterSpec.class).getName());
    }
}
$ java A2.java
1.3.132.0.34