Enum is causing ExceptionInInitializerError in Groovy 2.x - exception

Question

My enum:
enum ServiceEnvironment implements ServiceEnvironmentStatics {
Local(LOCAL_URI),
Sandbox(SANDBOX_URI),
Production(PRODUCTION_URI)
private final String uri
private ServiceEnvironment(String uri) {
super()
this.uri = uri
}
}
interface ServiceEnvironmentStatics {
static final String LOCAL_URI = "localhost:8080"
static final String SANDBOX_URI = "sandbox.myapi.example.com"
static final String PRODUCTION_URI = "myapi.example.com"
}
When I use this in code like so:
ServiceEnvironment env = ServiceEnvironment.Local
I get:
Caused by: groovy.lang.GroovyRuntimeException: Could not find matching constructor for: com.me.myapp.ServiceEnvironment(java.lang.String, java.lang.Integer, java.lang.String)
at groovy.lang.MetaClassImpl.selectConstructorAndTransformArguments1(MetaClassImpl.java:1490)
at groovy.lang.MetaClassImpl.selectConstructorAndTransformArguments(MetaClassImpl.java:1409)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.selectConstructorAndTransformArguments(ScriptBytecodeAdapter.java:234)
at com.me.myapp.ServiceEnvironment.$INIT(ServiceEnvironment.groovy)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:90)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:233)
at org.codehaus.groovy.runtime.callsite.StaticMetaMethodSite.invoke(StaticMetaMethodSite.java:43)
at org.codehaus.groovy.runtime.callsite.StaticMetaMethodSite.callStatic(StaticMetaMethodSite.java:99)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCallStatic(CallSiteArray.java:53)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callStatic(AbstractCallSite.java:157)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callStatic(AbstractCallSite.java:173)
at com.me.myapp.ServiceEnvironment.<clinit>(ServiceEnvironment.groovy)
... 36 more
What's going on?

Answer 1

tl;dr: Remove the super() invocation from your enum constructor.
The Actual Answer: The sole superclass of all enum classes is java.lang.Enum, which does not have a no-argument constructor. Therefore the line super() is in error. The runtime error here is rather misleading, due to the nature of dynamic method/constructor dispatch in Groovy. If we were instead to try to compile a roughly equivalent enum class in Java:
public enum ServiceEnvironment {
Local("localhost:8080"),
Sandbox("sandbox.myapi.example.com"),
Production("myapi.example.com");
private final String uri;
private ServiceEnvironment(String uri) {
super();
this.uri = uri;
}
}
The compiler would directly tell us that the super() statement is the problem. My Java compiler says:
Cannot invoke super constructor from enum constructor ServiceEnvironment(String)
...which makes much more sense at compile-time than the message that Groovy is giving at runtime.