Creating new Java object instantiation error

Question

I am trying to create a new SimpleLinkResolver in Clojure. This is the JavaDoc:

http://prismicio.github.io/java-kit/io/prismic/SimpleLinkResolver.html

My clojure code is:

(def lr (new io.prismic.SimpleLinkResolver))

but at the repl I get the following error:

CompilerException java.lang.InstantiationException, compiling:(form-init460449823042827832.clj:1:1)

I have no problem creating a java.util.Date:

(def d (new java.util.Date))
=> #'prismic-clojure.core/d
d
=> #inst"2018-03-17T10:30:36.016-00:00"

The above JavaDoc does say that SimpleLinkResolver is deprecated because the interface LinkResolver (http://prismicio.github.io/java-kit/io/prismic/LinkResolver.html) has default methods and so can be implemented directly. So I gave this a go to:

(def lr (new io.prismic.LinkResolver))
CompilerException java.lang.IllegalArgumentException: No matching ctor found for interface io.prismic.LinkResolver,

And I get this "no ctor" error - which I am guessing means the compiler can't find a constructor?

Questions:

Why does the first effort produce an InstantiationException?
Not being familiar with the Java-8 default methods, how would I create a new LinkResolver using its default methods?

Thanks

Taylor Wood · Accepted Answer · 2018-03-17 11:10:34Z

3

Why does the first effort produce an InstantiationException?

You can't instantiate an abstract class:

public abstract class SimpleLinkResolver

Not being familiar with the Java-8 default methods, how would I create a new LinkResolver using its default methods?

You'll need to implement LinkResolver interface, which can be done using Clojure's reify:

(def resolver
  (reify LinkResolver
    (^String resolve [this ^Fragment$DocumentLink link]
      "a string"))) ;; put actual impl. here
(.resolve resolver nil)
;; => "a string"

Note you need to type-hint the return value (and arguments) because .resolve() is an overloaded method.

Also, you typically see (Class.) dot-syntax rather than (new Class) to instantiate Java classes.

edited Mar 17, 2018 at 11:10

answered Mar 17, 2018 at 10:56

Taylor Wood

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1 Comment

Zuriar Over a year ago

thank you for your very informative answer. Much appreciated!

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