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[headius @ cnutter:~/projects/jruby-rack]
◆ cat Foo.java
public interface Foo {
  public Runnable getRunnable();
}
[headius @ cnutter:~/projects/jruby-rack]
◆ cat FooEater.java
public class FooEater {
  private Foo foo;
  public FooEater(Foo foo) {
    this.foo = foo;
  }
  public Runnable getRunnable() {
    return foo.getRunnable();
  }
}
[headius @ cnutter:~/projects/jruby-rack]
◆ jruby -rjava -e "o = Object.new; def o.getRunnable; o = Object.new; def o.run; puts 'here'; end; end; t = java.lang.Thread.new(Java::FooEater.new(o).getRunnable); t.start; t.join"
java/lang/Thread.java:349:in `init': java.lang.NullPointerException: null (NativeException)
	from java/lang/Thread.java:429:in `<init>'
	from sun/reflect/NativeConstructorAccessorImpl.java:-2:in `newInstance0'
	from sun/reflect/NativeConstructorAccessorImpl.java:39:in `newInstance'
	from sun/reflect/DelegatingConstructorAccessorImpl.java:27:in `newInstance'
	from java/lang/reflect/Constructor.java:513:in `newInstance'
	from org/jruby/javasupport/JavaConstructor.java:226:in `new_instance'
	from org/jruby/java/invokers/ConstructorInvoker.java:100:in `call'
	from org/jruby/java/invokers/ConstructorInvoker.java:180:in `call'
	 ... 16 levels...
	from org/jruby/Main.java:214:in `run'
	from org/jruby/Main.java:100:in `run'
	from org/jruby/Main.java:84:in `main'
Complete Java stackTrace
java.lang.NullPointerException
	at java.lang.Thread.init(Thread.java:349)
	at java.lang.Thread.<init>(Thread.java:429)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
	at org.jruby.javasupport.JavaConstructor.new_instance(JavaConstructor.java:226)
	at org.jruby.java.invokers.ConstructorInvoker.call(ConstructorInvoker.java:100)
	at org.jruby.java.invokers.ConstructorInvoker.call(ConstructorInvoker.java:180)
	at org.jruby.RubyClass.finvoke(RubyClass.java:372)
	at org.jruby.javasupport.util.RuntimeHelpers.invoke(RuntimeHelpers.java:288)
	at org.jruby.java.proxies.ConcreteJavaProxy$2.call(ConcreteJavaProxy.java:48)
	at org.jruby.runtime.callsite.CachingCallSite.cacheAndCall(CachingCallSite.java:290)
	at org.jruby.runtime.callsite.CachingCallSite.call(CachingCallSite.java:126)
	at org.jruby.RubyClass$SpecificArityNew.call(RubyClass.java:555)
	at org.jruby.internal.runtime.methods.DynamicMethod.call(DynamicMethod.java:152)
	at org.jruby.java.proxies.ConcreteJavaProxy$ConcreteNewMethod.call(ConcreteJavaProxy.java:170)
	at org.jruby.runtime.callsite.CachingCallSite.cacheAndCall(CachingCallSite.java:280)
	at org.jruby.runtime.callsite.CachingCallSite.call(CachingCallSite.java:116)
	at ruby.__dash_e__.__file__(-e:1)
	at ruby.__dash_e__.__file__(-e)
	at ruby.__dash_e__.load(-e)
	at org.jruby.Ruby.runScript(Ruby.java:564)
	at org.jruby.Ruby.runNormally(Ruby.java:467)
	at org.jruby.Ruby.runFromMain(Ruby.java:340)
	at org.jruby.Main.run(Main.java:214)
	at org.jruby.Main.run(Main.java:100)
	at org.jruby.Main.main(Main.java:84)