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<h1>Evaluating the MetaClass runtime</h1>

<p>Since 1.1, Groovy supports a much richer set of APIs for evaluating the MetaClass runtime. Using these APIs in combination with <a class="confluence-link" href="/display/GROOVY/ExpandoMetaClass" data-linked-resource-id="79517" data-linked-resource-type="page" data-linked-resource-default-alias="ExpandoMetaClass" data-base-url="http://docs.codehaus.org">ExpandoMetaClass</a> makes Groovy an extremely powerful language for meta-programming</p>

<h2>Finding out methods and properties</h2>

<p>To obtain a list of methods ( or <a href="http://groovy.codehaus.org/api/groovy/lang/MetaMethod.html">MetaMethod</a> instances in Groovy speak) for a particular Groovy class use can inspect its MetaClass:</p>

<table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
println obj.metaClass.methods
println obj.metaClass.methods.find { it.name.startsWith("to") }
</pre></td></tr></table>

<p>The same can be done for properties:</p>

<table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
println obj.metaClass.properties
println obj.metaClass.properties.find { it.name.startsWith("to") }
</pre></td></tr></table>

<h2>Using respondsTo and hasProperty</h2>

<p>Obtaining a list of methods sometimes is a little more than what you want. It is quite common in meta-programming scenarios to want to find out if an object supports a particular method.</p>

<p>Since 1.1, you can use respondsTo and hasProperty to achieve this:</p>

<table class="wysiwyg-macro" data-macro-name="code" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e2NvZGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
class Foo {
   String prop
   def bar() { "bar" }
   def bar(String name) { "bar $name" }
   def add(Integer one, Integer two) { one + two}
}

def f = new Foo()

if(f.metaClass.respondsTo(f, "bar")) {
   // do stuff
}

if(f.metaClass.respondsTo(f, "bar", String)) {
   // do stuff
}

if(!f.metaClass.respondsTo(f, "bar", Integer)) {
   // do stuff
}

if(f.metaClass.respondsTo(f, "add", Integer, Integer)) {
   // do stuff
}

if(f.metaClass.hasProperty(f, "prop")) {
  // do stuff
}
</pre></td></tr></table>

<p>The respondsTo method actually returns a List of MetaMethod instances so you can use it to both query and evaluate the resulting list. </p>

<table class="wysiwyg-macro" data-macro-name="note" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e25vdGV9&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="RICH_TEXT"><tr><td class="wysiwyg-macro-body">
<p>respondsTo only works for &quot;real&quot; methods and those added via <a class="confluence-link" href="/display/GROOVY/ExpandoMetaClass" data-linked-resource-id="79517" data-linked-resource-type="page" data-linked-resource-default-alias="ExpandoMetaClass" data-base-url="http://docs.codehaus.org">ExpandoMetaClass</a> and not for cases where you override invokeMethod or methodMissing. It is impossible in these cases to tell if an object responds to a method without actually invoking the method.</p></td></tr></table>