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<p>This is described <a href="http://groovy.codehaus.org/Differences+from+Java">here</a>.</p>

<p>Basically in Java == with primitive types means use equality. For object types == means test identity.</p>

<p>We found when working with Groovy that if we kept those semantics and folks used dynamic typing as follows</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>
def x = 2 * 2
if (x == 4) {
...
}
</pre></td></tr></table>
<p>They would get surprising results, as they often mean equality based on value, such as in the above, rather than identity. Indeed folks rarely ever use identity comparisions.</p>

<p>So to avoid many common gotchas and confusions, we've made == mean equals, the meaning most developers use, and we use this for both primitive types and for object types and across both static and dynamic typing to simplify things.</p>

<p>Currently if you really want to compare identities of the objects, use the method is(), which is provided by every object.</p>
<table class="wysiwyg-macro" data-macro-name="noformat" style="background-image: url(/plugins/servlet/confluence/placeholder/macro-heading?definition=e25vZm9ybWF0fQ&amp;locale=en_GB&amp;version=2); background-repeat: no-repeat;" data-macro-body-type="PLAIN_TEXT"><tr><td class="wysiwyg-macro-body"><pre>
if (x.is(4)) {
... // never true
}
</pre></td></tr></table>
<p> The above condition is never true, since the Integer object in x (which is the result of the computation above) is not identical to the Integer object with value 4 that has been created for the comparison.</p>