public static int hashCode(Object obj) {
        // hashCode(Object) retained for performance, as hash code is often critical
        return obj == null ? 0 : obj.hashCode();
    }
<p>Gets the hash code of an object returning zero when the
object is {@code null}.</p>

<pre>
ObjectUtils.hashCode(null)   = 0
ObjectUtils.hashCode(obj)    = obj.hashCode()
</pre>

@param obj  the object to obtain the hash code of, may be {@code null}
@return the hash code of the object, or zero if null
@since 2.1
android/android_framework/base/src/main/java/lang3/ObjectUtils.java