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<chapter id="autoboxing" xreflabel="Autoboxing and Unboxing">
<title>Autoboxing and Unboxing</title>
<sect1 id="boxing-inJava5">
<title>Autoboxing and Unboxing in Java 5</title>
<para>
Java 5 (and hence AspectJ 1.5) supports automatic conversion of
primitive types (int, float, double etc.) to their object equivalents
(Integer, Float, Double,...) in assignments and method and constructor
invocations. This conversion is know as autoboxing.
</para>
<para>Java 5 also supports automatic unboxing, where wrapper types
are automatically converted into their primitive equivalents if
needed for assignments or method or constructor invocations.</para>
<para>For example:</para>
<programlisting><![CDATA[
int i = 0;
i = new Integer(5); // auto-unboxing
Integer i2 = 5; // autoboxing
]]></programlisting>
</sect1>
<sect1 id="autoboxing-in-aspectj5">
<title>Autoboxing and Join Point matching in AspectJ 5</title>
<para>Most of the pointcut designators match based on signatures, and
hence are unaffected by autoboxing. For example, a call to a method</para>
<programlisting><![CDATA[
public void foo(Integer i);
]]></programlisting>
<para>is <emphasis>not</emphasis> matched by a pointcut
<literal>call(void foo(int))</literal> since the signature declares
a single <literal>Integer</literal> parameter, not an <literal>int</literal>.
</para>
<para>The <literal>args</literal> pointcut designator is affected by
autoboxing since it matches based on the runtime type of the arguments.
AspectJ 5 applies autoboxing and unboxing in determining argument matching.
In other words, <literal>args(Integer)</literal> will match any join
point at which there is a single argument of type <literal>Integer</literal>
or of type <literal>int</literal>.</para>
<itemizedlist>
<listitem>args(Integer) and args(int) are equivalent</listitem>
<listitem>args(Float) and args(float) are equivalent</listitem>
<listitem>args(Double) and args(double) are equivalent</listitem>
<listitem>args(Short) and args(short) are equivalent</listitem>
<listitem>args(Byte) and args(byte) are equivalent</listitem>
<listitem>args(Long) and args(long) are equivalent</listitem>
<listitem>args(Boolean) and args(boolean) are equivalent</listitem>
</itemizedlist>
<para>
Autoboxing and unboxing are also applied when binding pointcut or
advice parameters, for example:
</para>
<programlisting><![CDATA[
pointcut foo(int i) : args(i);
before(Integer i) : foo(i) {
...
}
]]></programlisting>
</sect1>
<sect1 id="autoboxing-and-method-dispatch">
<title>Inter-type method declarations and method dispatch</title>
<para>Autoboxing, unboxing, and also varargs all affect the method
dispatch algorithm used in Java 5. In AspectJ 5, the target method
of a call is selected according to the following algorithm:</para>
<orderedlist>
<listitem>Attempt to locate a matching method or inter-type declared
method without considering
autoboxing, unboxing, or vararg invocations.</listitem>
<listitem>If no match is found, try again considering autoboxing
and unboxing.</listitem>
<listitem>Finally try again considering both autoboxing, unboxing,
and varargs.</listitem>
</orderedlist>
<para>One consequence is that a directly matching inter-type declared
method will take precedence over a method declared locally in the
target class but that only matches via autoboxing.</para>
</sect1>
</chapter>
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