org.aspectj/docs/adk15notebook/autoboxing.adoc

[[autoboxing]]
= Autoboxing and Unboxing

[[boxing-inJava5]]
== Autoboxing and Unboxing in Java 5

Java 5 (and hence AspectJ 1.5) supports automatic conversion of
primitive types (`int`, `float`, `double` etc.) to their object equivalents
(`Integer`, `Float`, `Double` etc.) in assignments and method and constructor
invocations. This conversion is know as autoboxing.

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.

For example:

[source, java]
....
int i = 0;
i = new Integer(5);  // auto-unboxing
Integer i2 = 5;      // autoboxing
....

[[autoboxing-in-aspectj5]]
== Autoboxing and Join Point matching in AspectJ 5

Most of the pointcut designators match based on signatures, and hence
are unaffected by autoboxing. For example, a call to a method

[source, java]
....
public void foo(Integer i);
....

is _not_ matched by a pointcut `call(void foo(int))` since the signature
declares a single `Integer` parameter, not an `int`.

The `args` 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, `args(Integer)` will match any join point at which there is a
single argument of type `Integer` or of type `int`.

* `args(Integer)` and `args(int)` are equivalent
* `args(Float)` and `args(float)` are equivalent
* `args(Double)` and `args(double)` are equivalent
* `args(Short)` and `args(short)` are equivalent
* `args(Byte)` and `args(byte)` are equivalent
* `args(Long)` and `args(long)` are equivalent
* `args(Boolean)` and `args(boolean)` are equivalent

Autoboxing and unboxing are also applied when binding pointcut or advice
parameters, for example:

[source, java]
....
pointcut foo(int i) : args(i);

before(Integer i) : foo(i) {
  // ...
}
....

[[autoboxing-and-method-dispatch]]
== Inter-type method declarations and method dispatch

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:

[arabic]
. Attempt to locate a matching method or inter-type declared method
without considering autoboxing, unboxing, or vararg invocations.
. If no match is found, try again considering autoboxing and unboxing.
. Finally try again considering both autoboxing, unboxing, and varargs.

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.