The mapping from Lisp to Java is not always obvious, for example because a Lisp integer can map to
byte. In most cases, like method calls, the target Java type is known. In these cases, LispWorks allows
integer in the acceptable range for
char, any Lisp float for
When the target is not known, like storing a value in a Java array object (that is type
java.lang.Object) or using lisp-to-jobject, LispWorks uses this mapping:
LispWorks has a set of keywords and FLI types to match the primitive types, which can be used to specify these types, for example as the type of an array. The keyword names are the Java name (uppercased), and the FLI type names are the Java name preceded by J (and uppercased), exported from LW-JI. These are shown in the table below.
The Java type
char (and hence the class
Character) corresponds to UTF-16 code units. which is equivalent to
unsigned short. It does not correspond to Unicode characters, and therefore cannot be mapped to LispWorks characters.
LispWorks deals specially with
java.lang.String objects, converting them automatically to Lisp strings when receiving them (return value of methods or arguments to calls into Lisp), and converting Lisp strings to
java.lang.String when passing them (argument to method calls, return values from calls into Lisp). It is therefore possible to think of strings as another primitive type. The overhead associated with this conversion for short strings (tens of characters) is smaller than the overhead associated with passing a Java non-primitive object. Even for larger strings, the fact that all the data in the string is passed in one call without further Java/Lisp interaction make it an effective way of passing data.
All Java non-primitive objects are represented in LispWorks as foreign pointers of type jobject. jobject is a proper Lisp type, that is you can use
cl:typep and specialize methods on it. The actual Java class of the object is not consistently represented, unless you explicitly ask for it using jobject-class-name. You can get a string describing the Java object in the way that Java "thinks" (that is the result of
toString) using jobject-string. If you need a Java null value, then you can use the constant *java-null*.
Instances of standard-java-object are also considered to represent Java objects. standard-java-object instances have a slot that contains the actual jobject, which is used when an instance of standard-java-object is passed to the interface functions. In the text below, when argument is specified as "java-object" or "Java object", it can be either a jobject or an instance of standard-java-object.
LispWorks User Guide and Reference Manual - 20 Sep 2017