From: Nic Ferrier Date: Fri, 1 Feb 2002 23:43:35 +0000 (+0000) Subject: * gcj.texi (About CNI): New node. X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=ca6b827f15363a172395ccf8bac434d482a2ff2f;p=gcc.git * gcj.texi (About CNI): New node. From-SVN: r49417 --- diff --git a/gcc/java/gcj.texi b/gcc/java/gcj.texi index 3c3f4d2e9c3..3e9f31cf134 100644 --- a/gcc/java/gcj.texi +++ b/gcc/java/gcj.texi @@ -123,6 +123,7 @@ files and object files, and it can read both Java source code and * Invoking jcf-dump:: Print information about class files * Invoking gij:: Interpreting Java bytecodes * Invoking jv-convert:: Converting from one encoding to another +* About CNI:: Description of the Cygnus Native Interface * Resources:: Where to look for more information @end menu @@ -395,7 +396,7 @@ question actually does violate array bounds constraints. @item -fjni With @code{gcj} there are two options for writing native methods: CNI -and JNI. By default @code{gcj} assumes you are using CNI. If you are +and JNI@. By default @code{gcj} assumes you are using CNI@. If you are compiling a class with native methods, and these methods are implemented using JNI, then you must use @code{-fjni}. This option causes @code{gcj} to generate stubs which will invoke the underlying JNI @@ -831,6 +832,874 @@ Print version information, then exit. @c man end +@node About CNI +@chapter About CNI + +This documents CNI, the Cygnus Native Interface, +which is is a convenient way to write Java native methods using C++. +This is a more efficient, more convenient, but less portable +alternative to the standard JNI (Java Native Interface). + +@menu +* Basic concepts:: Introduction to using CNI@. +* Packages:: How packages are mapped to C++. +* Primitive types:: Handling Java types in C++. +* Interfaces:: How Java interfaces map to C++. +* Objects and Classes:: C++ and Java classes. +* Class Initialization:: How objects are initialized. +* Object allocation:: How to create Java objects in C++. +* Arrays:: Dealing with Java arrays in C++. +* Methods:: Java methods in C++. +* Strings:: Information about Java Strings. +* Mixing with C++:: How CNI can interoperate with C++. +* Exception Handling:: How exceptions are handled. +* Synchronization:: Synchronizing between Java and C++. +* Reflection:: Using reflection from C++. +@end menu + + +@node Basic concepts +@section Basic concepts + +In terms of languages features, Java is mostly a subset +of C++. Java has a few important extensions, plus a powerful standard +class library, but on the whole that does not change the basic similarity. +Java is a hybrid object-oriented language, with a few native types, +in addition to class types. It is class-based, where a class may have +static as well as per-object fields, and static as well as instance methods. +Non-static methods may be virtual, and may be overloaded. Overloading is +resolved at compile time by matching the actual argument types against +the parameter types. Virtual methods are implemented using indirect calls +through a dispatch table (virtual function table). Objects are +allocated on the heap, and initialized using a constructor method. +Classes are organized in a package hierarchy. + +All of the listed attributes are also true of C++, though C++ has +extra features (for example in C++ objects may be allocated not just +on the heap, but also statically or in a local stack frame). Because +@code{gcj} uses the same compiler technology as G++ (the GNU +C++ compiler), it is possible to make the intersection of the two +languages use the same ABI (object representation and calling +conventions). The key idea in CNI is that Java objects are C++ +objects, and all Java classes are C++ classes (but not the other way +around). So the most important task in integrating Java and C++ is to +remove gratuitous incompatibilities. + +You write CNI code as a regular C++ source file. (You do have to use +a Java/CNI-aware C++ compiler, specifically a recent version of G++.) + +@noindent A CNI C++ source file must have: + +@example +#include +@end example + +@noindent and then must include one header file for each Java class it uses, e.g.: + +@example +#include +#include +#include +@end example + +@noindent These header files are automatically generated by @code{gcjh}. + + +CNI provides some functions and macros to make using Java objects and +primitive types from C++ easier. In general, these CNI functions and +macros start with the @code{Jv} prefix, for example the function +@code{JvNewObjectArray}. This convention is used to avoid conflicts +with other libraries. Internal functions in CNI start with the prefix +@code{_Jv_}. You should not call these; if you find a need to, let us +know and we will try to come up with an alternate solution. (This +manual lists @code{_Jv_AllocBytes} as an example; CNI should instead +provide a @code{JvAllocBytes} function.) + + +@subsection Limitations + +Whilst a Java class is just a C++ class that doesn't mean that you are +freed from the shackles of Java, a @acronym{CNI} C++ class must adhere to the +rules of the Java programming language. + +For example: it is not possible to declare a method in a CNI class +that will take a C string (@code{char*}) as an argument, or to declare a +member variable of some non-Java datatype. + + +@node Packages +@section Packages + +The only global names in Java are class names, and packages. A +@dfn{package} can contain zero or more classes, and also zero or more +sub-packages. Every class belongs to either an unnamed package or a +package that has a hierarchical and globally unique name. + +A Java package is mapped to a C++ @dfn{namespace}. The Java class +@code{java.lang.String} is in the package @code{java.lang}, which is a +sub-package of @code{java}. The C++ equivalent is the class +@code{java::lang::String}, which is in the namespace @code{java::lang} +which is in the namespace @code{java}. + +@noindent Here is how you could express this: + +@example +(// @r{Declare the class(es), possibly in a header file:} +namespace java @{ + namespace lang @{ + class Object; + class String; + ... + @} +@} + +class java::lang::String : public java::lang::Object +@{ + ... +@}; +@end example + +@noindent The @code{gcjh} tool automatically generates the nessary namespace +declarations. + + +@subsection Leaving out package names + +Always using the fully-qualified name of a java class can be +tiresomely verbose. Using the full qualified name also ties the code +to a single package making code changes necessary should the class +move from one package to another. The Java @code{package} declaration +specifies that the following class declarations are in the named +package, without having to explicitly name the full package +qualifiers. The @code{package} declaration can be +followed by zero or more @code{import} declarations, which +allows either a single class or all the classes in a package to be +named by a simple identifier. C++ provides something similar with the +@code{using} declaration and directive. + +@noindent In Java: + +@example +import @var{package-name}.@var{class-name}; +@end example + +@noindent allows the program text to refer to @var{class-name} as a shorthand for +the fully qualified name: @code{@var{package-name}.@var{class-name}}. + + +@noindent To achieve the same effect C++, you have to do this: + +@example +using @var{package-name}::@var{class-name}; +@end example + + +@noindent Java can also cause imports on demand, like this: + +@example +import @var{package-name}.*; +@end example + +@noindent Doing this allows any class from the package @var{package-name} to be +refered to only by its class-name within the program text. + + +@noindent The same effect can be achieved in C++ like this: + +@example +using namespace @var{package-name}; +@end example + + +@node Primitive types +@section Primitive types + +Java provides 8 @dfn{primitives} types which represent integers, floats, +characters and booleans (and also the void type). C++ has its own +very similar concrete types. Such types in C++ however are not always +implemented in the same way (an int might be 16, 32 or 64 bits for example) +so CNI provides a special C++ type for each primitive Java type: + +@multitable @columnfractions .20 .25 .60 +@item @strong{Java type} @tab @strong{C/C++ typename} @tab @strong{Description} +@item @code{char} @tab @code{jchar} @tab 16 bit Unicode character +@item @code{boolean} @tab @code{jboolean} @tab logical (true or false) values +@item @code{byte} @tab @code{jbyte} @tab 8-bit signed integer +@item @code{short} @tab @code{jshort} @tab 16 bit signed integer +@item @code{int} @tab @code{jint} @tab 32 bit signed integer +@item @code{long} @tab @code{jlong} @tab 64 bit signed integer +@item @code{float} @tab @code{jfloat} @tab 32 bit IEEE floating point number +@item @code{double} @tab @code{jdouble} @tab 64 bit IEEE floating point number +@item @code{void} @tab @code{void} @tab no value +@end multitable + +When refering to a Java type You should always use these C++ typenames (e.g.: @code{jint}) +to avoid disappointment. + + +@subsection Reference types associated with primitive types + +In Java each primitive type has an associated reference type, +e.g.: @code{boolean} has an associated @code{java.lang.Boolean} class. +In order to make working with such classes easier GCJ provides the macro +@code{JvPrimClass}: + +@deffn macro JvPrimClass type +Return a pointer to the @code{Class} object corresponding to the type supplied. + +@example +JvPrimClass(void) @result{} java.lang.Void.TYPE +@end example + +@end deffn + + +@node Interfaces +@section Interfaces + +A Java class can @dfn{implement} zero or more +@dfn{interfaces}, in addition to inheriting from +a single base class. + +@acronym{CNI} allows CNI code to implement methods of interfaces. +You can also call methods through interface references, with some +limitations. + +@acronym{CNI} doesn't understand interface inheritance at all yet. So, +you can only call an interface method when the declared type of the +field being called matches the interface which declares that +method. The workaround is to cast the interface reference to the right +superinterface. + +For example if you have: + +@example +interface A +@{ + void a(); +@} + +interface B extends A +@{ + void b(); +@} +@end example + +and declare a variable of type @code{B} in C++, you can't call +@code{a()} unless you cast it to an @code{A} first. + +@node Objects and Classes +@section Objects and Classes + +@subsection Classes + +All Java classes are derived from @code{java.lang.Object}. C++ does +not have a unique root class, but we use the C++ class +@code{java::lang::Object} as the C++ version of the +@code{java.lang.Object} Java class. All other Java classes are mapped +into corresponding C++ classes derived from @code{java::lang::Object}. + +Interface inheritance (the @code{implements} keyword) is currently not +reflected in the C++ mapping. + + +@subsection Object fields + +Each object contains an object header, followed by the instance fields +of the class, in order. The object header consists of a single +pointer to a dispatch or virtual function table. (There may be extra +fields @emph{in front of} the object, for example for memory +management, but this is invisible to the application, and the +reference to the object points to the dispatch table pointer.) + +The fields are laid out in the same order, alignment, and size as in +C++. Specifically, 8-bite and 16-bit native types (@code{byte}, +@code{short}, @code{char}, and @code{boolean}) are @emph{not} widened +to 32 bits. Note that the Java VM does extend 8-bit and 16-bit types +to 32 bits when on the VM stack or temporary registers. + +If you include the @code{gcjh}-generated header for a +class, you can access fields of Java classes in the @emph{natural} +way. For example, given the following Java class: + +@example +public class Int +@{ + public int i; + public Integer (int i) @{ this.i = i; @} + public static zero = new Integer(0); +@} +@end example + +you can write: + +@example +#include ; +#include ; + +Int* +mult (Int *p, jint k) +@{ + if (k == 0) + return Int::zero; // @r{Static member access.} + return new Int(p->i * k); +@} +@end example + + +@subsection Access specifiers + +CNI does not strictly enforce the Java access +specifiers, because Java permissions cannot be directly mapped +into C++ permission. Private Java fields and methods are mapped +to private C++ fields and methods, but other fields and methods +are mapped to public fields and methods. + + + +@node Class Initialization +@section Class Initialization + +Java requires that each class be automatically initialized at the time +of the first active use. Initializing a class involves +initializing the static fields, running code in class initializer +methods, and initializing base classes. There may also be +some implementation specific actions, such as allocating +@code{String} objects corresponding to string literals in +the code. + +The GCJ compiler inserts calls to @code{JvInitClass} at appropriate +places to ensure that a class is initialized when required. The C++ +compiler does not insert these calls automatically---it is the +programmer's responsibility to make sure classes are initialized. +However, this is fairly painless because of the conventions assumed by +the Java system. + +First, @code{libgcj} will make sure a class is initialized +before an instance of that object is created. This is one +of the responsibilities of the @code{new} operation. This is +taken care of both in Java code, and in C++ code. (When the G++ +compiler sees a @code{new} of a Java class, it will call +a routine in @code{libgcj} to allocate the object, and that +routine will take care of initializing the class.) It follows that you can +access an instance field, or call an instance (non-static) +method and be safe in the knowledge that the class and all +of its base classes have been initialized. + +Invoking a static method is also safe. This is because the +Java compiler adds code to the start of a static method to make sure +the class is initialized. However, the C++ compiler does not +add this extra code. Hence, if you write a native static method +using CNI, you are responsible for calling @code{JvInitClass} +before doing anything else in the method (unless you are sure +it is safe to leave it out). + +Accessing a static field also requires the class of the +field to be initialized. The Java compiler will generate code +to call @code{Jv_InitClass} before getting or setting the field. +However, the C++ compiler will not generate this extra code, +so it is your responsibility to make sure the class is +initialized before you access a static field from C++. + + +@node Object allocation +@section Object allocation + +New Java objects are allocated using a +@dfn{class instance creation expression}, e.g.: + +@example +new @var{Type} ( ... ) +@end example + +The same syntax is used in C++. The main difference is that +C++ objects have to be explicitly deleted; in Java they are +automatically deleted by the garbage collector. +Using @acronym{CNI}, you can allocate a new Java object +using standard C++ syntax and the C++ compiler will allocate +memory from the garbage collector. If you have overloaded +constructors, the compiler will choose the correct one +using standard C++ overload resolution rules. + +@noindent For example: + +@example +java::util::Hashtable *ht = new java::util::Hashtable(120); +@end example + +@deftypefun void* _Jv_AllocBytes (jsize @var{size}) +Allocates @var{size} bytes from the heap. The memory is not scanned +by the garbage collector but it freed if no references to it are discovered. +@end deftypefun + + +@node Arrays +@section Arrays + +While in many ways Java is similar to C and C++, it is quite different +in its treatment of arrays. C arrays are based on the idea of pointer +arithmetic, which would be incompatible with Java's security +requirements. Java arrays are true objects (array types inherit from +@code{java.lang.Object}). An array-valued variable is one that +contains a reference (pointer) to an array object. + +Referencing a Java array in C++ code is done using the +@code{JArray} template, which as defined as follows: + +@example +class __JArray : public java::lang::Object +@{ +public: + int length; +@}; + +template +class JArray : public __JArray +@{ + T data[0]; +public: + T& operator[](jint i) @{ return data[i]; @} +@}; +@end example + + +There are a number of @code{typedef}s which correspond to @code{typedef}s +from the @acronym{JNI}. Each is the type of an array holding objects +of the relevant type: + +@example +typedef __JArray *jarray; +typedef JArray *jobjectArray; +typedef JArray *jbooleanArray; +typedef JArray *jbyteArray; +typedef JArray *jcharArray; +typedef JArray *jshortArray; +typedef JArray *jintArray; +typedef JArray *jlongArray; +typedef JArray *jfloatArray; +typedef JArray *jdoubleArray; +@end example + + +@deftypemethod {template} T* elements (JArray @var{array}) +This template function can be used to get a pointer to the elements of +the @code{array}. For instance, you can fetch a pointer to the +integers that make up an @code{int[]} like so: + +@example +extern jintArray foo; +jint *intp = elements (foo); +@end example + +The name of this function may change in the future. +@end deftypemethod + + +@deftypefun jobjectArray JvNewObjectArray (jsize @var{length}, jclass @var{klass}, jobject @var{init}) +Here @code{klass} is the type of elements of the array and +@code{init} is the initial value put into every slot in the array. +@end deftypefun + + +@subsection Creating arrays + +For each primitive type there is a function which can be used to +create a new array of that type. The name of the function is of the +form: + +@example +JvNew@var{Type}Array +@end example + +@noindent For example: + +@example +JvNewBooleanArray +@end example + +@noindent can be used to create an array of Java primitive boolean types. + +@noindent The following function definition is the template for all such functions: + +@deftypefun jbooleanArray JvNewBooleanArray (jint @var{length}) +Create's an array @var{length} indices long. +@end deftypefun + +@deftypefun jsize JvGetArrayLength (jarray @var{array}) +Returns the length of the @var{array}. +@end deftypefun + + +@node Methods +@section Methods + +Java methods are mapped directly into C++ methods. +The header files generated by @code{gcjh} +include the appropriate method definitions. +Basically, the generated methods have the same names and +@emph{corresponding} types as the Java methods, +and are called in the natural manner. + +@subsection Overloading + +Both Java and C++ provide method overloading, where multiple +methods in a class have the same name, and the correct one is chosen +(at compile time) depending on the argument types. +The rules for choosing the correct method are (as expected) more complicated +in C++ than in Java, but given a set of overloaded methods +generated by @code{gcjh} the C++ compiler will choose +the expected one. + +Common assemblers and linkers are not aware of C++ overloading, +so the standard implementation strategy is to encode the +parameter types of a method into its assembly-level name. +This encoding is called @dfn{mangling}, +and the encoded name is the @dfn{mangled name}. +The same mechanism is used to implement Java overloading. +For C++/Java interoperability, it is important that both the Java +and C++ compilers use the @emph{same} encoding scheme. + +@subsection Static methods + +Static Java methods are invoked in @acronym{CNI} using the standard +C++ syntax, using the @code{::} operator rather +than the @code{.} operator. + +@noindent For example: + +@example +jint i = java::lang::Math::round((jfloat) 2.3); +@end example + +@noindent C++ method definition syntax is used to define a static native method. +For example: + +@example +#include +java::lang::Integer* +java::lang::Integer::getInteger(jstring str) +@{ + ... +@} +@end example + + +@subsection Object Constructors + +Constructors are called implicitly as part of object allocation +using the @code{new} operator. + +@noindent For example: + +@example +java::lang::Integer *x = new java::lang::Integer(234); +@end example + +Java does not allow a constructor to be a native method. +This limitation can be coded round however because a constructor +can @emph{call} a native method. + + +@subsection Instance methods + +Calling a Java instance method from a C++ @acronym{CNI} method is done +using the standard C++ syntax, e.g.: + +@example +// @r{First create the Java object.} +java::lang::Integer *x = new java::lang::Integer(234); +// @r{Now call a method.} +jint prim_value = x->intValue(); +if (x->longValue == 0) + ... +@end example + +@noindent Defining a Java native instance method is also done the natural way: + +@example +#include + +jdouble +java::lang:Integer::doubleValue() +@{ + return (jdouble) value; +@} +@end example + + +@subsection Interface methods + +In Java you can call a method using an interface reference. This is +supported, but not completly. @xref{Interfaces}. + + + + +@node Strings +@section Strings + +@acronym{CNI} provides a number of utility functions for +working with Java Java @code{String} objects. +The names and interfaces are analogous to those of @acronym{JNI}. + + +@deftypefun jstring JvNewString (const char* @var{chars}, jsize @var{len}) +Returns a Java @code{String} object with characters from the C string +@var{chars} up to the index @var{len} in that array. +@end deftypefun + +@deftypefun jstring JvNewStringLatin1 (const char* @var{bytes}, jsize @var{len}) +Returns a Java @code{String} made up of @var{len} bytes from @var{bytes}. +@end deftypefun + + +@deftypefun jstring JvNewStringLatin1 (const char* @var{bytes}) +As above but the length of the @code{String} is @code{strlen(@var{bytes})}. +@end deftypefun + +@deftypefun jstring JvNewStringUTF (const char* @var{bytes}) +Returns a @code{String} which is made up of the UTF encoded characters +present in the C string @var{bytes}. +@end deftypefun + +@deftypefun jchar* JvGetStringChars (jstring @var{str}) +Returns a pointer to an array of characters making up the @code{String} @var{str}. +@end deftypefun + +@deftypefun int JvGetStringUTFLength (jstring @var{str}) +Returns the number of bytes required to encode the contents of the +@code{String} @var{str} in UTF-8. +@end deftypefun + +@deftypefun jsize JvGetStringUTFRegion (jstring @var{str}, jsize @var{start}, jsize @var{len}, char* @var{buf}) +Puts the UTF-8 encoding of a region of the @code{String} @var{str} into +the buffer @code{buf}. The region to fetch is marked by @var{start} and @var{len}. + +Note that @var{buf} is a buffer, not a C string. It is @emph{not} +null terminated. +@end deftypefun + + +@node Mixing with C++ +@section Interoperating with C/C++ + +Because @acronym{CNI} is designed to represent Java classes and methods it +cannot be mixed readily with C/C++ types. + +One important restriction is that Java classes cannot have non-Java +type instance or static variables and cannot have methods which take +non-Java types as arguments or return non-Java types. + +@noindent None of the following is possible with CNI: + +@example + +class ::MyClass : public java::lang::Object +@{ + char* variable; // @r{char* is not a valid Java type.} +@} + + +uint +::SomeClass::someMethod (char *arg) +@{ + . + . + . +@} // @r{@code{uint} is not a valid Java type, neither is @code{char*}} +@end example + +@noindent Of course, it is ok to use C/C++ types within the scope of a method: + + +@example +jint +::SomeClass::otherMethod (jstring str) +@{ + char *arg = ... + . + . + . +@} +@end example + +But this restriction can cause a problem so @acronym{CNI} includes the +@code{GcjRaw} class. The @code{GcjRaw} class is a @dfn{non-scanned reference} +type. In other words variables declared of type @code{GcjRaw} can +contain any data and are not checked by the compiler in any way. + +This means that you can put C/C++ data structures (including classes) +in your @acronym{CNI} classes, as long as you use the appropriate cast. + +@noindent Here are some examples: + +@example + +class ::MyClass : public java::lang::Object +@{ + GcjRaw string; + + MyClass (); + GcjRaw getText (); + void printText (); +@} + +::MyClass::MyClass () +@{ + char* text = ... + string = text; +@} + +GcjRaw +::MyClass::getText () +@{ + return string; +@} + +void +::MyClass::printText () +@{ + printf("%s\n", (char*) string); +@} +@end example + + +@node Exception Handling +@section Exception Handling + +While C++ and Java share a common exception handling framework, +things are not yet perfectly integrated. The main issue is that the +run-time type information facilities of the two +languages are not integrated. + +Still, things work fairly well. You can throw a Java exception from +C++ using the ordinary @code{throw} construct, and this +exception can be caught by Java code. Similarly, you can catch an +exception thrown from Java using the C++ @code{catch} +construct. + +@noindent Here is an example: + +@example +if (i >= count) + throw new java::lang::IndexOutOfBoundsException(); +@end example + +Normally, G++ will automatically detect when you are writing C++ +code that uses Java exceptions, and handle them appropriately. +However, if C++ code only needs to execute destructors when Java +exceptions are thrown through it, GCC will guess incorrectly. Sample +problematic code: + +@example +struct S @{ ~S(); @}; + +extern void bar(); // @r{Is implemented in Java and may throw exceptions.} + +void foo() +@{ + S s; + bar(); +@} +@end example + +The usual effect of an incorrect guess is a link failure, complaining of +a missing routine called @code{__gxx_personality_v0}. + +You can inform the compiler that Java exceptions are to be used in a +translation unit, irrespective of what it might think, by writing +@code{#pragma GCC java_exceptions} at the head of the +file. This @code{#pragma} must appear before any +functions that throw or catch exceptions, or run destructors when +exceptions are thrown through them. + +@node Synchronization +@section Synchronization + +Each Java object has an implicit monitor. +The Java VM uses the instruction @code{monitorenter} to acquire +and lock a monitor, and @code{monitorexit} to release it. + +The corresponding CNI macros are @code{JvMonitorEnter} and +@code{JvMonitorExit} (JNI has similar methods @code{MonitorEnter} +and @code{MonitorExit}). + + +The Java source language does not provide direct access to these primitives. +Instead, there is a @code{synchronized} statement that does an +implicit @code{monitorenter} before entry to the block, +and does a @code{monitorexit} on exit from the block. +Note that the lock has to be released even when the block is abnormally +terminated by an exception, which means there is an implicit +@code{try finally} surrounding synchronization locks. + +From C++, it makes sense to use a destructor to release a lock. +@acronym{CNI} defines the following utility class: + +@example +class JvSynchronize() @{ + jobject obj; + JvSynchronize(jobject o) @{ obj = o; JvMonitorEnter(o); @} + ~JvSynchronize() @{ JvMonitorExit(obj); @} +@}; +@end example + +So this Java code: + +@example +synchronized (OBJ) +@{ + CODE +@} +@end example + +@noindent might become this C++ code: + +@example +@{ + JvSynchronize dummy (OBJ); + CODE; +@} +@end example + +Java also has methods with the @code{synchronized} attribute. +This is equivalent to wrapping the entire method body in a +@code{synchronized} statement. +(Alternatively, an implementation could require the caller to do +the synchronization. This is not practical for a compiler, because +each virtual method call would have to test at run-time if +synchronization is needed.) Since in @code{gcj} +the @code{synchronized} attribute is handled by the +method implementation, it is up to the programmer +of a synchronized native method to handle the synchronization +(in the C++ implementation of the method). +In otherwords, you need to manually add @code{JvSynchronize} +in a @code{native synchornized} method. + + +@node Reflection +@section Reflection + +Reflection is possible with CNI code, it functions similarly to how it +functions with JNI@. + +@c clean this up... I mean, what are the types jfieldID and jmethodID in JNI? +The types @code{jfieldID} and @code{jmethodID} +are as in JNI@. + +@noindent The functions: + +@itemize +@item @code{JvFromReflectedField}, +@item @code{JvFromReflectedMethod}, +@item @code{JvToReflectedField} +@item @code{JvToFromReflectedMethod} +@end itemize + +@noindent will be added shortly, as will other functions corresponding to JNI@. + + + @node Resources @chapter Resources