Can a derived class catch base class object

can a derived class object catch a base class object
e-g if i have a class
class Test {
// code
}and
class Test2 extends Test {
}and lets say there is a method that return an object of Test (base class), so is it possible to write
Test2 t=getTestObj(); // i-e subclass holding base class objectif its not.. how can we do so? so that derived class should hold base class object....

sorry..
here is how it goes
i have a function a class
public Test getObj() {
// code
}The constraint is that i cant change the implementation of this above function.
Now when i call this function, it returns me a Test object. But i cant do
Test t=getObj();because the Test class is written purely in java whereas i want to use write a new Test class that implements the same functionality [using the above given function] in JNI.
so what i did, i created a new package [nativ] and created a class "Test" in that. But since i have to use the function that returns me Test and not "nativ.Test", so what i did, i inherited nativ.Test from "Test" so that the object might resolve the reference.
So this is it.. that i cant modify the function and i need some way to do it.. plz reply

Similar Messages

Casting base class object to derived class object

interface myinterface
     void fun1();
class Base implements myinterface
     public void fun1()
class Derived extends Base
public class File1
     public myinterface fun()
          return (myinterface) new Base();
     public static void main(String args[])
          File1 obj = new File1();
          Derived dobj = (Derived)obj.fun();
Giving the exception ClassCastException......
Can't we convert from base class object to derived class.
Can any one help me please...
Thnaks in Advance
Bharath kumar.

When posting code, please use tags
The object returned by File1.fun() is of type Base. You cannot cast an object to something it isn't - in this case, Base isn't Dervied. If you added some member variables to Derived, and the compiler allowed your cast from Base to Derived to succeed, where would these member variables come from?
Also, you don't need the cast to myinterface in File1.fun()
Also, normal Java coding conventions recommend naming classes and interfaces (in this case, myinterface) with leading capital letters, and camel-case caps throughout (e.g. MyInterface)

Why cannnot derived class pointer point to a base class object?

Hi,
Pleaseeee... explain me why cannot the derived class pointer point to a base class object.
I know that Base class pointer can point to a derived class object.
Thanks & Regards,
Vig....

Example:
class Base
{ public: void foo(); } * pBase;
class Derived : public Base
{ public: void bar(); } * pDerived;
Now, what would happen if you assign pDerived = new Base() and then call pDerived->bar()?By forbidding such an assignment, compiler prevents you from writing error-prone code.

Pass Class Object To FMS Using NetConnection.call Method

Hello All,
I have a custom class that defines several methods on itself
to retrieve its data. This class object is then sent to FMS via the
NetConnection.call method. Once received by FMS, FMS calls the
remote method to dispaly the class object on connected clients
(minus the originator).
Now, standard properties are displayed correctly, but when I
call the class method to retrieve the class data, no data is
retrieved.
My question is, can FMS handle class objects as parameters in
a NetConnection call. If not, is there a better practice of
applying methods to retrieve the class data? Example below...
class com.QuizItem
var numOfAnswers;
var getAnswer;
function QuizItem(question)
this.numOfAnswers = 0;//<-- Returns correct number of
answers
this.getAnswer = function(answerNumberToGet)//<-- Does
not return any data when called by client side script
return this.answers[answerNumberToGet];//Already populated
array
Regards,
Shack

First, I know JAVA does not working "pass by
reference". It's only working pass by value. (or call
by value)But obviously you don't fully understand what it means.
Isn't main_a and method_a alias?
if there is not alias, why? please explain to me.No. They're two independent references coincidentally pointing to the same object. In your swap method, you move method_a to point to something else. This does not affect main_a.
and why main_a.hashcode() is main_a's value?why not? What else should it be?
I think It's mean copy object. but main_a and
method_a, they have same object id! @_@;;;It means "copy reference", same object.

How to call a Derived call fucntion with a base class object ?

Hi all
i am working on a JNI interface to Java, and in the process of simulating a C++ behaviour in java
so i need some help form you people, in this regard.
here is a c++ code, i need a equivalent fucntionality in java , to put it one word, the question is
how to implement the dynamic_cast functionality in java, as java also has virtual fucntions, i think
this should be possible, if it is not, what is the alternative
class Base
public:
     Base()
     ~Base()
     virtual void F1()
          cout<<"The BASE::F1() is called"<<endl;
     virtual void F2()
          cout<<"The BASE::F2() is called"<<endl;
class Derived : public Base
public:
     Derived()
     ~Derived()
     virtual void F3()
          cout<<"The Derived::F3() is called"<<endl;
     virtual void F4()
          cout<<"The Derived::F4() is called"<<endl;
Base * GetDerived()
     return new Derived();
int _tmain(int argc, _TCHAR* argv[])
     Base *ptr = NULL;
                ptr = GetDerived();
     Derived *dPtr = dynamic_cast<Derived *>(ptr);
                dPtr->F3();
}regards
pradish

Just to clarify a point that I consider important--the distinction between references and objects:
Your subject is: How to call a Derived call fucntion with a base class object ? The answer to that is: You cannot. It is completely impossible in Java. If you have a base class object, the derivced class' methods are not present. On the other hand, if you have a compile-time reference of the parent type, but at runtime it happens to point to an instance of the derived class, then, as pointed out, you can cast the reference. (Note that casting does not apply to objects.)

Set fields of derived class in base class constructor via reflection?

Does the Java Language Specification explicitly allow setting of fields of a derived class from within the base class' constructor via reflection? The following test case runs green, but I would really like to know if this Java code is compatible among different VM implementations.
Many thanks for your feedback!
Norman
public class DerivedClassReflectionWorksInBaseClassConstructorTest extends TestCase {
abstract static class A {
    A() {
        try {
            getClass().getDeclaredField("x").setInt(this, 42);
        } catch (Exception e) {
            throw new RuntimeException(e);
static class B extends A {
    int x;
    B() {
    B(int x) {
        this.x = x;
public void testThatItWorks() {
    assertEquals(42, new B().x);
    assertEquals(99, new B(99).x);
}

why not just put a method in the superclass that the subclasses can call to initialize the subclass member variable?In derived classes (which are plug-ins), clients can use a field annotation which provides some parameter metadata such as validators and the default value. The framework must set the default value of fields, before the class' initializer or constructors are called. If the framework would do this after derived class' initializer or constructors are called, they would be overwritten:
Framework:
public abstract class Operator {
    public abstract void initialize();
}Plug-In:
public class SomeOperator extends Operator {
    @Parameter(defaultValue="42", interval="[0,100)")
    double threshold;
    @Parameter(defaultValue="C", valueSet="A,B,C")
    String mode;
    public void setThreshold(double threshold) {this.threshold = threshold;}
    public void setMode(String mode) {this.mode = mode;}
    // called by the framework after default values have been set
    public void initialize() {
}On the other hand, the default values and other metadata are also used to create GUIs and XML I/O for the derived operator class, without having it instantiated. So we cannot use the initial instance field values for that, because we don't have an instance.

Base class vs derived class

We have entity classes that we use to access our database. We have subclasses derived from these entity classes that apply business rules. For instance, the base class AddressEntity has a
setAddress2(string) that AddressEntity.select() uses to set a class variable with data retrieved from the database. The derived class Address also has a setAddress2(string) method that puts restrictions on the length of the data. I want the AddressEntity.select() method to use the base class method AddressEntity.setAddress2(). I've tried using this.setAddress2() in AddressEntity.select() but the derived class method is still used. Any suggestions?
Thanks,
Joe

If you need to call some methods on the base class sometimes and some methods on the derived class other times, but using the same object, then yes dubwai is right you should revisit your Object hierarchy.
One simple way to do what you are asking is to have your method(s) look like this:
void setAddress2(String sAddress) { setAddress2(sAddress, true); }
void setAddress2(String sAddress, boolean bRestrictLength) {
// real method
}then you could just look at the variable bRestrictLength to see if you need to restrict the length, and have it default to true. In this way you can use overloading to solve your problem.

Base class/Derived class

Hi all,
I have
class Base {
int a;
class Derived{
int b;
now if i do
Base X = new Base();
Derived D = new Derived();
It Doesn't allow me to do D=X
But it does allow me to do X=D.
whats the reason behind it. And what actually happens when i do X=D , does the copy constructor gets called ?
Thanx

Manthana wrote:
Hi, u said
the value of X becomes the reference to the instance of Derived that you created when you called "new Derived()".
So now i can access attributes of derived class from the reference X right X.b
But i cant do X.b
Why?Please spell out words like "you". It makes things easier to read. :)
With Derived extending Base, you could say:
X = D;
X.a = 5;Because the compiler and runtime see X as a reference to a Base object, you can only access variables/methods defined in Base. Since X is declared as being a reference to Base, you always know that 'a' is defined. 'b' wouldn't be defined for X if you said:
X = new Base();
X.b = 52;So, in order to access the b, you'd have to access it with something declared as a reference to Derived, such as 'D':
D.b = 10;You could say:
X = D; // Line 1
Derived d2 = (Derived)X;
d2.b = 10;But, then you'll get a ClassCastException if X is only referring to a Base object [e.g., if Line 1 was "X = new Base();"], not to a Derived object.

Can I work with a derived class from u0093ApplicationClassu0094

Hello, I want to create a derived class from ApplicationClass for use in my Application, the problem is the function SAPbouiCOM.SboGuiApi.GetApplication(-1), it return a COM object. If I do a specific cast to my own class (that derive from ApplicationClass), the metod give a COM exception and say that I cant do a specific cast with a COM object.
Can I do that cast? And How can I do it?
Im programming in C#.
Thanks.

I think that you can´t assign an object of the base class
to an object of the derived class. I don´t know why you need to do that. With more information we could help you

Flex/AS3 Best way to construct a derived class instance from an existing base class instance?

What is the best way to handle the instantiation of a derived class from an existing base class.
I have a base class which is being created via remote_object [RemoteClass alias] from the server.   I have other specialized classes that are derived from this baseclass, but serialization with the server always happens with the base class.     The base class has meta data that defines what the derived class is, for example
[RemoteClass (alias="com.myco...')]
public Class Base
     public var derivedType:String;
     public function Base()
public Class Derived extends Base
     public "some other data"
     public function Derived()
In my Cairgorm command which retrieves this object from ther server I want to do this:
public function result (event: Object):void
    var baseInstance:Base = event.result;
     if (baseInstance.derivedType = "derived")
          var derivedInstance:Derived = new Derived( baseInstance );
What is the most efficient way of doing this?   It appears to me that doing a deep-copy/clone and instantiation of the derived class is pretty inefficient as far as memory allocation and data movement via the copy.

Thanks for the assistance. Let me try to clarify.
MY UI requires a number of composite classes.    The individual components of the composite classes are being transfered to/from the server at different times depending upone which component has changed state.    The construction of the composite classes from the base class happens in my clients business logic.
Composition happens in a derived class; but server syncronization happens using the base class.    When I recieve the object from Blazeds through the remote object event, it is in the form of the base class. I then need to instantiate the derived class and copy the elements of the base class into it (for later composite construction).   And likewise when sending the base class back to the server, I need to upcast the derived class to its base class.   But in this case just a mere upcast does not work. I actually need to create a new base class and copy the attrbutes into it. I believe this is limitation of how remoting works on Flex/AS3.
My question is, what is the best way to turn my base class into it's derived class so further composite construction can take place.   The way I am currently doing it is to create a load method on the base class, that takes the base class as on argument. The load function, copies all of the instance attribute references from the base class to the target class.
public Class Base
     public function Base()
     public function load(fromClass:Base)
    { // copy the references for all of the instance attributes from the fromClass to this class }
Then, after I recieve the base class from the server.   I create a new derived class and pass the base class into the load function like this:
            for (var i:int=0; i < event.result.length; i++) {
                var derived:Derived = new Derived();
                derived.load(event.result[i]);
The drawbacks of this approach is that it now requires 2 extra instance creations per object serialization.   One on recieving the object from the server and one sending it to the server.    I assume copying references are pretty efficient. But, there is probably some GC issues.     The worst of it is in code maintenance.   The load function now has to be manually maintained and kept in sync with the server class.
It would be interesting to hear how others have solved this problem.      The server side is an existing application with around 2M LOC, so changing the code on the server is a non-starter.
Thanks for your help.

Managing constants in base / derived classes

Hi there,
The problem:
I'm facing what is certainly a simple problem but fail to come up with an acceptable solution. What I'd like to do is managing constants in a base class and derived class... which for some reasons are not parts of the same package. Also, these constants may have different values in the derived base.
Down to earth description:
Class base uses a set of constants A=1, B=2, C=3.
Class derived should be provided with similarly named constants but they may have different values A=10, B=20, C=30. I could declared these constants in the classes themselves but somehow I think this is ugly.
A "solution" that does not work:
Assume for a moment that I'm just a very naive programmer (which actually I am... but anyway...). I would them come up with something like:
package base;
import base.Constants;
public class Base {
    public Base() {
    public void myfunction() {
       System.out.println("My constant: " + Constants.A);
}and
package derived;
import derived.Constants;
public class Derived extends Base {
    public Derived() {
}Now of course this is stupid since Derived.myfunction() prints the value of the constants given by Base.myfunction()The question is: is there a static construction that would allow me to have the desired behaviour? What I mean is that I don't want to provide a "Constants" object nor an hashtable dynamically loaded or whatever.
Bonus question:
I'm not a pro in OOP (seriously guys... C rocks! Oops, wrong forum :-) but it seems to be a case of "code inheritance" vs "behaviour inheritance" (I just made those expressions up!). What I mean is: if what is inherited is the actual "code" of the methods (as if a huge copy paste took place) then the naive solution would work. But in the real world, a "behaviour inheritance" is at work in the sense that what is inherited is the "behaviour" (or, more bluntly, simply the code as compiled in the base class). Hmm... Am I making any sense here? Is that distinction theorized in some way? I tried to search a bit by myself but did not know where to start.
Thanks,

I mucked around with this exact problem a while back.
The (simplified) scenario is AbstractCourse is extended by CookingCourse, WritingCourse, and BusinessCourse. Every course has a basePrice and a materialsCost... both of which vary from course to course... The same price calculation applies to all types of course, just the amounts will vary.
totalPrice = basePrice + materialsCost The traditional non-oo solution is simple enough... you would just create a "table" of all six contstants, and a function with a switch statement...
but How to do this "The OO Way"?
What I came up with is:
class BaseCourse {
abstract double getBasePrice();
abstract double getMaterialsCost();
public double getPrice() {
    return getBasePrice() + getMaterialsCost();
public class CookingCourse {
private static final double BASE_PRICE = 300.00;
private static final double MATERIALS_COST = 112.60;
public double getBasePrice() { return CookingCourse.BASE_PRICE }
public double getMaterialsCost() { return CookingCourse.MATERIALS_COST }
public class WritingCourse {
private static final double BASE_PRICE = 200.00;
private static final double MATERIALS_COST = 50.00;
public double getBasePrice() { return WritingCourse.BASE_PRICE }
public double getMaterialsCost() { return WritingCourse.MATERIALS_COST }
public class BusinessCourse {
private static final double BASE_PRICE = 600.00;
private static final double MATERIALS_COST = 18.12;
public double getBasePrice() { return BusinessCourse.BASE_PRICE }
public double getMaterialsCost() { return BusinessCourse.MATERIALS_COST }
}The base class specifies that each subclass must be able to tell it's base price, and it's materials cost... then we implement the calculation on those values just once, in the base class.
For all I know there are much more succinct, flexible, efficient, and basically much more smarter ways of doing this... this is just a way that worked for me... and it's simple enough so even I can follow it.
Java can be a very very very very verbose language :-( ... But hey it still shits on C ;-)
Cheers. Keith.
Edited by: corlettk on 23/05/2008 11:17 - typos

Can't find class because of try catch block ?!

Hello,
I'm using the JNI to use a java library from my c++ code.
JNI can't find the "Comverse10" class below, but when i put the try catch block in createMessage in comment, FindClass succeeds ?!
Unfortunatly i need the code inside the try block ;-)
I tried a few things, but none of them worked:
- let createMessage throw the exception (public void createMessage throws ElementAlreadyExistsException ), so there isn't a try catch block in createMessage => result: the same
- make a "wrapper" class Comverse that has a Comverse10 object as attribute and just calls the corresponding Comverse10.function. Result: Comvers could be found, but not constructed (NewObject failed).
Can someone tell me what is going on ?!
Thank you,
Pieter.
//Comverse10 class
public class Comverse10 {
MultimediaMessage message;
/** Creates a new instance of Comverse10 */
public Comverse10() {
public void createMessage() {
TextMediaElement text1 = new TextMediaElement("Pieter");
text1.setColor(Color.blue);
SimpleSlide slide1 = new SimpleSlide();
//if i put this try catch block in comment, it works ?!
try{
slide1.add(text1);
catch(com.comverse.mms.mmspade.api.ElementAlreadyExistsException e){}
MessageContent content = new MessageContent();
content.addSlide(slide1);
this.message = new MultimediaMessage();
message.setContent(content);
message.setSubject("Mijn subjectje");
for those of you who are intersted: here's my C++ code:
//creation of JVM
HRESULT Java::CreateJavaVMdll()
     HRESULT HRv = S_OK;
char classpath[1024];
     jint res;
     if(blog)     this->oDebugLog->Printf("CreateJavaVMdll()");
     strcpy(classpath,"-Djava.class.path="); /*This tells jvm that it is getting the class path*/
     strcat(classpath,getenv("PATH"));
     strcat(classpath,";D:\\Projects\\RingRing\\MMSComposer;C:\\Progra~1\\j2sdk1~1.1_0\\lib");     //;C:\\Comverse\\MMS_SDK\\SDK\\lib\\mail.jar;C:\\Comverse\\MMS_SDK\\SDK\\lib\\activation.jar;C:\\Comverse\\MMS_SDK\\SDK\\lib\\mmspade.jar
     //------Set Options for virtual machine
     options[0].optionString = "-Djava.compiler=NONE"; //JIT compiler
     options[1].optionString = classpath;                                        //CLASSPATH
     //------Set argument structure components
     vm_args.options = options;
     vm_args.nOptions = 2;
     vm_args.ignoreUnrecognized = JNI_TRUE;
     vm_args.version = JNI_VERSION_1_4;
     /* Win32 version */
     HINSTANCE hVM = LoadLibrary("C:\\Program Files\\j2sdk1.4.1_01\\jre\\bin\\client\\jvm.dll");
     if (hVM == NULL){
          if(blog) oDebugLog->Printf("Can't load jvm.dll");
          return E_FAIL;
     if(blog) oDebugLog->Printf("jvm.dll loaded\n");
     LPFNDLLFUNC1 func = (LPFNDLLFUNC1)GetProcAddress(hVM, "JNI_CreateJavaVM");
     if(!func){
          if(blog)     oDebugLog->Printf("Can't get ProcAddress of JNI_CreateJavaVM");
          FreeLibrary(hVM);     hVM = NULL;
          return E_FAIL;
     if(blog)     oDebugLog->Printf("ProcAddress found");
     res = func(&jvm,(void**)&env,&vm_args);
     if (res < 0) {
if(blog)     oDebugLog->Printf("Can't create JVM with JNI_CreateJavaVM %d\n",res);
return E_FAIL;
     if(blog)     oDebugLog->Printf("JVM created");
     return HRv;
//finding Comverse10 class:
HRESULT CALLAS MMSComposer::InitializeJNI(void)
     HRESULT HRv=E_FAIL;
     DWORD T=0;
     try
          if(blog)     oDebugLog->Printf("\nInitializeJNI()");
          bJVM = FALSE;
          jni = new Java(oDebugLog);
          if(jni->CreateJavaVMdll()!=S_OK){
               if(blog)     oDebugLog->Printf("CreateJavaVMdll() failed");
               return HRv;
          jclass jcls = jni->env->FindClass("Comverse10");
          if (jcls == 0) {
if(blog)     oDebugLog->Printf("Can't find Comverse10 class");
               jclass jcls2 = jni->env->FindClass("test");
               if (jcls2 == 0) {
                    if(blog)     oDebugLog->Printf("Can't find test class");
                    return HRv;
               if(blog)     oDebugLog->Printf("test class found %08x",jcls2);
return HRv;
          if(blog)     oDebugLog->Printf("Comverse10 class found %08x",jcls);
          jmethodID mid = jni->env->GetMethodID(jcls , "<init>", "()V");
          if (mid == 0) {
               if(blog)     oDebugLog->Printf("Can't find Comverse10() constructor");
return HRv;
          if(blog)     oDebugLog->Printf("Comverse10() constructor found");
          jobject jobj = jni->env->NewObject(jcls,mid);
          if(jobj==0)
               if(blog)     oDebugLog->Printf("Can't construct a Comverse10 object");
return HRv;
          if(blog)     oDebugLog->Printf("Comverse10 object constucted");
          //Create Global reference, so java garbage collector won't delete it
          jni->jobj_comv = jni->env->NewGlobalRef(jobj);
          if(jni->jobj_comv==0)
               if(blog)     oDebugLog->Printf("Can't create global reference to Comverse10 object");
return HRv;
          if(blog)     oDebugLog->Printf("global reference to Comverse10 object %08x created",jni->jobj_comv);
          bJVM=TRUE;
          HRv=S_OK;
     }     catch( IDB * bgError ) { throw bgError->ErrorTrace("InitializeJNI::~InitializeJNI",HRv, 0, T); }
          catch(...) { throw IDB::NewErrorTrace("InitializeJNI::~InitializeJNI",HRv, 0, T ); }
          return HRv;

>
I would guess that the real problem is that that the
exception you are catching is not in the class path
that you are defining.Thanks jschell, that was indeed the case.
I don't have the docs, but I would guess that
FindClass() only returns null if an exception is
thrown. And you are not checking for the exception.
Which would tell you the problem.Ok, i'll remember that. But what with exceptions thrown in my java code, the documents say
// jthrowable ExceptionOccurred(JNIEnv *env);
// Determines if an exception is being thrown. The exception stays being thrown until either the native code calls ExceptionClear(), or the Java code handles the exception
so, what if the java code throws an exception and catches it, will i be able to see that in my c++ code with ExceptionOccurred ?
or
should the java method be declared to throw the exception (and not catch it inside the method)
Again, thank you for your help, it's greatly appreciated !

Can i call non -abstract method in abstract class into a derived class?

Hi all,
Is it possible in java to call a non-abstract method in a abstact class from a class derived from it or this is not possible in java.
The following example will explain this Ques. in detail.
abstract class A
void amethod()
System.out.println(" I am in Base Class");
public class B extends A
void amethod()
System.out.println(" I am in Derived Class");
public static void main (String args[])
// How i code this part to call a method amathod() which will print "I am in Base Class
}

Ok, if you want to call a non-static method from a
static method, then you have to provide an object. In
this case it does not matter whether the method is in
an abstract base class or whatever. You simply cannot
(in any object oriented language, including C++ and
JAVA) call a nonstatic method without providing an
object, on which you will call the method.
To my solution with reflection: It also only works,
if you have an object. And: if you use
getDeclaredMethod, then invoke should not call B's
method, but A's. if you would use getMethod, then the
Method object returned would reflect to B's method.
The process of resolving overloaded methods is
performed during the getMethod call, not during the
invoke (at least AFAIK, please tell me, if I'm wrong).You are wrong....
class A {
    public void dummy() {
         System.out.println("Dymmy in A");
class B extends A {
     public void dummy() {
          System.out.println("Dymmy in B");
     public static void main(String[] args) throws Exception {
          A tmp = new B();
          Class clazz = A.class;
          Method method = clazz.getDeclaredMethod("dummy", null);
          method.invoke(tmp, null);
}Prints:
Dymmy in B
/Kaj

Warning :: Derived class hides the base class virtual function

We are porting from CC5.3 to CC5.8 compiler with Sun Studio one compiler. After plenty of hurdles we are in the final stage of removing the warning messages... Amoung the plenty the following one is very common and in different files. Why am I getting this error in 5.8 and not in 5.3 compiler....
Warning: derived_Object::markRead Hides the virtual function base_Object::markRead(ut_SourceCodeLocation&) const in a virtual base
From this it is easily understandable that the base class mark read was hidden by derived class markRead... when we drive and override the derived class function.... It is all over the place....
Thank you,
Saravanan Kannan
//public: using xx_Object :: markRead;
virtual void markRead() const;

The Sun C++ FAQ discusses the warning message:
http://developers.sun.com/prodtech/cc/documentation/ss11/mr/READMEs/c++_faq.html#Coding1
Notice that warnings are not necessarily errors. But I applaud your desire to fix the code so that it generates no warnings. I wish more of our customers could be persuaded to do the same. :-)
C++ 5.3 issues this warning, by the way. Example:
struct B { virtual int foo(int); };
struct D : B { virtual int foo(double); }; // line 2
D d;
line 2: Warning: D::foo hides the virtual function B::foo(int).
If for your particular code you do not see a warning with C++ 5.3, it would be due to a bug in C++ 5.3 that was later fixed.

How can I convert a string to an object or class

I would like to read a file representing a class, and convert it to an object or a class (object preferred). Other postings suggest using javax.tools.JavaCompiler to convert from a string but then say that this is not always available (posting on 1 Jan 09). If this is still not universally available is there another way to do this? If this is not available, are there any examples of how it should be done?
My understanding from what I've read is to read the file into a String then compile the String using javax.tools.JavaCompiler, which is an Interface.
thanks

skidmarks wrote:
What i would like to do is to take a Java file representing a class and compile it at runtime. However, the comment about a JDK being available at runtime makes this unattractive.So, you want to compile .java files, but you don't want to have to use a compiler?
The next guess would to be to create a .jar file and reference it at runtime. Here's the scenario:Eh? How is that even remotely equivalent?
1. People using the 'system' will have a varied knowledge of Java.
2. My hope was to require that anyone using the program would only need to create a Java Class file,You mean a Java source file. You have said that YOU want to create the .class file. If they are creating the .class file, then all you need to do is load it with a ClassLoader and start using it.
You might try clarifying your requirements a bit.
In either case, the Class Files would look like:
public class Name {
int field1;
float field2;
} With all the field types being simple Java Primitives.What is the point of this? What are you ultimately trying to accomplish, that can be served by user-defined groups of primitives, with no complex object graphs and no user-defined methods?
Depending on what you're really getting at, using scripting features via beanshell, groovy, or javascript might be an approach to consider, or using Scala to produce a domain-specific language (although I suspect that last may be overkill, and beyond your current skill level).
If this is so, is there any way to create a .jar file at runtime? Do I have to exec("jar") or is there another way.A .jar file is just a .zip file with a manifest. Look at the java.util.jar package. But note that creating a .jar file has nothing to do with the rest of what you're asking about.

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