CODEWITHSUNDEEP
javaclassvisual-c++structurejna
Mahantesh M Ambi
Mahantesh M Ambi

Reputation: 796

What is the purpose of getFieldOrder() in structure class?

I am trying to call a C++ function present within a .dll file. The C++ function takes structure object as parameter by reference,and function will assign values in that function.

In my Java application, in order to pass a structure object to a function, I wrote this:

interface someinterface extends Library{
 public static  class strctclass extends Structure
{
    public static  class ByReference extends tTIDFUDeviceInfo implements Structure.ByReference {}
    public short xxx=0;
    public char yyy='0';
    public boolean zzz=false
    public String www=new String();
    protected ArrayList getFieldOrder() {
        // TODO Auto-generated method stub
        ArrayList fields = new ArrayList();
    fields.add(Arrays.asList(new short{xxx}));
    fields.add(Arrays.asList(new char{yyy}));
    fields.add(Arrays.asList(new boolean{zzz}));
    fields.add(Arrays.asList(new String{www}));
    return fields;
}
someinterface instance=(someinterface) Native.loadLibrary("mydll", someinterface.class);
int somefunction(strctclass.ByReference strobject);
}

my main class:

public class Someclass
{
 public static void main(String args[])
{
 someinterface.strctclass.ByReference sss=new someinterface.strctclass.ByReference();
 someinterface obj=someinterface.instance;
 obj.somefunction(sss);
}
}

When I tried this, it is giving me this error:

java.lang.ClassCastException: java.util.Arrays$ArrayList cannot be cast to java.lang.Comparable

What do I do? Is there a problem in the getFieldOrder() function?

How exactly will JNA convert the class object in java to structure object in C++?

The exception is happening when I call the function.

Upvotes: 6

Views: 8298

Answers (1)

technomage
technomage

Reputation: 10069

From the JavaDoc:

Return this Structure's field names in their proper order

However, you are going to quickly run up against the fact that you're attempting to map a JNA Structure onto a C++ class, which simply won't work. JNA does not provide any automatic translation between JNA and C++ classes.

To be explicit:

protected List<String> getFieldOrder() {
    return Arrays.asList(new String[] { "xxx", "yyy", "zzz", "www" });
}

Upvotes: 1

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