//---------------------------------------------------------------------------
 
TForm *getForm(JNIEnv *env, jobject obj)
{
    jfieldID HandleField= env->GetFieldID(env->GetObjectClass(obj), "nativeHandle", "J");
    jlong handle = env->GetLongField(obj, HandleField);
    return reinterpret_cast<TForm *>(handle);
}
//---------------------------------------------------------------------------
 
jlong JNICALL Java_my_TestJNIForm_initialise(JNIEnv *, jobject)
{
    TForm *form=new TForm(Application);
    form->Caption="1";
    return (jlong)form;
}
//---------------------------------------------------------------------------
 
void JNICALL Java_my_TestJNIForm_show(JNIEnv *env, jobject obj)
{
    TForm *form = getForm(env, obj);
    form->Show();
}
//---------------------------------------------------------------------------
 
jint JNICALL Java_my_TestJNIForm_getVal(JNIEnv *env, jobject obj)
{
    TForm *form = getForm(env, obj);
    return StrToInt(form->Caption);
}
//---------------------------------------------------------------------------
 
void JNICALL Java_my_TestJNIForm_setVal(JNIEnv *env, jobject obj, jint val)
{
    TForm *form = getForm(env, obj);
    form->Caption=IntToStr(val);
}
//---------------------------------------------------------------------------

new Thread(new Runnable() {
                    @Override
                    public void run() {
                        setVal(7);
                        show();
                    }
                }).start();

package my;

import javax.swing.JFrame;

public class TestJNIForm {

    public TestJNIForm() {

        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);

        showVCLForm();
    }

    public static void main(String[] args) {
        new TestJNIForm();
    }

    static {
        System.loadLibrary("JNIForm");
    }

    private native void showVCLForm();
}

//---------------------------------------------------------------------------

void JNICALL Java_my_TestJNIForm_showVCLForm(JNIEnv *, jobject)
{
    TForm *form=new TForm(Application);
    form->Show();
}
//---------------------------------------------------------------------------