Invocation API: JFrame opens and closes immediatly when invoced.

Question

Hello,
I'm sitting with an existing software, to which I would like to create a Java GUI to present calculation results in a nice way (simple editing, saving in different formats, etc.). The core is Fortran 77 and 90.
Right now I'm trying to figure out how JNI works, and I have been able to make some C code show a Jframe. However, the JFrame disappears immediately if I don't make the runningThread.sleep() for some time, and I can't seem to find any GUI sample code. If I run it in NetBeans it stays open until I click the X.
In the end I would like the GUI to be started from Fortran 90 when a user gives the plot command in the application console.
In addition to the above problem, I would like a push in the right direction. What should I think about with this approach? Any common traps?
This is how the test looks:
Java code generated by NetBeans, where I just want to display a JFrame.
public class JFrame extends javax.swing.JFrame {
    public JFrame() {
        initComponents();
    @SuppressWarnings("unchecked")
    private void initComponents() {
        setDefaultCloseOperation(javax.swing.WindowConstants.DISPOSE_ON_CLOSE);
        setTitle("JFrameInvoced");
        setCursor(new java.awt.Cursor(java.awt.Cursor.DEFAULT_CURSOR));
        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 400, Short.MAX_VALUE)
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 300, Short.MAX_VALUE)
        pack();
    @SuppressWarnings("static-access")
    public static void main(String args[]) throws InterruptedException {
        JFrame frameTest = new JFrame();
        frameTest.setVisible(true);
        Thread runningNow = Thread.currentThread();
        runningNow.sleep(1000);
}C code from internet.
#include <stdio.h>
#include <jni.h>
JNIEnv* create_vm() {
     JavaVM* jvm;
     JNIEnv* env;
     JavaVMInitArgs args;
     JavaVMOption options[1];
     int ret;
     /* There is a new JNI_VERSION_1_4, but it doesn't add anything for the purposes of our example. */
     args.version = JNI_VERSION_1_4;
     args.nOptions = 1;
     options[0].optionString = "-Djava.class.path=D:\\Source\\Invocation_test";
     args.options = options;
     args.ignoreUnrecognized = JNI_FALSE;
     ret = JNI_CreateJavaVM(&jvm, (void **)&env, &args);
     return env;
void invoke_class(JNIEnv* env) {
     jclass helloWorldClass;
     jmethodID mainMethod;
     jobjectArray applicationArgs;
     jstring applicationArg0;
     //helloWorldClass = (*env)->FindClass(env, "InvocationHelloWorld");
     helloWorldClass = (*env)->FindClass(env, "JFrame");
     mainMethod = (*env)->GetStaticMethodID(env, helloWorldClass, "main", "([Ljava/lang/String;)V");
     applicationArgs = (*env)->NewObjectArray(env, 1, (*env)->FindClass(env, "java/lang/String"), NULL);
     applicationArg0 = (*env)->NewStringUTF(env, "From-C-program");
     (*env)->SetObjectArrayElement(env, applicationArgs, 0, applicationArg0);
     (*env)->CallStaticVoidMethod(env, helloWorldClass, mainMethod, applicationArgs);
int main(int argc, char **argv) {
     JNIEnv* env = create_vm();
     invoke_class( env );
}

Answer 1

sammen wrote:
Can multithreading be a possible solution to this?Multithreading is certainly involved when you create a GUI using SWING, as SWING automatically creates a thread where all drawing and event handling is performed. Calculations and other longer tasks are performed outside that thread. This is done to avoid blocking the GUI during calculations.
But first focus on the interface between the C program, where the calculations are performed, and the Java program, where the GUI should be located. Possible questions you should ask yourself are:
- What data must be sent from the C part to the GUI?
- What actions do I want to trigger from the C part, e.g. "create a plot"?
- What actions do I want to trigger from the GUI to the C part, e.g. "redo calculations"?
Then you could design the interface between those two. The multithreading performed by SWING has to be considered especially for the third question, as event handlers like "actionPerformed" are called from the SWING thread and should return quickly, just triggering the action, but not performing it. But those things are better discussed in the SWING forum.
Martin