java - 在一个方法调用仍在进行时调用第二个方法会导致程序崩溃

Question

我的程序中的几个方法遇到了一些问题:我有一个方法，当用户单击 GUI 上的开始按钮时会调用该方法。此方法将接收当前通过网络发送/接收的所有网络流量，并向用户显示相关信息。用户可以通过单击停止按钮来停止调用该方法。该方法目前如下所示:

public static void retrieveFilteredPdu(){

    /*Try/Catch block copied from 'receivePdu()' method in EspduReceiver.java on 07/05/2014
     * Now edit it so that it will receive all PDUs, but only display the ones matching the filter values in the top JTextArea */
    try{
        /*Specify the socket to receive the data */
        EspduReceiver.socket = new MulticastSocket(EspduSender.PORT);
        EspduReceiver.address = InetAddress.getByName(EspduSender.DEFAULT_MULTICAST_GROUP);
        EspduReceiver.socket.joinGroup(EspduReceiver.address); 

        //stopCapture = false;

        /*Loop infinitely, receiving datagrams */
        while(true){
            /*First, set the value of the 'stopCapture' boolean to 'false', in case it has previously been set to true during the life of
             * the program */
            /*stopCapture = false; /*For some reason, if I do this here, clicking the 'Get site' button causes the program to start receiving
            PDUs again, and you are not able to stop it without manually shutting down the program. Possibly because I am infinitely
            setting the value of 'stopCapture' to false?*/

            byte buffer[] = new byte[EspduReceiver.MAX_PDU_SIZE];
            EspduReceiver.packet = new DatagramPacket(buffer, buffer.length);

            EspduReceiver.socket.receive(EspduReceiver.packet);

            Pdu pdu = EspduReceiver.pduFactory.createPdu(EspduReceiver.packet.getData()); /*Moved this line to the top of the class to declare as global variable (29/04/2014) */

            if(pdu != null){
                System.out.print("Got PDU of type: " + pdu.getClass().getName());
                if(pdu instanceof EntityStatePdu){
                    EntityID eid = ((EntityStatePdu)pdu).getEntityID(); 
                    Vector3Double position = ((EntityStatePdu)pdu).getEntityLocation(); 
                    System.out.println(" EID:[" + eid.getSite() + ", " + eid.getApplication() + ", " + eid.getEntity() + "] ");
                    System.out.println("Location in DIS coordinates: [" + position.getX() + ", " + position.getY() + ", " + position.getZ() + "] ");
                    /*Add PDU to ArrayList of PDUs */
                    EspduReceiver.espdu.add(pdu);
    /*              System.out.println(" PDU added to arrayList. "); 
                    System.out.println(espdu); /*This is printing out the actual DIS messages (i.e. edu.nps.moves.dis.EntityState...),
                    maybe try adding the 'eid.getSite()', etc to an ArrayList instead. Use Associative arrays/ map/ hashmap */

                    EspduReceiver.entitySite.add(eid.getSite());
                    System.out.println("Entity Site added to ArrayList from Filter.retrieveFilteredPdu() ");
                    EspduReceiver.entityApplication.add(eid.getApplication());
                    System.out.println("Entity Application added to ArrayLIst. ");
                    EspduReceiver.entity.add(eid.getEntity());
                    System.out.println("Entity ID added to ArrayList");

                    /*Check that everything is actually in the ArrayLists 
                    for(int i : entity){ /*Substituted 'entity' with 'entitySite' and 'entityApplication'- values are all printed correctly. 
                    System.out.println(i);
                    } */

                    /*07/05/2014
                     * Write a method that will only append the PDUs that match the filter values to the text area,
                     * call that method here. */



                    /*Now append each PDU to the text area */
                    Gui.displayFilteredOutput.append("\n");
                    Gui.displayFilteredOutput.append("EID: [" + eid.getSite() + ", " + eid.getApplication() + ", " + eid.getEntity() + "]. ");
                    Gui.displayFilteredOutput.append("Location in DIS coordinates: [" + position.getX() + ", " + position.getY() + ", " + position.getZ() + "] ");

                    /*Append every PDU that matches the filter criteria to the displayFilteredOutput JTextArea 
                    Gui.displayFilteredOutput.append("\n");
                    Gui.displayFilteredOutput.append("EID: [" + eid.getSite() + ", " + eid.getApplication() + ", " + eid.getEntity() + "]. ");
                    Gui.displayFilteredOutput.append("Location in DIS coordinates: [" + position.getX() + ", " + position.getY() + ", " + position.getZ() + "] "); */


                } else if(!(pdu instanceof EntityStatePdu)){
                    System.out.println("There are no PDUs currently being received.");
                }
                System.out.println();
            }
            Thread.sleep(1000);
            /*Try adding a boolean to allow me to stop the capture by clicking 'stop' button- Look on stackoverflow */
            boolean queryStopCapture =  EspduReceiver.stopCapture;
            if(queryStopCapture ==  true){
                System.out.println("Break clause in 'queryStopCapture' if statement in EspduReceiver.java has been called. ");
                break; /*Use a call to receivePdu() to populate the second JTextArea, but don't let it call a 'break' clause at all. 
             *          Find some other way of adding a 'break' to the output displayed in the first JTextArea (01/05/2014)
             *          Maybe add this code to receivePdu() call in ActionListener instead of here.
             */
            } 
        } /*end while */
    } /*end try */
    catch(Exception e){
        System.out.println(e);
        e.printStackTrace();
        System.out.println("Error in retrieveFilteredPdu() method. ");
        /*09/04/2014 @ 17:100
         * If this exception gets called, presumably it either means that pdu is not an instance of EntityStatePdu, or
         * that pdu does not actually hold a packet.  */
    }

}

我有另一种方法，理论上，它应该仅显示有关其属性与用户设置的某些值相匹配的网络流量的信息。当用户单击 GUI 上的“过滤器”按钮时，将调用此方法。该方法目前如下所示:

public static void filterPDUs(){
//  if(EspduReceiver.startCapture == true){
        /*If EspduReceiver.startCapture is true, then the program is already receiving PDUs, so now I need to set it to only display the ones that
         * match the filter criteria. Do this by checking the PDU attributes against the filter values before printing- if they match, then print,
         * if not, don't. */
        if((EspduReceiver.startCapture == true) && (EspduReceiver.stopCapture == false)){
            /*Get the size of the sitesToBeFiltered ArrayList, and store in a variable. Will need to update the variable with every iteration
             * of the loop, because the ArrayList will keep growing as long as the capture is running. */
            int sitesToBeFilteredSize = sitesToBeFiltered.size();
            int matchingSitesIterator = 0;
            /*First, check if site filter value matches the PDU's site, if it does, then check Application, if it matches again, then check ID.
             * If at any point it doesn't match, exit the while loop. */
            while(matchingSitesIterator < sitesToBeFilteredSize){
                System.out.println("SitesToBeFiltered.size() = " + sitesToBeFilteredSize);
                if(sitesToBeFiltered.get(matchingSitesIterator) == Filter.filter1Value){
                    if(applicationsToBeFiltered.get(matchingSitesIterator) == Filter.filter2Value){
                        if(IDsToBeFiltered.get(matchingSitesIterator) == Filter.filter3Value){
                            Gui.displayFilteredOutput.append("Matching PDU found: [" + sitesToBeFiltered.get(matchingSitesIterator) + ", " + applicationsToBeFiltered.get(matchingSitesIterator) + ", " + IDsToBeFiltered.get(matchingSitesIterator) + "] ");
                        } else {Gui.displayFilteredOutput.append("Sorry, there were no PDUs found with the specified ID value.");}
                        Gui.displayFilteredOutput.append("Need to display every PDU that had a matching Site & Application here. ");
                    }else {Gui.displayFilteredOutput.append("Sorry, there were no PDUs found with the specified Application value.");}
                    Gui.displayFilteredOutput.append("need to display every PDU that had a matching Site here. ");
                }else {Gui.displayOutput.append("Sorry, there were no PDUs found with the specified Site value.");}
            }
        } else {
            Gui.displayFilteredOutput.append("Do something if EspduReceiver.startCapture is not true, and EspduReceiver.stopCapture is not false");
        }

//  }else if(EspduReceiver.startCapture == false){
        /*If EspduReceiver.startCapture is false, then the program is not receiving PDUs, so I now need to call the method that will receive PDUs, 
         * and display only the ones that match the filter criteria. */
//  }
}

我遇到的问题是，出于某种原因，如果用户单击“过滤器”按钮仅显示具有匹配过滤条件的 PDU，则在单击“开始”(调用第一个方法)后，程序完全崩溃......(即它似乎停止执行它正在执行的功能，并且不会响应任何按钮甚至“关闭窗口”按钮的点击)

如果他们在单击“开始”和“停止”后单击“过滤”(即当第一个方法未运行时，则第二个方法将按预期执行其任务。

似乎出于某种原因，在第一个方法仍在运行时调用第二个方法会导致程序崩溃 - 我无法弄清楚这是为什么......任何人都可以指出这里出了什么问题吗？

编辑

我的主要方法中有以下代码:

public static void main(String[] args){
    SwingUtilities.invokeLater(new Runnable(){
        @Override
        public void run(){
            Gui gui = new Gui();
            gui.setVisible(true);
        }
    });
}

Answer 1

正如其他人所说，您需要显示更多代码，但如果您使用 Swingworker 或其他线程来运行这些方法，那么这些方法必须是线程安全的或者它们需要同步以防止它们的执行交错​​。如果您在事件分派(dispatch)线程外部直接访问 Swing 组件，那么 Swing 会让您感到烦恼，所以不要这样做(有一些某些文本组件有特殊异常(exception)，但通常是禁止的)。如果您不确定，请在构造或使用 Swing 对象的每个语句之前添加 assert java.awt.EventQueue.isDispatchThread()，并在运行时系统中启用断言。