在Java JFrame中显示通过网络接收的信息

我正在用Java编写一个程序，允许用户查看通过网络发送/接收的DIS（分布式交互模拟）。我目前已经设置了程序，以便它读取信息，并在控制台中显示它-只要它在运行（即，直到我单击“停止”）它就会这样做

我现在正试图创建一个GUI来向用户显示这些信息。我有一个

Gui.java

类，还有一个

EspduReceiver.java

类，在这里我读取通过网络发送的DIS信息，并将其显示在控制台中

现在，我想通过Gui类向用户显示正在读取到程序中的DIS信息

我的Gui类当前如下所示：

package openDIS;

import java.applet.*;
import java.awt.*;
import javax.swing.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class Gui extends JFrame{

public Gui(){
    setTitle("DIS Filter");
    setSize(1000, 500);
    setLocation (10, 10);
    setDefaultCloseOperation(EXIT_ON_CLOSE);

    initGui();
}

/*public quitButton(){
    initGui();
} */

private void initGui(){
    JFrame frame = new JFrame();
    JPanel panel = new JPanel();

    frame.getContentPane().add(panel);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setTitle("DIS Filter");
    frame.setSize(1000, 500);

    panel.setLayout(null);

    /*Create a String to hold the PDU information to be displayed in the JTextArea */
    String output = EspduReceiver.pdu;

    /*Add a JTextArea to display the output DIS information */
    //JTextArea output = new JTextArea();
    panel.add(new JTextArea(output));

    JButton quitButton = new JButton("Quit");
    quitButton.setBounds(875, 400, 80, 30); /*Set the location of the button in the window, and its size */

    quitButton.addActionListener(new ActionListener(){
        @Override
        public void actionPerformed(ActionEvent e){
            System.exit(0);
        }
    });


    panel.add(quitButton);
    setTitle("Quit");
    //setSize(60,30); /*This line was overwriting the previously set values for the size of the window */
    setLocationRelativeTo(null);
    setDefaultCloseOperation(EXIT_ON_CLOSE);        
}

public static void main(String[] args){ /* I probably don't need a main method here- I have one in EspduReceiver.java */
    SwingUtilities.invokeLater(new Runnable(){
        @Override
        public void run(){
            Gui gui = new Gui();
            gui.setVisible(true);
        }
    });
}




}

package openDIS;

import java.net.*;
import java.applet.*;
import java.awt.*;

import edu.nps.moves.disutil.*;
import edu.nps.moves.dis.*;

/*Receives PDUs from the network in IEEE format. */

public class EspduReceiver {

/*Max size of a PDU in binary format that we can receive. Outdated- PDUs can be larger- but this is a reasonable starting point */
public static final int MAX_PDU_SIZE = 8192;

public static void main(String args[]){

    MulticastSocket socket;
    DatagramPacket packet;
    InetAddress address;
    PduFactory pduFactory = new PduFactory();

    try{
        /*Specify the socket to receive the data */
        socket = new MulticastSocket(EspduSender.PORT);
        address = InetAddress.getByName(EspduSender.DEFAULT_MULTICAST_GROUP);
        socket.joinGroup(address); 

        /*Loop infinitely, receiving datagrams */
        while(true){
            byte buffer[] = new byte[MAX_PDU_SIZE];
            packet = new DatagramPacket(buffer, buffer.length);

            socket.receive(packet);

            Pdu pdu = pduFactory.createPdu(packet.getData());

            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.print(" EID:[" + eid.getSite() + ", " + eid.getApplication() + ", " + eid.getEntity() + "] ");
                    System.out.print(" 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();
            }
        } /*end while */
    } /*end try */
    catch(Exception e){
        System.out.println(e);
        e.printStackTrace();
        System.out.println("This is where the error is being generated");
        /*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.  */
    }
} /*end main */

} /*end class */

我的EspduReceiver课程目前看起来是这样的：

package openDIS;

import java.applet.*;
import java.awt.*;
import javax.swing.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class Gui extends JFrame{

public Gui(){
    setTitle("DIS Filter");
    setSize(1000, 500);
    setLocation (10, 10);
    setDefaultCloseOperation(EXIT_ON_CLOSE);

    initGui();
}

/*public quitButton(){
    initGui();
} */

private void initGui(){
    JFrame frame = new JFrame();
    JPanel panel = new JPanel();

    frame.getContentPane().add(panel);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setTitle("DIS Filter");
    frame.setSize(1000, 500);

    panel.setLayout(null);

    /*Create a String to hold the PDU information to be displayed in the JTextArea */
    String output = EspduReceiver.pdu;

    /*Add a JTextArea to display the output DIS information */
    //JTextArea output = new JTextArea();
    panel.add(new JTextArea(output));

    JButton quitButton = new JButton("Quit");
    quitButton.setBounds(875, 400, 80, 30); /*Set the location of the button in the window, and its size */

    quitButton.addActionListener(new ActionListener(){
        @Override
        public void actionPerformed(ActionEvent e){
            System.exit(0);
        }
    });


    panel.add(quitButton);
    setTitle("Quit");
    //setSize(60,30); /*This line was overwriting the previously set values for the size of the window */
    setLocationRelativeTo(null);
    setDefaultCloseOperation(EXIT_ON_CLOSE);        
}

public static void main(String[] args){ /* I probably don't need a main method here- I have one in EspduReceiver.java */
    SwingUtilities.invokeLater(new Runnable(){
        @Override
        public void run(){
            Gui gui = new Gui();
            gui.setVisible(true);
        }
    });
}




}

package openDIS;

import java.net.*;
import java.applet.*;
import java.awt.*;

import edu.nps.moves.disutil.*;
import edu.nps.moves.dis.*;

/*Receives PDUs from the network in IEEE format. */

public class EspduReceiver {

/*Max size of a PDU in binary format that we can receive. Outdated- PDUs can be larger- but this is a reasonable starting point */
public static final int MAX_PDU_SIZE = 8192;

public static void main(String args[]){

    MulticastSocket socket;
    DatagramPacket packet;
    InetAddress address;
    PduFactory pduFactory = new PduFactory();

    try{
        /*Specify the socket to receive the data */
        socket = new MulticastSocket(EspduSender.PORT);
        address = InetAddress.getByName(EspduSender.DEFAULT_MULTICAST_GROUP);
        socket.joinGroup(address); 

        /*Loop infinitely, receiving datagrams */
        while(true){
            byte buffer[] = new byte[MAX_PDU_SIZE];
            packet = new DatagramPacket(buffer, buffer.length);

            socket.receive(packet);

            Pdu pdu = pduFactory.createPdu(packet.getData());

            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.print(" EID:[" + eid.getSite() + ", " + eid.getApplication() + ", " + eid.getEntity() + "] ");
                    System.out.print(" 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();
            }
        } /*end while */
    } /*end try */
    catch(Exception e){
        System.out.println(e);
        e.printStackTrace();
        System.out.println("This is where the error is being generated");
        /*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.  */
    }
} /*end main */

} /*end class */

目前，当我尝试运行Gui.java类时，我得到一个错误，行

String output=EspduReceiver.pdu-上面写着：

线程“AWT-EventQueue-0”java.lang中出现异常。错误：未解决的编译问题：pdu无法解决或不是字段

我想知道这是否是因为我的
pdu
变量是在我的espdureciver.java类中的
try-catch
方法中创建的，因此对该代码块之外的任何东西都不可见？我尝试在espdureciver.java类中将其声明为全局变量，但这导致了几个新的错误

有人能告诉我如何将Gui.java类中的
输出
字符串的值设置为espdureciver.java类中的
pdu
变量的值吗？或者我应该使用另一种数据类型而不是字符串来保存它吗？基本上，我如何通过使用我的Gui.java类

谢谢

编辑2014年4月15日

嘿，谢谢你的回答-我已经尝试了你的建议，但是我在
pdu=pduFactory.createPdu（packet.getData（））；
这行上遇到了一个错误，它说：“无法对非静态字段pdu进行静态引用。”。“我更改了
公共Pdu Pdu至<代码>公共静态Pdu Pdu，这样就消除了这个错误，但是现在当我尝试运行我的EspduReceiver.java类时，什么也没有发生

我的Gui.java类现在可以编译了，但是当我尝试运行它时，控制台会显示一条消息：“线程中的异常”AWT-EventQueue-0“java.lang.NullPointerException”。它在抱怨以下几句话：

initGui();

String output = EspduReceiver.pdu.toString();

Gui gui = new Gui();

如果您正在键入
espddureceiver.pdu
，这意味着您希望获得
espddureceiver
类的
pdu
字段的值。但是这个类没有这样的字段。因此，只需添加以下内容：

public class EspduReceiver {
    public static final int MAX_PDU_SIZE = 8192;
    public static Pdu pdu;
    ...
}

并将其替换为：

 Pdu pdu = pduFactory.createPdu(packet.getData());

为此：

 pdu = pduFactory.createPdu(packet.getData());

但是稍后，在GUI类中，您应该获得
pdu
的
String
内容。我从来没有遇到过这个类，但是如果它是一个描述的类，我认为您可以通过以下方式获得数据：

String output = EspduReceiver.pdu.toString();

嘿，谢谢你的回答-我已经试着做了你建议的更改，但我仍然遇到一些问题-我修改了我原来的问题，以显示所做的更改和我现在遇到的错误。@someone2088我的打字错误，编辑了我的答案，你应该把它设置为
static
nikis-我试过了-正如我在编辑我原来的帖子中提到的那样。这消除了错误，但现在当我尝试运行espdureciver.java类时什么也没有发生，我的Gui.java类中又出现了一个错误…@someone2088您应该在
createPdu
执行之后检查
pdu
的值我想您的意思是通过在控制台中打印来检查值？我不能这样做，因为我的类不再运行——正如我在编辑中提到的那样。我在尝试运行EspduReceiver.java类时根本没有得到任何输出。。。当尝试运行Gui.java类时，我得到了我提到的NullPointerException。。。有没有关于如何解决这些问题的建议？