Question

所以我有一些看起来像这样的代码：

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Dimension;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.BoxLayout;
import javax.swing.JSeparator;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class IPGUI extends JFrame implements ActionListener 
{
    private static JPanel contentPane;

    private JButton btnConvertDocuments;
    private JButton btnExtractImages;
    private JButton btnParseRIDValues;
    private JButton btnParseImageInfo;

    //Create the frame
    public IPGUI() 
    {
        //Sets frame properties
        setTitle("IP Extractor");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 250, 300);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        contentPane.setLayout(new BorderLayout(0, 0));
        setContentPane(contentPane);

        //Creates new JPanel with boxlayout
        JPanel panel = new JPanel();
        contentPane.add(panel, BorderLayout.CENTER);
        panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));

        //////////////////New Button//////////////////

        JButton btnConvertDocuments = new JButton("1. Convert Documents");
        btnConvertDocuments.setAlignmentX(Component.CENTER_ALIGNMENT);
        btnConvertDocuments.setMaximumSize(new Dimension(160, 0));
        btnConvertDocuments.setPreferredSize(new Dimension(0, 50));

        panel.add(btnConvertDocuments);

        btnConvertDocuments.setActionCommand("w");
        btnConvertDocuments.addActionListener((ActionListener) this);

        JSeparator separator_3 = new JSeparator();
        panel.add(separator_3);

        //////////////////New Button//////////////////

        btnExtractImages = new JButton("2. Extract Images");
        btnExtractImages.setAlignmentX(Component.CENTER_ALIGNMENT);
        btnExtractImages.setMaximumSize(new Dimension(160, 0));
        btnExtractImages.setPreferredSize(new Dimension(0, 50));

        panel.add(btnExtractImages);

        btnExtractImages.setActionCommand("x");
        btnExtractImages.addActionListener((ActionListener) this);

        JSeparator separator_2 = new JSeparator();
        panel.add(separator_2);

        //////////////////New Button//////////////////

        JButton btnParseRIDValues = new JButton("3. Parse rId Values");
        btnParseRIDValues.setAlignmentX(Component.CENTER_ALIGNMENT);
        btnParseRIDValues.setMaximumSize(new Dimension(160, 0));
        btnParseRIDValues.setPreferredSize(new Dimension(0, 50));

        panel.add(btnParseRIDValues);

        btnParseRIDValues.setActionCommand("y");
        btnParseRIDValues.addActionListener((ActionListener) this);

        JSeparator separator_1 = new JSeparator();
        panel.add(separator_1);

        //////////////////New Button//////////////////

        JButton btnParseImageInfo = new JButton("4. Parse Image Info.");
        btnParseImageInfo.setAlignmentX(Component.CENTER_ALIGNMENT);
        btnParseImageInfo.setMaximumSize(new Dimension(160, 0));
        btnParseImageInfo.setPreferredSize(new Dimension(0, 50));

        panel.add(btnParseImageInfo);

        btnParseImageInfo.setActionCommand("z");
        btnParseImageInfo.addActionListener((ActionListener) this);
    }

    //Actions performed when an event occurs.
    public void actionPerformed(ActionEvent event) 
    {
        String command = event.getActionCommand();

        //If btnConvertDocuments is clicked, the FileConverter method is called and the button is then disabled [so as to prevent duplicates].
        if (command.equals("w"))
        {
            FileConverter fc = new FileConverter();
            btnConvertDocuments.setEnabled(false);
        }
        //If btnExtractImages is clicked, the ImageExtractor method is called and the button is then disabled [so as to prevent duplicates].
        else if (command.equals("x"))
        {
            ImageExtractor ie = new ImageExtractor();
            btnExtractImages.setEnabled(false);
        }
        //If btnParseRIDValues is clicked, the XMLIDParser method is called and the button is then disabled [so as to prevent duplicates].
        else if (command.equals("y")) 
        {
            XMLIDParser xip = new XMLIDParser();
            btnParseRIDValues.setEnabled(false);
        }
        //If btnParseImageInfo is clicked, the XMLTagParser method is called and the button is then disabled [so as to prevent duplicates].
        else if (command.equals("z")) 
        {
            XMLTagParser xtp = new XMLTagParser();
            btnParseImageInfo.setEnabled(false);        
        }
    }
}

主要

import java.awt.EventQueue;

public class IPDriver 
{
    public static void main(String[] args) 
    {   
        //Calls GUI and sets its visibility to true
        EventQueue.invokeLater(new Runnable() 
        {
            public void run() 
            {
                try 
                {
                    IPGUI frame = new IPGUI();
                    frame.setVisible(true);
                } 
                catch (Exception e)
                {
                    e.printStackTrace();
                }
            }
        });
    }
}

错误产生

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at IPGUI.actionPerformed(IPGUI.java:119)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

所以我认为错误来自我的主要调用EventQueue的地方。当我拿出来......

 EventQueue.invokeLater(new Runnable() 
        {
            public void run() 
            {

...除了try catch语句之外什么都没有，一切似乎工作正常，按钮被禁用。但是，我只是想知道是否有必要将EventQueue语句留在那里，它的重要性是什么？

也是一个相关的问题。我试图运行这个扩展数量的文件夹（~100）和按钮1-3工作正常，但在按钮4，它到达第18个文件夹，GUI只是冻结。我想知道是否有办法阻止冻结？

提前感谢您的帮助！

Answer 1

你的IPGUI构造函数中有一个本地btnConvertDocuments，它掩盖了类btnConvertDocuments对象。

只是

    btnConvertDocuments = new JButton("1. Convert Documents");
    btnConvertDocuments.setAlignmentX(Component.CENTER_ALIGNMENT);
    btnConvertDocuments.setMaximumSize(new Dimension(160, 0));
    btnConvertDocuments.setPreferredSize(new Dimension(0, 50));

等。其他按钮

Answer 2

错误确实来自main，因为这是应用程序启动的地方。但是，错误发生是因为btnParseRIDValues null

在下面的代码段中，通过重新定义变量来覆盖某个类变量;

JButton btnParseRIDValues = new JButton("3. Parse rId Values");

尝试将其更改为：

btnParseRIDValues = new JButton("3. Parse rId Values");

如果按btnParseImageInfo或btnConvertDocuments，则会发生同样的错误。

JButton btnParseImageInfo = new JButton("4. Parse Image Info.");
JButton btnConvertDocuments = new JButton("1. Convert Documents");

需要更改为：

btnParseImageInfo = new JButton("4. Parse Image Info.");
btnConvertDocuments = new JButton("1. Convert Documents");

修改*

为防止GUI冻结，您可以运行线程化的操作：

new Thread(new Runnable() { public void run() { FileConverter fc = new FileConverter(); } }).start();

有关详细信息，请参阅http://www.javabeginner.com/learn-java/java-threads-tutorial。

JAVA GUI按钮问题

2 个答案: