我必须为我的java类简介制作一个项目，在最终整理出语法错误之后，当我点击播放或保存按钮时，我在这个程序中遇到运行时错误。
//C:\\Users\\Andrew\\Downloads\\never gonna give you up.wav
//Andrew Douglas
//Imports
import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import javax.sound.sampled.*;
import javax.swing.filechooser.*;
import javax.swing.JTable;
//Creates class
public class JPlayer extends JFrame implements ActionListener {
//Sets up form items and necessary globals
JButton save, play, stop, loop;
JFileChooser dialog;
JTable table;
String Artist, Song, Album, Loc;
Object[][] data;
int n = 1;
//Makes the library, with a 51 song limit.
JLibrary[] addedSong = new JLibrary[50];
public JPlayer() {
super ("JPlayer");
//Creates frame
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setTitle("jPlayer");
this.setSize(800, 600);
//Makes titles for table
String[] columnNames = {"Artist",
"Song",
"Album",
"Location"};
//Gives one value for array
addedSong[0] = new JLibrary ("Rick Astley", "NGGYU", "UnKnown", "C:\\Users\\Andrew\\Downloads\\never gonna give you up.wav");
//Adds it to table array
Object[][] data = {
{
(addedSong[0].returnArtist()), (addedSong[0].returnSong()), (addedSong[0].returnAlbum()), (addedSong[0].returnFile())
}
};
//Creates table
JTable table = new JTable(data, columnNames);
table.setPreferredScrollableViewportSize(new Dimension(500, 70));
table.setFillsViewportHeight(true);
//Lets it sort the rows
table.setAutoCreateRowSorter(true);
//Creates the scroller
JScrollPane scrollPane = new JScrollPane(table);
//Makes the save file dialog and the play and save buttons
dialog = new JFileChooser();
play = new JButton ("Play Song");
save = new JButton ("Save a file");
//Adds the button listeners
save.addActionListener(this);
play.addActionListener(this);
//Adds buttons to panel
JPanel buttons = new JPanel();
buttons.add(save);
buttons.add(play);
//Puts the buttons at the bottom
add(buttons, BorderLayout.SOUTH);
add(scrollPane);
this.setVisible(true);
}
//Creates action listener for button
public void actionPerformed(ActionEvent e) {
if (e.getSource() == save) {
dialog.setFileFilter(new FileNameExtensionFilter("Wave File (*.wav)"));
int returnVal = dialog.showSaveDialog(JPlayer.this);
if (returnVal == dialog.APPROVE_OPTION) {
File file = dialog.getSelectedFile();
addToLibrary("", "", "", file.getName());
}
}
else if (e.getSource() == play) {
String holder2;
Object holder;
holder = table.getValueAt(table.getSelectedRow(), 3);
try {
File soundFile = new File(holder.toString());
AudioInputStream audioIn = AudioSystem.getAudioInputStream(soundFile);
Clip clip = AudioSystem.getClip();
clip.open(audioIn);
clip.start();
} catch (UnsupportedAudioFileException f) {
f.printStackTrace();
} catch (IOException f) {
f.printStackTrace();
} catch (LineUnavailableException f) {
f.printStackTrace();
}
} }
public static void main(String[]args) {
new JPlayer();
}
public void addToLibrary(String art, String song, String alb, String file) {
addedSong[n] = new JLibrary(art, song, alb, file);
int j = 0;
while (n >= 0) {
Object[][] data = {
{
addedSong[(n-j)],
}
};
j = j+1;
}
n = n +1;
}
}
每当我点击播放按钮开始播放文件中的音乐时，我都会收到此错误：
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at JPlayer.actionPerformed(JPlayer.java:86)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:729)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:688)
at java.awt.EventQueue$3.run(EventQueue.java:686)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:702)
at java.awt.EventQueue$4.run(EventQueue.java:700)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:699)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
当我点击保存按钮时，我收到此错误：
Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException: Extensions must be non-null and not empty
at javax.swing.filechooser.FileNameExtensionFilter.<init>(FileNameExtensionFilter.java:76)
at JPlayer.actionPerformed(JPlayer.java:75)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:729)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:688)
at java.awt.EventQueue$3.run(EventQueue.java:686)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:702)
at java.awt.EventQueue$4.run(EventQueue.java:700)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:699)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
有人可以通过告诉我什么是错的或如何解决它来帮助我吗？任何帮助将不胜感激，我对这些东西有点慢：）
答案 0 :(得分：0)
对于播放按钮错误：通过计算行数（75 - > 86），我推断错误在此声明中
holder = table.getValueAt(table.getSelectedRow(), 3);
这是因为table（字段）为null。在构造函数中，您将填充一个名为table的局部变量，该变量隐藏了同名字段。 替换
JTable table = new JTable(data, columnNames);
通过
table = new JTable(data, columnNames);
对于保存按钮错误，似乎应该将“wav”作为FileNameExtensionFilter的构造函数的第二个参数提供