每当我运行程序时，我都会收到此错误。另外，当按下某些按钮时，不要
根据听众做出回应（我不知道为什么！）
我一起注册了所有按钮
所有按钮使用相同的动作侦听器类
但
仅第3和第4按钮可响应听众，但第1和第2按钮不响应
Exception in thread "main" java.lang.NullPointerException
at IntergrationPoint.<init>(IntergrationPoint.java:73)
at MainLibrary.main(MainLibrary.java:23)
以下是带来所有这些问题的原因。 。 。（我认为也是SSCCE）
import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import static java.awt.image.ImageObserver.WIDTH;
import java.sql.SQLException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTabbedPane;
import javax.swing.UIManager;
/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
/**
*
* @author Yunus
*/
public class IntergrationPoint extends JFrame{
JPanel tabOneContent;
JPanel tabOTwoContent;
JPanel tabThreeContent;
JPanel tabFourContent;
JTabbedPane intergrationTabs;
public JButton createAccount;
public JButton borrowBook;
public JButton returnBook;
public JButton addBook;
public JButton deleteBook;
public JButton deleteMember;
public JButton displayMembers;
public JButton displayAvailableBooks;
public IntergrationPoint()
{
setLookAndFeel();
intergrationTabs = new JTabbedPane();
setSize(761, 430);
setLocationRelativeTo(null);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
tabOneContent = bookOperations();
tabOTwoContent = memberOperations();
intergrationTabs.addTab("<html><body marginheight=30 marginwidth=20>Book Operations<body><html>", null,tabOneContent,"");
intergrationTabs.addTab("<html><body marginheight=30 marginwidth=20>Member Operations<body><html>", null,tabOTwoContent,"");
intergrationTabs.addTab("<html><body marginheight=30 marginwidth=20>Display Members<body><html>", null,memberOperations(),"Display all available member");
intergrationTabs.addTab("<html><body marginheight=30 marginwidth=20>Display Books<body><html>", null,memberOperations(),"Display all available book");
intergrationTabs.addTab("<html><body marginheight=30 marginwidth=20>Login - Logout<body><html>", null,memberOperations(),"Login - Logout");
add(intergrationTabs);
setVisible(true);
setResizable(false);
ButtonListener listener = new ButtonListener();
// Register listener with buttons
borrowBook.addActionListener(listener);
returnBook.addActionListener(listener);
addBook.addActionListener(listener);
deleteBook.addActionListener(listener);
}
class ButtonListener implements ActionListener {
@Override /** Implement actionPerformed */
public void actionPerformed(ActionEvent ev){
if(ev.getSource() == borrowBook)
new BorrowBook();
else if(ev.getSource() == returnBook)
new ReturnBook();
else if(ev.getSource() == addBook)
try {
new AddBook();
} catch (SQLException ex) {
Logger.getLogger(IntergrationPoint.class.getName()).log(Level.SEVERE, null, ex);
}
else if(ev.getSource() == deleteBook)
new DeleteBook();
}
}
public JPanel bookOperations()
{
JPanel panel = new JPanel(new FlowLayout(FlowLayout.LEFT));
JPanel insidePanel = new JPanel(new GridBagLayout());
GridBagConstraints constraints = new GridBagConstraints();
constraints.fill = GridBagConstraints.BOTH;
constraints.anchor = GridBagConstraints.NORTHWEST;
constraints.gridwidth = 1;
constraints.gridheight = 2;
constraints.ipadx = 5;
constraints.ipady = 45;
borrowBook = new JButton("Borrow Book");
returnBook = new JButton("Return Book");
addBook = new JButton("Add Book");
deleteBook = new JButton("Delete Book");
constraints.gridx = 0;
constraints.gridy = 0;
insidePanel.add(borrowBook,constraints);
constraints.gridx = 0;
constraints.gridy = 2;
insidePanel.add(returnBook,constraints);
constraints.gridx = 0;
constraints.gridy = 4;
insidePanel.add(addBook,constraints);
constraints.gridx = 0;
constraints.gridy = 6;
insidePanel.add(deleteBook,constraints);
panel.add(insidePanel);
return panel;
}
public JPanel memberOperations()
{
JPanel panel = new JPanel(new FlowLayout(FlowLayout.LEFT));
JPanel insidePanel = new JPanel(new GridBagLayout());
GridBagConstraints constraints = new GridBagConstraints();
constraints.fill = GridBagConstraints.BOTH;
constraints.anchor = GridBagConstraints.NORTHWEST;
constraints.gridwidth = 1;
constraints.gridheight = 2;
constraints.ipadx = 0;
constraints.ipady = 45;
borrowBook = new JButton("Add Member");
returnBook = new JButton("Delete Member");
constraints.gridx = 0;
constraints.gridy = 0;
insidePanel.add(borrowBook,constraints);
constraints.gridx = 0;
constraints.gridy = 2;
insidePanel.add(returnBook,constraints);
panel.add(insidePanel);
return panel;
}
private void setLookAndFeel()
{
try
{
UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");
}catch(Exception ex)
{
ex.getMessage();
}
}
}
import java.sql.SQLException;
import ui.BorrowBookUI;
import ui.ReturnBookUI;
public class MainLibrary {
public static void main(String[] args) throws SQLException
{
IntergrationPoint intergrationPoint = new IntergrationPoint();
}
}
最佳答案
按钮在memberOperations()和bookOperations()中初始化。例如，您使用的是同一成员borrowBook。但是每次调用memberOperations()都会重新分配它。因此，一旦进入ButtonListener设置，实际上就是在Login - Logout选项卡上的按钮上设置了侦听器。因此，如果切换到该选项卡并单击Add Member，则将触发BorrowBook()操作。
至于NPE，很难说，因为发布的代码只是一个片段，它不包括所有代码，而且不幸的是，没有编译。请发布SSCCE。