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我想创建一个空的 .ser 文件来存储对象的数组列表(如果尚未创建),以便稍后在程序中使用。在弄清楚我当前的问题后,我将在稍后添加是否存在检查。我的 File = new File(etc 等) 行上出现空指针异常。这是屏幕截图的更好解释。
编辑:添加源代码
/*
* To change this license header, choose License Headers in Project
Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
package dark.rusty;
import java.awt.Color;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.ArrayList;
/**
*
* @author UoD
*/
public class Gui extends javax.swing.JFrame {
/**
* Creates new form Gui
*/
public Gui() {
initComponents();
setLocationRelativeTo(null);
setTitle("CMS - Dark&Rusty");
this.getContentPane().setBackground(new Color(190, 190, 190));
MenuItem a = new MenuItem("temp", 0, 0);
ArrayList<MenuItem> tempAList = new ArrayList<MenuItem>();
createFileIFN();
}
private void createFileIFN() {
try {
File myFile = new File((this.getClass().getResource("/text/menu.ser").toString());
if (myFile.createNewFile()) {
System.out.println("File is created!");
} else {
System.out.println("File already exists.");
}
} catch (IOException e) {
e.printStackTrace();
}
}
private ArrayList<MenuItem> getArrList(File tempFile) {
ArrayList<MenuItem> items = new ArrayList<MenuItem>();
MenuItem tempItem;
try {
FileInputStream fileIn = new FileInputStream(tempFile);
ObjectInputStream in = new ObjectInputStream(fileIn);
tempItem = (MenuItem) in.readObject();
in.close();
fileIn.close();
} catch (IOException i) {
i.printStackTrace();
} catch (ClassNotFoundException c) {
System.out.println("Employee class not found");
c.printStackTrace();
}
return items;
}
private void writeItemtoFile(MenuItem a, File tempFile) {
try {
FileOutputStream fos = new FileOutputStream(tempFile);
ObjectOutputStream oos = new ObjectOutputStream(fos);
// write object to file
oos.writeObject(a);
// closing resources
oos.close();
fos.close();
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* This method is called from within the constructor to initialize the form.
* WARNING: Do NOT modify this code. The content of this method is always
* regenerated by the Form Editor.
*/
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">
private void initComponents() {
jPanel1 = new javax.swing.JPanel();
jButton7 = new javax.swing.JButton();
jButton8 = new javax.swing.JButton();
jPanel2 = new javax.swing.JPanel();
jScrollPane2 = new javax.swing.JScrollPane();
jList2 = new javax.swing.JList<>();
jButton6 = new javax.swing.JButton();
jPanel3 = new javax.swing.JPanel();
jLabel1 = new javax.swing.JLabel();
jLabel2 = new javax.swing.JLabel();
jLabel3 = new javax.swing.JLabel();
jLabel4 = new javax.swing.JLabel();
jLabel5 = new javax.swing.JLabel();
jLabel6 = new javax.swing.JLabel();
jButton9 = new javax.swing.JButton();
jButton10 = new javax.swing.JButton();
jScrollPane3 = new javax.swing.JScrollPane();
jList3 = new javax.swing.JList<>();
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
setBackground(new java.awt.Color(190, 190, 190));
setResizable(false);
setSize(new java.awt.Dimension(800, 600));
jPanel1.setBackground(new java.awt.Color(190, 190, 190));
jPanel1.setPreferredSize(new java.awt.Dimension(800, 50));
jButton7.setIcon(new javax.swing.ImageIcon(getClass().getResource("/images/if_Sidebar_Left_Interface_Menu_Window_1654369.png"))); // NOI18N
jButton7.setHorizontalTextPosition(javax.swing.SwingConstants.CENTER);
jButton7.setMargin(new java.awt.Insets(2, 20, 2, 20));
jButton7.setPreferredSize(new java.awt.Dimension(32, 32));
jPanel1.add(jButton7);
jButton8.setIcon(new javax.swing.ImageIcon(getClass().getResource("/images/if_TaskStroke_1737368.png"))); // NOI18N
jButton8.setHorizontalTextPosition(javax.swing.SwingConstants.CENTER);
jButton8.setMargin(new java.awt.Insets(2, 20, 2, 20));
jButton8.setPreferredSize(new java.awt.Dimension(32, 32));
jPanel1.add(jButton8);
jPanel2.setBackground(new java.awt.Color(190, 190, 190));
javax.swing.GroupLayout jPanel2Layout = new javax.swing.GroupLayout(jPanel2);
jPanel2.setLayout(jPanel2Layout);
jPanel2Layout.setHorizontalGroup(
jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGap(0, 800, Short.MAX_VALUE)
);
jPanel2Layout.setVerticalGroup(
jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGap(0, 100, Short.MAX_VALUE)
);
jScrollPane2.setPreferredSize(new java.awt.Dimension(300, 120));
jList2.setBackground(new java.awt.Color(190, 190, 190));
jList2.setBorder(javax.swing.BorderFactory.createMatteBorder(2, 2, 2, 2, new java.awt.Color(240, 240, 240)));
jList2.setFont(new java.awt.Font("Rockwell", 1, 14)); // NOI18N
jList2.setModel(new javax.swing.AbstractListModel<String>() {
String[] strings = { "Item 1", "Item 2", "Item 3", "Item 4", "Item 5" };
public int getSize() { return strings.length; }
public String getElementAt(int i) { return strings[i]; }
});
jList2.setSelectionMode(javax.swing.ListSelectionModel.SINGLE_SELECTION);
jList2.setPreferredSize(new java.awt.Dimension(290, 80));
jScrollPane2.setViewportView(jList2);
jButton6.setIcon(new javax.swing.ImageIcon(getClass().getResource("/images/if_Tick_1737369 (1).png"))); // NOI18N
jButton6.setHorizontalTextPosition(javax.swing.SwingConstants.CENTER);
jButton6.setPreferredSize(new java.awt.Dimension(32, 32));
jButton6.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
jButton6ActionPerformed(evt);
}
});
jPanel3.setBackground(new java.awt.Color(190, 190, 190));
jPanel3.setPreferredSize(new java.awt.Dimension(290, 136));
jLabel1.setFont(new java.awt.Font("Poiret One", 1, 24)); // NOI18N
jLabel1.setForeground(new java.awt.Color(51, 102, 0));
jLabel1.setText("Kalan:");
jLabel1.setPreferredSize(new java.awt.Dimension(120, 30));
jLabel2.setFont(new java.awt.Font("Poiret One", 1, 24)); // NOI18N
jLabel2.setForeground(new java.awt.Color(204, 0, 51));
jLabel2.setText("Odenen:");
jLabel2.setPreferredSize(new java.awt.Dimension(120, 30));
jLabel3.setFont(new java.awt.Font("Poiret One", 1, 24)); // NOI18N
jLabel3.setForeground(new java.awt.Color(0, 153, 255));
jLabel3.setText("0");
jLabel3.setToolTipText("");
jLabel3.setPreferredSize(new java.awt.Dimension(120, 30));
jLabel4.setFont(new java.awt.Font("Poiret One", 1, 24)); // NOI18N
jLabel4.setForeground(new java.awt.Color(51, 102, 0));
jLabel4.setText("5.00");
jLabel4.setPreferredSize(new java.awt.Dimension(120, 30));
jLabel5.setFont(new java.awt.Font("Poiret One", 1, 24)); // NOI18N
jLabel5.setForeground(new java.awt.Color(204, 0, 51));
jLabel5.setText("13.00");
jLabel5.setPreferredSize(new java.awt.Dimension(120, 30));
jLabel6.setFont(new java.awt.Font("Poiret One", 1, 24)); // NOI18N
jLabel6.setForeground(new java.awt.Color(0, 153, 255));
jLabel6.setText("İptal:");
jLabel6.setPreferredSize(new java.awt.Dimension(120, 30));
javax.swing.GroupLayout jPanel3Layout = new javax.swing.GroupLayout(jPanel3);
jPanel3.setLayout(jPanel3Layout);
jPanel3Layout.setHorizontalGroup(
jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(jPanel3Layout.createSequentialGroup()
.addContainerGap()
.addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(jPanel3Layout.createSequentialGroup()
.addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 40, Short.MAX_VALUE)
.addComponent(jLabel4, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGroup(jPanel3Layout.createSequentialGroup()
.addComponent(jLabel2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(jLabel5, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, jPanel3Layout.createSequentialGroup()
.addComponent(jLabel6, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(jLabel3, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)))
.addContainerGap())
);
jPanel3Layout.setVerticalGroup(
jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(jPanel3Layout.createSequentialGroup()
.addContainerGap()
.addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(jLabel4, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
.addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(jLabel2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(jLabel5, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 13, Short.MAX_VALUE)
.addGroup(jPanel3Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(jLabel3, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(jLabel6, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
.addContainerGap())
);
jButton9.setIcon(new javax.swing.ImageIcon(getClass().getResource("/images/if_Dollar_1737376(1).png"))); // NOI18N
jButton9.setHorizontalTextPosition(javax.swing.SwingConstants.CENTER);
jButton9.setPreferredSize(new java.awt.Dimension(32, 32));
jButton10.setIcon(new javax.swing.ImageIcon(getClass().getResource("/images/if_Wrong_1737371.png"))); // NOI18N
jButton10.setHorizontalTextPosition(javax.swing.SwingConstants.CENTER);
jButton10.setPreferredSize(new java.awt.Dimension(32, 32));
jScrollPane3.setPreferredSize(new java.awt.Dimension(300, 120));
jList3.setBackground(new java.awt.Color(190, 190, 190));
jList3.setBorder(javax.swing.BorderFactory.createMatteBorder(2, 2, 2, 2, new java.awt.Color(240, 240, 240)));
jList3.setFont(new java.awt.Font("Rockwell", 1, 14)); // NOI18N
jList3.setSelectionMode(javax.swing.ListSelectionModel.SINGLE_SELECTION);
jList3.setPreferredSize(new java.awt.Dimension(290, 80));
jScrollPane3.setViewportView(jList3);
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addGroup(layout.createSequentialGroup()
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING, false)
.addComponent(jPanel2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addGroup(layout.createSequentialGroup()
.addGap(6, 6, 6)
.addComponent(jScrollPane2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addComponent(jButton6, javax.swing.GroupLayout.PREFERRED_SIZE, 32, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(jButton9, javax.swing.GroupLayout.PREFERRED_SIZE, 32, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGroup(layout.createSequentialGroup()
.addGap(0, 0, Short.MAX_VALUE)
.addComponent(jButton10, javax.swing.GroupLayout.PREFERRED_SIZE, 32, javax.swing.GroupLayout.PREFERRED_SIZE)))
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
.addComponent(jScrollPane3, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addGap(10, 10, 10)))
.addGap(0, 0, Short.MAX_VALUE))
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
.addContainerGap(javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(jPanel3, javax.swing.GroupLayout.PREFERRED_SIZE, 300, javax.swing.GroupLayout.PREFERRED_SIZE)
.addContainerGap())
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
.addComponent(jPanel2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
.addComponent(jButton6, javax.swing.GroupLayout.PREFERRED_SIZE, 32, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(jScrollPane2, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addGroup(layout.createSequentialGroup()
.addComponent(jButton9, javax.swing.GroupLayout.PREFERRED_SIZE, 32, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(jButton10, javax.swing.GroupLayout.PREFERRED_SIZE, 32, javax.swing.GroupLayout.PREFERRED_SIZE)))
.addComponent(jScrollPane3, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(jPanel3, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 182, Short.MAX_VALUE)
.addComponent(jPanel1, javax.swing.GroupLayout.PREFERRED_SIZE, 50, javax.swing.GroupLayout.PREFERRED_SIZE))
);
pack();
}// </editor-fold>
private void jButton6ActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
}
/**
* @param args the command line arguments
*/
public static void main(String args[]) {
/* Set the Nimbus look and feel */
//<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
/* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
* For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html
*/
try {
for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
if ("Nimbus".equals(info.getName())) {
javax.swing.UIManager.setLookAndFeel(info.getClassName());
break;
}
}
} catch (ClassNotFoundException ex) {
java.util.logging.Logger.getLogger(Gui.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (InstantiationException ex) {
java.util.logging.Logger.getLogger(Gui.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (IllegalAccessException ex) {
java.util.logging.Logger.getLogger(Gui.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (javax.swing.UnsupportedLookAndFeelException ex) {
java.util.logging.Logger.getLogger(Gui.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
}
//</editor-fold>
/* Create and display the form */
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new Gui().setVisible(true);
}
});
}
// Variables declaration - do not modify
private javax.swing.JButton jButton10;
private javax.swing.JButton jButton6;
private javax.swing.JButton jButton7;
private javax.swing.JButton jButton8;
private javax.swing.JButton jButton9;
private javax.swing.JLabel jLabel1;
private javax.swing.JLabel jLabel2;
private javax.swing.JLabel jLabel3;
private javax.swing.JLabel jLabel4;
private javax.swing.JLabel jLabel5;
private javax.swing.JLabel jLabel6;
private javax.swing.JList<String> jList2;
private javax.swing.JList<String> jList3;
private javax.swing.JPanel jPanel1;
private javax.swing.JPanel jPanel2;
private javax.swing.JPanel jPanel3;
private javax.swing.JScrollPane jScrollPane2;
private javax.swing.JScrollPane jScrollPane3;
// End of variables declaration
}
最佳答案
this.getClass().getResource("/text/menu.ser")
如果
"/text/menu.ser"
不存在,
将返回null
。因此,
this.getClass().getResource("/text/menu.ser").toString()
将导致NullPointerException
。
此外,getResource
返回一个 URL
实例,并且 URL
的字符串表示(例如 file:/home/user3524633/text/menu.ser
)与本地文件系统路径(这是您要与 File
构造函数一起使用的路径)不同。
您为什么首先使用getResource
?您是否正在尝试确定相对于应用程序类的路径?
关于Java 在资源文件夹上创建一个空的 .ser 文件(如果尚不存在),我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/51265054/
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在以下代码中,第一个日志语句按预期显示小数,但第二个日志语句记录 NULL。我做错了什么? NSDictionary *entry = [[NSDictionary alloc] initWithOb
我正在使用与此类似的代码动态添加到数组; $arrayF[$f+1][$y][$x+1] = $value+1; 但是我在错误报告中收到了这个: undefined offset :1 问题:尝试创
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