我无法弄清楚我的计划有什么问题。有3个类，Owner是单例，因此当GUI请求Owner实例时，getOwner()中的Owner方法会返回先前保存的Owner ，否则返回新的Owner。我认为序列化是正确实现的。 Map cars集合是暂时的，退出时无需保存。
当程序第一次运行时，用户可以通过按下gui中的任意一个按钮来执行intoMap1()或intoMap2()方法，其中Owner方法在addCar()方法中要求Map创建汽车并使用键A1或/和B2插入其Map集合。我检查过每个程序运行后cars Owner包含1或2辆汽车，所以没有问题。
当程序关闭并再次打开时，Cars.ser已保存并在addCar()文件中反序列化且没有错误，我用print语句检查了它。问题是当程序再次运行Owner时cars创建新车，但没有将其添加到Map cars，这会导致异常。地图A1未保存，因此它是空的，无论如何即使在第一次运行中我插入地图车B2，它也不会在第二次运行中插入新车Map。 Cars.ser是暂时的，有什么不对吗？为什么它不能在第二轮中添加汽车来映射？如果我删除Map文件，则在第一次运行时再次添加汽车。似乎在第二轮中name;不想合作。在第二次运行中，使用先前保存的字段Owner创建新对象。散列是否会导致问题？
仅在cars.containsKey(regNumIn)第34行的第二次运行中导致异常，public class GUI extends javax.swing.JFrame
{
Owner owne;
public GUI()
{
owne = Owner.getOwner(); //name is correctly retrieved each time
System.out.println(owne.toString()); //name is printed each time
addWindowListener(new CloseQuit());
initComponents();
}
public void intoMap1() //executed by pressing button in gui, asking owne object to create and add car
{
owne.addCar("A1", "red", 6); //Line 36
}
public void intoMap2() //executed by pressing button in gui, asking owne object to add cars
{
41 owne.addCar("B2", "black", 4); //Line 41
}
private class CloseQuit extends WindowAdapter
{
public void windowClosing(WindowEvent e)
{
System.out.println("CloseQuit executed");
owne.saveOwner();
}
}
}
在第45行因某种原因失败。
public class Owner implements Serializable
{
String name;
transient Map<String, Car> cars;
public Owner()
{
name = "John";
cars = new HashMap<>();
}
public void addCar(String regNumIn, String colourIn, int doorsIn)
{
Car car = new Car(regNumIn, colourIn, doorsIn); //works in each execution
System.out.println("Car is created" + car.toString());
try
{
34 cars.put(regNumIn, car); //Line 34, works only when program runs first time,
//after Owner is deserialized it doesnt add cars with new keys, exception
}
catch (Exception ex)
{
System.out.println("Exception in Owner when adding car ");
ex.printStackTrace();
}
try
{
45 System.out.println("Map has key " + regNumIn + ": " + cars.containsKey(regNumIn)); //Line 45
}
catch (Exception ex)
{
ex.printStackTrace();
}
System.out.println("--------------------------------------------------------------------");
}
public static Owner getOwner() //works fine
{
Owner owne = null;
try
{
FileInputStream fis = new FileInputStream("Cars.ser");
ObjectInputStream ois = new ObjectInputStream(fis);
owne = (Owner) ois.readObject(); ois.close();
}
catch(FileNotFoundException ex)
{
owne = new Owner(); //creates new Owner if run for first time
}
catch (Exception ex)
{
System.exit(0);
}
return owne;
}
public void saveOwner() //works fine
{
try
{
FileOutputStream fis = new FileOutputStream("Cars.ser");
ObjectOutputStream ois = new ObjectOutputStream(fis);
ois.writeObject(this); ois.close();
}
catch(Exception ex)
{
System.out.println("Can't store state of owner");
System.exit(0);
}
}
@Override
public String toString()
{
return ("name = " + name);
}
}
public class Car
{
String regNum;
String colour;
int doors;
public Car(String regNumIn, String colourIn, int doorsIn)
{
regNum = regNumIn;
colour = colourIn;
doors = doorsIn;
}
public String toString()
{
return ("regNum = " + regNum );
}
}
run:
--------------
name = John
--------------
Car is created: regNum = A1
Map has key A1: true
--------------------------------------------------------------------
Car is created: regNum = B2
Map has key B2: true
--------------------------------------------------------------------
CloseQuit executed
BUILD SUCCESSFUL (total time: 8 seconds)
首次运行后输出为：
run:
--------------
name = John
--------------
Car is created: regNum = A1
Exception in Owner when adding car
java.lang.NullPointerException
at core.Owner.addCar(Owner.java:34)
at gui.GUI.intoMap1(GUI.java:36)
at gui.GUI.jButton1ActionPerformed(GUI.java:215)
at gui.GUI.access$100(GUI.java:17)
at gui.GUI$1.actionPerformed(GUI.java:87)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
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:6535)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
at java.awt.Component.processEvent(Component.java:6300)
at java.awt.Container.processEvent(Container.java:2236)
at java.awt.Component.dispatchEventImpl(Component.java:4891)
at java.awt.Container.dispatchEventImpl(Container.java:2294)
at java.awt.Component.dispatchEvent(Component.java:4713)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466)
at java.awt.Container.dispatchEventImpl(Container.java:2280)
at java.awt.Window.dispatchEventImpl(Window.java:2750)
--------------------------------------------------------------------
at java.awt.Component.dispatchEvent(Component.java:4713)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:709)
at java.awt.EventQueue$3.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:731)
at java.awt.EventQueue$4.run(EventQueue.java:729)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
java.lang.NullPointerException
at core.Owner.addCar(Owner.java:45)
at gui.GUI.intoMap1(GUI.java:36)
at gui.GUI.jButton1ActionPerformed(GUI.java:215)
at gui.GUI.access$100(GUI.java:17)
at gui.GUI$1.actionPerformed(GUI.java:87)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
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:6535)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
at java.awt.Component.processEvent(Component.java:6300)
at java.awt.Container.processEvent(Container.java:2236)
at java.awt.Component.dispatchEventImpl(Component.java:4891)
at java.awt.Container.dispatchEventImpl(Container.java:2294)
at java.awt.Component.dispatchEvent(Component.java:4713)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466)
at java.awt.Container.dispatchEventImpl(Container.java:2280)
at java.awt.Window.dispatchEventImpl(Window.java:2750)
at java.awt.Component.dispatchEvent(Component.java:4713)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:709)
at java.awt.EventQueue$3.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:731)
at java.awt.EventQueue$4.run(EventQueue.java:729)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
Car is created: regNum = B2
Exception in Owner when adding car
java.lang.NullPointerException
at core.Owner.addCar(Owner.java:34)
at gui.GUI.intoMap2(GUI.java:41)
at gui.GUI.jButton4ActionPerformed(GUI.java:230)
at gui.GUI.access$400(GUI.java:17)
at gui.GUI$4.actionPerformed(GUI.java:126)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
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:6535)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
at java.awt.Component.processEvent(Component.java:6300)
at java.awt.Container.processEvent(Container.java:2236)
at java.awt.Component.dispatchEventImpl(Component.java:4891)
at java.awt.Container.dispatchEventImpl(Container.java:2294)
at java.awt.Component.dispatchEvent(Component.java:4713)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466)
at java.awt.Container.dispatchEventImpl(Container.java:2280)
at java.awt.Window.dispatchEventImpl(Window.java:2750)
--------------------------------------------------------------------
at java.awt.Component.dispatchEvent(Component.java:4713)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:709)
at java.awt.EventQueue$3.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:731)
at java.awt.EventQueue$4.run(EventQueue.java:729)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
java.lang.NullPointerException
at core.Owner.addCar(Owner.java:45)
at gui.GUI.intoMap2(GUI.java:41)
at gui.GUI.jButton4ActionPerformed(GUI.java:230)
at gui.GUI.access$400(GUI.java:17)
at gui.GUI$4.actionPerformed(GUI.java:126)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
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:6535)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
at java.awt.Component.processEvent(Component.java:6300)
at java.awt.Container.processEvent(Container.java:2236)
at java.awt.Component.dispatchEventImpl(Component.java:4891)
at java.awt.Container.dispatchEventImpl(Container.java:2294)
at java.awt.Component.dispatchEvent(Component.java:4713)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466)
at java.awt.Container.dispatchEventImpl(Container.java:2280)
at java.awt.Window.dispatchEventImpl(Window.java:2750)
at java.awt.Component.dispatchEvent(Component.java:4713)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:709)
at java.awt.EventQueue$3.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:731)
at java.awt.EventQueue$4.run(EventQueue.java:729)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
CloseQuit executed
BUILD SUCCESSFUL (total time: 15 seconds)
第二次运行输出后：
g>2