在将扩展加载到程序中时,我遇到了一个主要问题。我得到一个例外,因为没有有效的构造函数。
问题出在行中:
ekstensja = (ArrayList<Dydaktyk>) ois.readObject();
我得到这样的东西:
java.io.InvalidClassException: Dydaktyk; no valid constructor
at java.io.ObjectStreamClass$ExceptionInfo.newInvalidClassException(Unknown Source)
at java.io.ObjectStreamClass.checkDeserialize(Unknown Source)
at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.readObject(Unknown Source)
at java.util.ArrayList.readObject(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at java.io.ObjectStreamClass.invokeReadObject(Unknown Source)
at java.io.ObjectInputStream.readSerialData(Unknown Source)
at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.readObject(Unknown Source)
at Dydaktyk.wczytajEkstensje(Dydaktyk.java:81)
at Dydaktyk.<clinit>(Dydaktyk.java:69)
at java.io.ObjectStreamClass.hasStaticInitializer(Native Method)
at java.io.ObjectStreamClass.computeDefaultSUID(Unknown Source)
at java.io.ObjectStreamClass.access$100(Unknown Source)
at java.io.ObjectStreamClass$1.run(Unknown Source)
at java.io.ObjectStreamClass$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.io.ObjectStreamClass.getSerialVersionUID(Unknown Source)
at java.io.ObjectStreamClass.initNonProxy(Unknown Source)
at java.io.ObjectInputStream.readNonProxyDesc(Unknown Source)
at java.io.ObjectInputStream.readClassDesc(Unknown Source)
at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.defaultReadFields(Unknown Source)
at java.io.ObjectInputStream.readSerialData(Unknown Source)
at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.readObject(Unknown Source)
at java.util.ArrayList.readObject(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at java.io.ObjectStreamClass.invokeReadObject(Unknown Source)
at java.io.ObjectInputStream.readSerialData(Unknown Source)
at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.defaultReadFields(Unknown Source)
at java.io.ObjectInputStream.readSerialData(Unknown Source)
at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.readObject(Unknown Source)
at java.util.ArrayList.readObject(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at java.io.ObjectStreamClass.invokeReadObject(Unknown Source)
at java.io.ObjectInputStream.readSerialData(Unknown Source)
at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.readObject(Unknown Source)
at Przedmiot.wczytajEkstensje(Przedmiot.java:99)
at Przedmiot.<clinit>(Przedmiot.java:87)
at GUI.main(GUI.java:100)
static {
wczytajEkstensje(); // load Extension
}
public static void wczytajEkstensje() {// load extension
FileInputStream fis = null;
ObjectInputStream ois = null;
try {
fis = new FileInputStream("dydaktyk.ser");
ois = new ObjectInputStream(fis);
// here is the problem
ekstensja = (ArrayList<Dydaktyk>) ois.readObject();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
} finally {
try {
if (ois != null) {
ois.close();
}
} catch (IOException e) {
}
try {
if (fis != null) {
fis.close();
}
} catch (IOException e) {
}
}
}
public static void zapiszEkstensje() {// save extension
FileOutputStream fos = null;
ObjectOutputStream oos = null;
try {
fos = new FileOutputStream("dydaktyk.ser");
oos = new ObjectOutputStream(fos);
oos.writeObject(ekstensja); // serialization
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (oos != null) {
oos.close();
}
} catch (IOException e) {
}
try {
if (fos != null) {
fos.close();
}
} catch (IOException e) {
}
}
}
类< code>Dydaktyk应该有一个可访问的(公共的或受保护的)无参数构造函数,以便序列化反射机制可以创建该类的实例:
public Dydaktyk() {
...
}
来自文档
在反序列化期间,将使用类的公共或受保护的无参数构造函数初始化不可序列化类的字段。无参数构造函数必须可用于可序列化的子类。可序列化子类的字段将从流中恢复。
如Oracle站点中关于Serialization
接口的规定:
在反序列化期间,将使用类的公共或受保护的无参数构造函数初始化不可序列化类的字段。无参数构造函数必须可用于可序列化的子类。可序列化子类的字段将从流中恢复。
我猜Dydaktyk
是某个类的子类。您已经在超类
中定义了参数构造函数
,但没有在其中定义无参数构造函数
。编译器没有为该超类
插入默认构造函数。因此,您也应该在超类中定义一个无参数构造函数
。