Examples of java.io.Serializable

java.io.Serializable
Serializability of a class is enabled by the class implementing the java.io.Serializable interface. Classes that do not implement this interface will not have any of their state serialized or deserialized. All subtypes of a serializable class are themselves serializable. The serialization interface has no methods or fields and serves only to identify the semantics of being serializable.
To allow subtypes of non-serializable classes to be serialized, the subtype may assume responsibility for saving and restoring the state of the supertype's public, protected, and (if accessible) package fields. The subtype may assume this responsibility only if the class it extends has an accessible no-arg constructor to initialize the class's state. It is an error to declare a class Serializable if this is not the case. The error will be detected at runtime.
During deserialization, the fields of non-serializable classes will be initialized using the public or protected no-arg constructor of the class. A no-arg constructor must be accessible to the subclass that is serializable. The fields of serializable subclasses will be restored from the stream.
When traversing a graph, an object may be encountered that does not support the Serializable interface. In this case the NotSerializableException will be thrown and will identify the class of the non-serializable object.
Classes that require special handling during the serialization and deserialization process must implement special methods with these exact signatures:
```
 private void writeObject(java.io.ObjectOutputStream out) throws IOException private void readObject(java.io.ObjectInputStream in) throws IOException, ClassNotFoundException; private void readObjectNoData()  throws ObjectStreamException; 
```
The writeObject method is responsible for writing the state of the object for its particular class so that the corresponding readObject method can restore it. The default mechanism for saving the Object's fields can be invoked by calling out.defaultWriteObject. The method does not need to concern itself with the state belonging to its superclasses or subclasses. State is saved by writing the individual fields to the ObjectOutputStream using the writeObject method or by using the methods for primitive data types supported by DataOutput.
The readObject method is responsible for reading from the stream and restoring the classes fields. It may call in.defaultReadObject to invoke the default mechanism for restoring the object's non-static and non-transient fields. The defaultReadObject method uses information in the stream to assign the fields of the object saved in the stream with the correspondingly named fields in the current object. This handles the case when the class has evolved to add new fields. The method does not need to concern itself with the state belonging to its superclasses or subclasses. State is saved by writing the individual fields to the ObjectOutputStream using the writeObject method or by using the methods for primitive data types supported by DataOutput.
The readObjectNoData method is responsible for initializing the state of the object for its particular class in the event that the serialization stream does not list the given class as a superclass of the object being deserialized. This may occur in cases where the receiving party uses a different version of the deserialized instance's class than the sending party, and the receiver's version extends classes that are not extended by the sender's version. This may also occur if the serialization stream has been tampered; hence, readObjectNoData is useful for initializing deserialized objects properly despite a "hostile" or incomplete source stream.
Serializable classes that need to designate an alternative object to be used when writing an object to the stream should implement this special method with the exact signature:
```
 ANY-ACCESS-MODIFIER Object writeReplace() throws ObjectStreamException; 
```
This writeReplace method is invoked by serialization if the method exists and it would be accessible from a method defined within the class of the object being serialized. Thus, the method can have private, protected and package-private access. Subclass access to this method follows java accessibility rules.
Classes that need to designate a replacement when an instance of it is read from the stream should implement this special method with the exact signature.
```
 ANY-ACCESS-MODIFIER Object readResolve() throws ObjectStreamException; 
```
This readResolve method follows the same invocation rules and accessibility rules as writeReplace.
The serialization runtime associates with each serializable class a version number, called a serialVersionUID, which is used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible with respect to serialization. If the receiver has loaded a class for the object that has a different serialVersionUID than that of the corresponding sender's class, then deserialization will result in an {@link InvalidClassException}. A serializable class can declare its own serialVersionUID explicitly by declaring a field named "serialVersionUID" that must be static, final, and of type long:
```
 ANY-ACCESS-MODIFIER static final long serialVersionUID = 42L; 
```
If a serializable class does not explicitly declare a serialVersionUID, then the serialization runtime will calculate a default serialVersionUID value for that class based on various aspects of the class, as described in the Java(TM) Object Serialization Specification. However, it is strongly recommended that all serializable classes explicitly declare serialVersionUID values, since the default serialVersionUID computation is highly sensitive to class details that may vary depending on compiler implementations, and can thus result in unexpected InvalidClassExceptions during deserialization. Therefore, to guarantee a consistent serialVersionUID value across different java compiler implementations, a serializable class must declare an explicit serialVersionUID value. It is also strongly advised that explicit serialVersionUID declarations use the private modifier where possible, since such declarations apply only to the immediately declaring class--serialVersionUID fields are not useful as inherited members. Array classes cannot declare an explicit serialVersionUID, so they always have the default computed value, but the requirement for matching serialVersionUID values is waived for array classes. @author unascribed @version 1.25, 11/17/05 @see java.io.ObjectOutputStream @see java.io.ObjectInputStream @see java.io.ObjectOutput @see java.io.ObjectInput @see java.io.Externalizable @since JDK1.1


  private void receivedMessage(Object packet) {
    log.log(Level.FINE, "reading packet"); //$NON-NLS-1$ 
        if (packet instanceof Message) {
          Message messagePacket = (Message)packet;
          Serializable messageKey = messagePacket.getMessageKey();
            log.log(Level.FINE, "read asynch message:" + messageKey); //$NON-NLS-1$ 
            ResultsReceiver<Object> listener = asynchronousListeners.remove(messageKey);
            if (listener != null) {
                listener.receiveResults(messagePacket.getContents());
            }

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     @param timeout Max number of msecs until the call returns - if timeout elapses
     null will be returned
     @param max_tries Max number of attempts to fetch the cache from the coordinator (will be set to 1 if < 1)
     */
    public Serializable getCacheFromMember(Address mbr, long timeout, int max_tries) {
        Serializable cache=null;
        int num_tries=0;
        Info info;
        Message msg;
        Address dst=mbr;  // member from which to fetch the cache

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        return v != null ? (Address) v.elementAt(0) : null;
    }




    void handleCacheRequest(Address sender) throws ChannelException {
        Serializable cache=null;
        Message msg;
        Info info;


        if(sender == null) {
            // +++ remove

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        return _sched;
    }


    public <T extends Serializable> T execute(Request request, ReturnType returnType) throws RemoteException {
        assert (_sched != null);
        final Serializable result;
        final int sign = request.getSignature();
        switch (sign) {
            case QueryRequest.SIGNATURE:
                final String query = ((QueryRequest) request).getQuery();
                BackendProcessor proc = _sched.dispatchRequest(request);

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    }




    public void _set(String fqn, Serializable element) {
        Node n;
        Serializable old_el=null;


        if(fqn == null || element == null) return;
        n=findNode(fqn);
        if(n == null) {
            if(log.isErrorEnabled()) log.error("node " + fqn + " not found");

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    }


    /** similar to set, but does not error if node does not exist, but rather does an add instead */
    public void _reset(String fqn, Serializable element) {
        Node n;
        Serializable old_el=null;


        if(fqn == null || element == null) return;
        n=findNode(fqn);
        if(n == null) {
            _add(fqn, element);

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        if ( taskData.getDocumentAccessType() == AccessType.Inline ) {
            content = em.find( Content.class,
                               taskData.getDocumentContentId() );
        }
        ExpressionCompiler compiler = new ExpressionCompiler( new String( content.getContent() ) );
        Serializable expr = compiler.compile();
        Object object = MVEL.executeExpression( expr );
        
        Map<String, Object> vars = new HashMap<String, Object>();
        vars.put( docVar, object );
        // for now will have to assume the recipient is a User, we need to figure out if Groups have an alias

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      pconf.addPackageImport("java.util");
      for(String entry : getInputs().keySet()){
        pconf.addImport(entry, getInputs().get(entry));
        }
      ParserContext context = new ParserContext(pconf);
        Serializable s = MVEL.compileExpression(str.trim(), context);
        return MVEL.executeExpression(s, vars);
    }

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            simpleValueSupport.setValue(null);
            return;
        }
        // String value is non-null, so we can massage it into the proper type for the SimpleMetaValue's inner value.
        SimpleMetaType simpleMetaType = simpleValueSupport.getMetaType();
        Serializable innerValue;
        if (simpleMetaType.equals(SimpleMetaType.STRING) || simpleMetaType.equals(SimpleMetaType.NAMEDOBJECT))
            innerValue = propSimpleValue;
        else if (simpleMetaType.equals(SimpleMetaType.BOOLEAN) || simpleMetaType.equals(SimpleMetaType.BOOLEAN_PRIMITIVE))
            innerValue = Boolean.valueOf(propSimpleValue);
        else if (simpleMetaType.equals(SimpleMetaType.BYTE) || simpleMetaType.equals(SimpleMetaType.BYTE_PRIMITIVE))

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      return context.getVdbName();
    }


    // ================= Function - COMMANDPAYLOAD ========================
    public static Object commandPayload(CommandContext context) {
        Serializable payload = context.getCommandPayload();
        if(payload == null) {
            return null;
        }
        // 0-arg form - just return payload as a string if it exists
        return payload.toString();
    }

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