抽象语法-智能科学与人工智能.PPT

* * * * * * * * * * * * * * * * * * * * * * * * * The aglet class is the key class in the Aglet API. It is the abstract class that aglet developer can use as base class when creating customized aglets. The aglet class defines methods for controlling its own life cycle: methods for cloning, dispatching, deactivating ,and disposing of itself. It also defines methods that are supposed to be overridden by programmer in order to customize the aglet’s behavior. These methods are systematically invoked by the system when certain events take place—remember that aglet programming model is event-based. Now look at some methods in aglet class. First we start with importing the aglet package, and then define the MyFirstAglet class, which inherits from the Aglet class. For example, we want our aglet to perform some specific initialization when it is created, we can override the “onCreation” method. When an aglet has been created or when it arrives in a new context, it’s given its own thread of execution through a system invocation of its “run” method. We can look on this invocation as a means of giving the aglet a degree of autonomy. The run method is called every time when an aglet arrives at or is activated in a new context, you can say it becomes the main entry point for the aglet’s thread of execution. By overriding this method, we can customize the aglet’s autonomous behavior. For example, we want the aglet to dispatch itself to a remote context, then we can call the dispatch method, with the URL of the remote host as the argument. This URL should specify the host and domain names of the destination context and the protocol(atp) to be used for transferring the aglet over network. URL can also include the name of the remote context. If no context name specified, it will move into the default context. * What happens to aglet when dispatch() is called? Basically the aglet will disappear from your machine and will reappear in the same object state at the specified destinat