那么Handler实现代码如下：
public class ConcreteHandler implements Handler{
private Handler successor;
public ConcreteHandler(Handler successor){
this.successor=successor;
}
public void handleRequest(Request request){
if (request instanceof HelpRequest){
//这里是处理Help的具体代码
}else if (request instanceof PrintRequst){
request.execute();
}else
//传递到下一个
successor.handle(request);
}
}
}
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