1. A detection device for detecting a plurality of classes of object data, wherein the plurality of classes are merged step-by-step into a predetermined multilayer structure according to a similarity criterion and arranged at a bottom layer as the most finely classified classes, the detection device comprising: an input circuit configured to input data to be detected; and a processor configured to execute a cascade classifier comprising a plurality of level classifiers connected in series, the plurality of level classifiers configured to perform a classification respectively on the classes at respective layers in the predetermined multilayer structure according to a from-coarse-to-fine policy, and each of the level classifiers comprising strong classifiers, a number of which corresponds to a number of the classes being classified, wherein each of the strong classifiers comprises a group of weak classifiers, and each of the weak classifiers is configured to perform a weak classification on the data to be detected using a feature, each of the level classifiers comprises a shared features list, each feature in the shared features list is shared by one or more weak classifiers respectively belonging to different strong classifiers, and the weak classifiers using a same feature and belonging to different strong classifiers have parameter values different from one another, and the cascade classifier is configured to subject the data to be detected sequentially to judgment by each of the strong classifiers in each of the level classifiers so that when the data to be detected is judged by one of the strong classifiers of a level classifier as non-object data, the data to be detected is precluded from judgment by the other strong classifiers of the level classifier and sub-classes in the subsequent level classifiers, judge, for each of the level classifiers, whether there is a feature in the shared features list that is correlated only with the respective strong classifiers precluded from the judgment, and label the feature, when the cascade classifier judges that the feature is correlated only with the respective strong classifiers precluded from the judgment, as an invalid feature for which no feature value is further calculated.