java - 我的 Facade :( 中的空指针

Question

我写了一个任务管理器，好吧；说来话长……顺便说一句，全部用 Java 编写。所以我写了一个门面，你可以在下面看到 HashMap 有问题，我怀疑我在构建过程中尝试添加到 HashMap 中的值不太顺利。触发空指针异常的方法是 create 方法。该方法的输入参数已经过我和我可信赖的调试器的验证。

这里的任何帮助都会很棒...我确定我忘了提及一些事情，所以我会尽快回复评论，因为我现在需要完成这件事。

package persistence;

import java.util.UUID;
import java.util.HashMap;

import persistence.framework.ComplexTaskRDBMapper;
import persistence.framework.IMapper;
import persistence.framework.RepeatingTaskRDBMapper;
import persistence.framework.SingleTaskRDBMapper;

public class PersistanceFacade {

    @SuppressWarnings("unchecked")
    private static Class SingleTask;
    @SuppressWarnings("unchecked")
    private static Class RepeatingTask;
    @SuppressWarnings("unchecked")
    private static Class ComplexTask;

    private static PersistanceFacade uniqueInstance = null;
    @SuppressWarnings("unchecked")
    private HashMap<Class, IMapper> mappers;

    public PersistanceFacade() {
        mappers = new HashMap<Class, IMapper>();
        try {
            SingleTask = Class.forName("SingleTask");
            RepeatingTask = Class.forName("RepeatingTask");
            ComplexTask = Class.forName("ComplexTask");
            mappers.put(SingleTask, new SingleTaskRDBMapper());
            mappers.put(RepeatingTask, new RepeatingTaskRDBMapper());
            mappers.put(ComplexTask, new ComplexTaskRDBMapper());
        }
        catch (ClassNotFoundException e) {}

    }

    public static synchronized PersistanceFacade getUniqueInstance() {
        if (uniqueInstance == null) {
            uniqueInstance = new PersistanceFacade();
            return uniqueInstance;
        }
        else return uniqueInstance;
    }

    public void create(UUID oid, Object obj) {
        IMapper mapper = (IMapper) mappers.get(obj.getClass());
        mapper.create(oid, obj);
    }

    @SuppressWarnings("unchecked")
    public Object read(UUID oid, Class type) {
        IMapper mapper = (IMapper) mappers.get(type);
        return mapper.read(oid);
    }

    public void update(UUID oid, Object obj) {
        IMapper mapper = (IMapper) mappers.get(obj.getClass());
        mapper.update(oid, obj);
    }

    @SuppressWarnings("unchecked")
    public void destroy(UUID oid, Class type) {
        IMapper mapper = (IMapper) mappers.get(type);
        mapper.destroy(oid);
    }


}

Answer 1

要使 Class.forName("RepeatingTask") 返回一个类，您必须有一个类 persistence.RepeatingTask。但是在您的评论中，您说 obj.getClass() 返回 domain.RepeatingTask 所以在我看来您有 2 个“RepeatingTask”类或 domain.RepeatingTask 是一个子类型。