java - Java从HashSet中获取特定的类对象

Question

我有一个 public Set<ProjectItem> projectItems = new HashSet<ProjectItem>();它可以包含两种类型的类( ProjectItem 是它们的抽象父类(super class))。这些类(class)是 Deliverable和 Task .我想获得 Deliverable 类的所有对象来自 Set .因此我这样写:

public Set<Deliverable> allDeliverables(){
Set<Deliverable> result = new HashSet<Deliverable>();
for(Iterator<ProjectItem> iter = projectItems.iterator(); iter.hasNext(); iter.next()){
    if (iter.next().getClass() == Deliverable.class){
    Deliverable del = (Deliverable) iter.next();
    result.add(del);
    }
}
return result;
}

但这是个异常(exception)——

Exception in thread "main" java.lang.ClassCastException: edu.Chryb.ProjectManagement.Task cannot be cast to edu.Chryb.ProjectManagement.Deliverable

符合:Deliverable del = (Deliverable) iter.next();

if 查询中是否有错误？

感谢您的帮助。

Answer 1

您的代码有点过时了。尝试:

for(Iterator<ProjectItem> iter = projectItems.iterator(); iter.hasNext(); iter.next()){
    ProjectItem item = iter.next();
    if (item.getClass() == Deliverable.class){
        result.add((Deliverable)item);
    }
}