java - 检查 List包含哪种类型的对象

Question

List包含对象类型，但我需要检查该对象是否属于类型A或B：

A a = new A();
B b = new B();

List<A> aL = new ArrayList<A>();
List<B> bL = new ArrayList<B>();

如何检查是否List包含A对象或B对象？

这是代码：

    SegmentDetailInfo segmentDetailInfo  = new SegmentDetailInfo();
    segmentDetailInfo.setSeg_Id("1");

    SegReqInfoBean segReqInfoBean  = new SegReqInfoBean();
    segReqInfoBean.setPageName("homepage");

    List<SegmentDetailInfo> rhsList1 = new ArrayList<SegmentDetailInfo>();
    rhsList1.add(segmentDetailInfo);

    List<SegReqInfoBean> rhsList2 = new ArrayList<SegReqInfoBean>();
    rhsList2.add(segReqInfoBean);

    doProspecListCompareCheck(rhsList1);
    doProspecListCompareCheck(rhsList2);

}

private static void doProspecListCompareCheck(Object rhsList) {
     if (rhsList instanceof List<SegmentDetailInfo>) //wrong Check
         //DoTHIS
     else if(rhsList instanceof List<SegReqInfoBean>)   //wrong Check       
         //Do THIS       

}

==================================================== ======

    SegmentDetailInfo segmentDetailInfo  = new SegmentDetailInfo();
    segmentDetailInfo.setSeg_Id("1");

    SegReqInfoBean segReqInfoBean1  = new SegReqInfoBean();
    segReqInfoBean1.setPageName("Home");

    List<SegmentDetailInfo> rhsList1 = new ArrayList<SegmentDetailInfo>();
    rhsList1.add(segmentDetailInfo);

    List<SegReqInfoBean> rhsList2 = new ArrayList<SegReqInfoBean>();      
    rhsList2.add(segReqInfoBean1);

    String Homepage="homepage";

    doProspecListCompareCheck(Homepage);
    doProspecListCompareCheck(rhsList2);
    doProspecListCompareCheck(rhsList2);


private static void doProspecListCompareCheck(Object rhsListObj) {
         List<String> rhsStrList = new ArrayList<String>();
         List<SegReqInfoBean> segReqInfoBeanList = new ArrayList<SegReqInfoBean>();
         List<SegmentDetailInfo> segmentDetailInfoList = new ArrayList<SegmentDetailInfo>();


     if (rhsListObj != null && rhsListObj instanceof List) {

         if (((List<SegmentDetailInfo>) rhsListObj).get(0) instanceof SegmentDetailInfo){

                System.out.println("SegmentDetailInfo loading");
                segmentDetailInfoList = (List<SegmentDetailInfo>) rhsListObj;     
        }
         else if(((List<SegReqInfoBean>) rhsListObj).get(0) instanceof SegReqInfoBean){

                System.out.println("SegReqInfoBean loading");   
                segReqInfoBeanList = (List<SegReqInfoBean>) rhsListObj;
         }          

     }else if ( rhsListObj != null && rhsListObj instanceof String) {

         rhsStrList.add(rhsListObj.toString());

     }

}

score 25 · Accepted Answer

您可以做到这一点的一种方法是先Object在以下内容中进行比较List：

private static void doProspecListCompareCheck(List rhsList)
{
    if(rhsList != null && !rhsList.isEmpty())
    {
        if (rhsList.get(0) instanceof SegReqInfoBean)
        {

        }
        else if(rhsList.get(0) instanceof SegmentDetailInfo)    
        {

        }
    }
}

score 9 · Accepted Answer

泛型仅提供编译时检查。在运行时，它们完全消失了。这称为类型擦除。所以在运行时，您的代码如下所示：

    List rhsList1 = new ArrayList();
    rhsList1.add(segmentDetailInfo);

    List rhsList2 = new ArrayList();
    rhsList2.add(segReqInfoBean);

    doProspecListCompareCheck(rhsList1);
    doProspecListCompareCheck(rhsList2);

}
private static void doProspecListCompareCheck(Object rhsList) {


     if (rhsList instanceof List) //wrong Check
         //DoTHIS
     else if(rhsList instanceof List)   //wrong Check       
         //Do THIS       

}

通过泛型参数区分两个泛型对象在 Java 中根本无法做到。

score 0 · Accepted Answer

如果您知道列表非空，您可以执行 rhsList.get(0) instanceof SegReqInfobean

如果列表可能为空，您可以从插入正确类型的对象开始，然后记住索引 0 存储了一个虚拟对象，因此在处理之前将其删除（或者只是开始处理索引 0 处的列表）。泛型只是编译时的便利。正如您所发现的，您不能在运行时使用泛型类型。

score 0 · Accepted Answer

for (Object aList : list) {
    Class cls = aList.getClass();
    System.out.println("The type of the object is: " + cls.getName());
}

这似乎对我有用。这不仅会检测任何索引是否属于 A 或 B 类型，还会检测每种类型。

java - 检查 List包含哪种类型的对象

4 回答 4

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