检查哪种类型的对象List<?>.包含 [英] Check which type of object List<?> contains

问题描述

List包含对象类型，但是我需要检查该对象的类型是否为A或B:

List contains the object type, but I need to check if that object is of type A or 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List包含A个对象还是B个对象?

How can I check whether List contains A objects or B objects?

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());

     }

}

推荐答案

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.因此，在运行时，您的代码如下所示:

Generics only provide compile-time checks. At runtime, they are completely gone. This is known as type erasure. So at runtime, your code looks like this:

    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       

}

用Java的泛型参数来区分两个泛型对象根本不是您所能做的.

Distinguishing two generic objects by their generic parameter is simply not something you can do in Java.

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