Printing a list using reflection

问题:

 public class Service{ 
       String serviceName;
      //setter and getter
  }

  public class Version{ 
       int VersionID;
      //setter and getter
  }

  public void test(Object list){

        //it shd print the obtained list

   }

List< Service> list1; //Service is a Bean
List< Version> list2; //Version is a Bean
test(list1);
test(list2);

Now the test method shd print the obtained list - (i.e) If the list is of type Service ,then serviceName should be printed using its getter. If the list type is Version versionID should be printed.
Is it possible to achieve this without using Interface or abstract class?

回答1:

@danLeon has the simplest idea so far (adding toString to the classes), assuming you have access to Service and Version.

I'm not sure why you were thinking of reflection, but the only thing I can think of is that you want something that will work with any object that has a single attribute String getter, and then you would do something like this (crazy IMO, but it uses reflection):

Class clazz = list.get(0).getClass();
Method[] methods = clazz.getDeclaredMethods();
Method onlyStringGetter = null;
for (Method method: methods) {
    String mName = method.getName();
    if (mName.matches("get\w+") {
        if (method.getReturnType().equals(String.class) {
            if (onlyStringGetter != null) thrown new RuntimeException("More than one String getter available");
            onlyStringGetter = method;
        }
    }
}
if (onlyStringGetter == null) throw new RuntimeException("No String getter found for class: " + clazz.getName());
List<String> strings = new ArrayList<String>();
for (Object singleStringAttribObj: list) {
    // some exception handling needed for below
    String result = (String)onlyStringGetter.invoke(singleStringAttribObj);
    strings.add(result);
}
System.out.println(strings);

I haven't compiled or tried, but that is approximately right. Definitely some additional exception handling is required

回答2:

if(Object instanceof List) {
    List list = (List)Object ;

   for(int index=0; index < list.length();index++) {
       Object obj = list.get(index);

       if(obj instanceof Service) {
         //cast to service and print value or use reflection
           Service service= (Service)obj ;
           System.out.println(service.geServiceName());
       } else if(obj instanceof Version) {
          // cast to Version and print versionID  someting
          Version version = (Version)obj ;
          System.out.println(version.getVersionId());
     }
   }
}

回答3:

static public class Service {

    String serviceName;

    @Override
    public String toString() {
        return serviceName;
    }
}

static public class Version {

    String VersionID;

    @Override
    public String toString() {
        return VersionID;
    }
}

static public void test(List<?> list) {
    for (Object object : list) {
        System.out.println(object.toString());
    }
}

回答4:

public void test(Object list) {
    if(list instanceof List)
        test((List)list);
}

public void test(List<?> list) {
    if (!list.isEmpty()) {
        Object o = list.get(0);
        if (o instanceof Version) {
            @SuppressWarnings("unchecked")
            List<Version> lVersion = (List<Version>) list;
            for (Version v : lVersion) {
                System.out.println(v.getVersionID());
            }
        } else if (o instanceof Service) {
            @SuppressWarnings("unchecked")
            List<Service> lService = (List<Service>) list;
            for (Service s : lService) {
                System.out.println(s.getServiceName());
            }
        }
    }
}