Finding the specific type held in an ArrayList<Object> (ie. Object = String, etc.)

Posted by Christopher Griffith on Stack Overflow See other posts from Stack Overflow or by Christopher Griffith
Published on 2011-11-16T01:46:43Z Indexed on 2011/11/16 1:50 UTC
Read the original article Hit count: 144

Filed under:

java

|

generics

|

casting

Say I have an ArrayList that I have cast to an ArrayList of objects. I know that all the objects that were in the ArrayList I cast were of the same type, but not what the type was.

Now, if the ArrayList is not empty, I could take one of the objects in it and use the instanceof operator to learn what the actual type is. But what of the case where the ArrayList is empty? How do I determine what type Object actually is then? Is it possible?

© Stack Overflow or respective owner

Related posts about java

Tomcat 6: Access Control Exception?

as seen on Server Fault - Search for 'Server Fault'
I'm trying to setup a tomcat6 server, and I'm trying to match another setup someone else established. However, my deployment (default Ubuntu install) uses a policy.d/ directory structure, and the established server just uses a catalina.policy file. I've tried setting every entry in policy.d to match… >>> More
Problem in creation MDB Queue connection at Jboss StartUp

as seen on Stack Overflow - Search for 'Stack Overflow'
I am not able to create a Queue connection in JBOSS4.2.3GA Version & Java1.5, as I am using MDB as per the below details. I am putting this MDB in a jar file(named utsJar.jar) and copied it in deploy folder of JBOSS, In the test env. this MDB works well but in another env. [ env settings and… >>> More
failing to establish connection between Postgres db and gwt

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi, I am using Postgres and gwt 2.0 for one of my applications. I am facing problem connecting to the database. When I try to connect it gives "ClassNotFoundException". Here is what I get when I try to connect to database: java.lang.ClassNotFoundException: org.postgresql.Driver at java.net… >>> More
failing to establish connection between postgre db and gwt

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi, For i am using postgre and gwt 2.0 for one of my applications. I am facing problem connecting to the database. When i try to connect it gives "ClassNotFoundException". Here is what i get when i try to connect to database: java.lang.ClassNotFoundException: org.postgresql.Driver at java.net… >>> More
Migration and deployement problems JBoss 4.2.2.GA to JBoss 6.0.0.M2

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi, I'm trying to migrate an application running on JBoss 4.2.2.GA to JBoss 6.0.0.M2 I give you some log to explain my problem : boot.log : 2010-03-16 09:59:29,406 ERROR [org.jboss.system.server.profileservice.ProfileServiceBootstrap] (Thread-2) Failed to load profile: Summary of incomplete deployments… >>> More

Related posts about generics

Java generics: What is the compiler's issue here?

as seen on Stack Overflow - Search for 'Stack Overflow'
I have the following methods: public <T> T fromJson( Reader jsonData, Class<T> clazz ) { return fromJson( jsonData, (Type)clazz ); } public <T> T fromJson( Reader jsonData, Type clazz ) { ... } The compiler is saying about the first method: type parameters of <T>T… >>> More
Why does NUnit ignore datapoints when using generics in a theory

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm trying to make use of the TheoryAttribute, introduced in NUnit 2.5. Everything works fine as long as the arguments are of a defined type: [Datapoint] public double[,] Array2X2 = new double[,] { { 1, 0 }, { 0, 1 } }; [Theory] public void TestForArbitraryArray(double[,] array) { // ... } It… >>> More
Instantiating generics type in java

as seen on Stack Overflow - Search for 'Stack Overflow'
I would like to create an object of Generics Type in java. Please suggest how can I achieve the same. suppose I have the class declaration as: public class Abc<T> { public static void main(String[] args) { // I want to create an instance of T } } >>> More
.NET converting simple arrays to List Generics

as seen on Stack Overflow - Search for 'Stack Overflow'
This question might seem trivial and also stupid at the first glance, but it is much more than this. I have an array of any type T (T[]) and I want to convert it into a List generic (List<T>). Is there any other way apart from creating a Generic list, traversing the whole array and adding the… >>> More
Instantiating a list of parameterized types, making beter use of Generics and Linq

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm hashing a file with one or more hash algorithms. When I tried to parametrize which hash types I want, it got a lot messier than I was hoping. I think I'm missing a chance to make better use of generics or LINQ. I also don't like that I have to use a Type[] as the parameter instead of limiting… >>> More