Java - Casting List<Object> to List<Entity>

Question

I'm trying to cast a list of Objects to a list of my own class type. So far what I'm doing is:

List<Company> companies = (List<Company>)(Object) repository.findAllCompanyNames();

repository.findAllCompanyNames() is returning a List<Object>

My Company class looks like:

public class Company {

    public Company(){}

    public Company(int id, String name){
        this.id = id;
        this.name = name;
    }

    public int id;
    public String name;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

I don't get any error the problem is the value of companies after the cast, it is:

companies = {ArrayList@11743}  size = 4
 0 = {Object[2]@11753} 
  0 = {Integer@11761} "1"
  1 = "Company 1"
 1 = {Object[2]@11754} 
  0 = {Integer@11785} "3"
  1 = "Company 3"
 2 = {Object[2]@11755} 
  0 = {Integer@11779} "4"
  1 = "Company TT"
 3 = {Object[2]@11756} 
  0 = {Integer@11764} "5"
  1 = "Company 34"
 4 = {Object[2]@11757}

and I think the companies list should contain Company objects like:

- Id: 1
- Name: Company 1
- etc ..

Any idea what it's going on?

but, from what is shown there, it does contain it? you´re just printing the additional hashcode from the class itself and the one from the List. — SomeJavaGuy
– SomeJavaGuy, Commented Mar 7, 2017 at 11:25
What is your repository.findAllCompanyNames actually returning? If it isn't returning a Company casting doesn't change a thing. — M. Deinum
– M. Deinum, Commented Mar 7, 2017 at 11:26
@JonSkeet what is the right way to change the object? I thought casting the list would change as well the object :S — gon250
– gon250, Commented Mar 7, 2017 at 11:27
If casting would change the object, then every problem could be solved with this magic line mySolutions = (List<Solutions>)(Object) myProblems; // if only — Patrick Parker
– Patrick Parker, Commented Mar 7, 2017 at 11:35

Kayaman · Accepted Answer · 2017-03-07 11:26:34Z

4

No, the list shouldn't contain Company objects because you're not retrieving companies, but their names. The method is called findAllCompanyNames() and it returns a List<Object[]> (runtime type), with each element containing (presumably) the company id and the company name.

If you show the repository class, it should be more obvious and you'll probably find a method that returns the company objects you want.

answered Mar 7, 2017 at 11:26

Kayaman

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Anton Balaniuc · Accepted Answer · 2017-03-07 12:18:06Z

0

Are you able to use java-8? You can just transform a List<Object[]> into a List<Company> using stream:

List<Object[]> companies = Arrays.asList(
            new Object[]{1, "Company nam 1"}, 
            new Object[]{2, "Company nam 2"}
);

now we can convert companies to a List<Company>:

List<Company> companyList = companies.stream().map(
               o -> new Company((Integer) o[0], (String) o[1])
).collect(Collectors.toList());

I hope this helps.

answered Mar 7, 2017 at 12:18

Anton Balaniuc

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