Java - Type mismatch: cannot convert from element type Object to String

Question

I'm having this error:

Type mismatch: cannot convert from element type Object to String

This is the code in error:

public List<String> customPrefixes(PermissionUser u)
{
    List returnlist = new ArrayList();
    for (String k : u.getAllPermissions().keySet()) {
        List perms = (List)u.getAllPermissions().get(k);
        for (String s : perms) {
            String[] split = s.split(".");
            if ((split.length >= 3) && 
              (split[0].equalsIgnoreCase("plugin")) && 
              (split[1].equalsIgnoreCase("prefix"))) {
                returnlist.add(split[2]);
            }
        }
    }
    return returnlist;
}

score 11 · Accepted Answer · answered May 25 '14 at 08:28

11

try this :

public List<String> customPrefixes(PermissionUser u)
  {
    List<String> returnlist = new ArrayList<String>();
    for (String k : u.getAllPermissions().keySet()) {
      List<String> perms = (List<String>)(u.getAllPermissions()).get(k);
      for (String s : perms) {
        String[] split = s.split(".");
        if ((split.length >= 3) &&
          (split[0].equalsIgnoreCase("plugin")) &&
          (split[1].equalsIgnoreCase("prefix"))) {
          returnlist.add(split[2]);
        }
      }

    }

    return returnlist;
  }

You were missing "<String>" in the List declaration

answered May 25 '14 at 08:28

Lena Bru

13,521
11
61
126

Are you sure that `u.getAllPermissions()` returns something that can be cast to `List`? – PakkuDon May 25 '14 at 08:31
PermissionUser seems to be a custom class, so this is up to the composer of this question. He claims that it does – Lena Bru May 25 '14 at 08:33
If it can't be, the next error he'll get will be class cast exception – Lena Bru May 25 '14 at 08:34
Please rephrase your comment, as i have not downvoted anybody, i don't understand what you mean – Lena Bru May 25 '14 at 08:40
Thank you, @LenaBru I feel so dumb about forgetting about the . (facepalm). Correct answer. – PlayinCOD3142 May 25 '14 at 08:40
1

@LenaBru Misunderstood you :) Now after you've explained your answer, you get my +1. – Maroun May 25 '14 at 08:41
@PlayinCODMC make note i put brackets on (u.getAllPermissions) as i want to cast the getAllPermissions return type, and not u – Lena Bru May 25 '14 at 08:44

score 1 · Answer 2 · answered May 25 '14 at 08:36

1

I think you're casting is wrong..

What is u.getAllPermissions().get(k); should return? List of something? if it does so you need to add type of the generic list

List<String> perms = (List<String>)u.getAllPermissions().get(k);

If that doesn't work you can also try to do

for (Object o : perms) {
 String s = o.toString();
 .....
}

Hope that helps.. If not answer my question and it will be easier to help

answered May 25 '14 at 08:36

Aviad

1,539
1
9
24

Casting it to `Object` works but if we had `List` instead of `List` we will loose the ability to call methods available on `Foo` object inside the for loop – rainversion_3 Oct 16 '19 at 13:19

score 0 · Answer 3 · answered Jul 17 '22 at 00:22

Another reason for this error can be the way you have initialized your container; as a case in point; you have initialize list2 as below:

List list2 = new ArrayList <Integer>();

instead of

List<Integer> list2 = new ArrayList <Integer>();

So, you are looping over a wrong type of container ( if we can call this a container) as below :

for(Integer x:list2){
            System.out.println(x);
        }

Thus, you need to revise the way you have initialize your container ( here is a list) and there is no problem with your datatype, etc.

Java - Type mismatch: cannot convert from element type Object to String

3 Answers3

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