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;
}

Lena Bru · Accepted Answer · 2014-05-25 08:28:42Z

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, 2014 at 8:28

Lena Bru

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7 Comments

PakkuDon Over a year ago

Are you sure that u.getAllPermissions() returns something that can be cast to List<String>?

Lena Bru Over a year ago

PermissionUser seems to be a custom class, so this is up to the composer of this question. He claims that it does

Lena Bru Over a year ago

If it can't be, the next error he'll get will be class cast exception

Lena Bru Over a year ago

Please rephrase your comment, as i have not downvoted anybody, i don't understand what you mean

Maroun Over a year ago

@LenaBru Misunderstood you :) Now after you've explained your answer, you get my +1.

|

Aviad · Accepted Answer · 2014-05-25 08:36:59Z

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, 2014 at 8:36

Aviad

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1 Comment

rainversion_3 Over a year ago

Casting it to Object works but if we had List<Foo> instead of List<String> we will loose the ability to call methods available on Foo object inside the for loop

arsalan Yaghoubi · Accepted Answer · 2022-07-17 00:22:05Z

0

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.

answered Jul 17, 2022 at 0:22

arsalan Yaghoubi

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