Converting List<ArrayList> to String[]

Question

I have a

List<ArrayList> arg = new ArrayList<ArrayList>();

with

[[logo], [cd_branche], [lib_branche]],

(other arguments not relevant) 

[[1111,22222,3333]],[[2222,324,432]]...

and I want to cast it to a String[] so I did this

    Object[] obj = arg.toArray();
    String[] headers =new String[obj.length];

    for(int i=0;i<headers.length;i++) { 
        headers[i]= (String) obj[i]; 
        }

but I'm getting

java.util.ArrayList cannot be cast to java.lang.String

The output I'm looking for is

headers[0]=logo
headers[1]=cd_branche
headers[2]=lib_branche

Using Java 6

Ori Lentz · Accepted Answer · 2015-08-13 14:43:50Z

1

It sounds like you want it to be an array of strings (i.e. "[["logo", "cd_branche", "lib_cranche"],[..],[..],[1111,22222,3333],[2222,324,432]").

In that case simply do:

Object[] obj = arg.toArray();
String[] headers =new String[obj.length];
for(int i=0;i<headers.length;i++) { 
    headers[i]= Arrays.toString(obj);
}

And each one of your ArrayList objects inside obj will be returned in string array format.

UPDATE: Since you want it as a flat array, you'll need to (a) compute the size of the array needed and (b) run through your object with two loops and make a deep search as such:

int size = 0;
for (int i = 0; i < arg.size(); size += arg.get(i++).size());

String[] headers =new String[size];
for(int count = 0, i=0;i<arg.size();i++) {
    for (int j=0; j< arg.get(i).size(); j++) {
        headers[count++]= arg.get(i).get(j).toString();
    }
}

edited Aug 13, 2015 at 14:43

answered Aug 13, 2015 at 14:33

Ori Lentz

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1 Comment

Manuel Faria Over a year ago

No, what I want is a String[] headers with headers[1]="logo" headers[2]="cd_branch" and so on

kraskixxx · Accepted Answer · 2015-08-13 14:31:08Z

0

String headers = "";
for (String header:arg) {headers += header;}

answered Aug 13, 2015 at 14:31

kraskixxx

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