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I am trying to create an ArrayList of Object[] from an Object[][] perform some changes and then getting a new Object[][] with the changes made.

However I get this compile error:

error: incompatible types: Object[] cannot be converted to Object[][]

when performing this:

protected Object[][] data;
fillData();
ArrayList dlist= new ArrayList<Object[]>( Arrays.asList(data) ); //NO COMPILE ERROR
Object[] example=new Object[2]; //just to use in toArray()

String [] args= {"new data 1","new data 2"};//yeah just a typo thanks Oscar
dlist.add( args ); //Sending String instead of Object is legal thanks Oscar.

data= dlist.toArray( example ); //COMPILER ERROR incompatible...

I am using the wrong statement with no compiler error: ArrayList dlist= new ArrayList<Object[]>( Arrays.asList(data) ); because the output is Object[] instead of Object[][] which is what i want Thanks for your help.

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3
  • List<Object[]> dlist= new ArrayList<Object[]>( Arrays.asList(data) ); compiles for me. What's your exact problem? Probably you didn't add the necessary imports or something. Commented Aug 11, 2014 at 0:54
  • dlist.add(<whatever>) works because you have declared ArrayList dlist which is raw, similar to declare ArrayList<Object> dlist which means you can store anything there. Commented Aug 11, 2014 at 0:55
  • What do you mean by I am using the wrong command, thanks for your help? Is your problem solved or what? Commented Aug 11, 2014 at 1:00

2 Answers 2

Reset to default
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I tried this piece of code and works:

Object[][] data = { { "hello", "world" }, { "bye", "world" } };
//convert Object[][] to List<Object[]>
List<Object[]> dlist = new ArrayList<>(Arrays.asList(data) );
for (Object[] o : dlist) {
    System.out.println(Arrays.deepToString(o));
}
//convert List<Object[]> to Object[][]
Object[][] data2 = dlist.toArray(new Object[0][]);
System.out.println(Arrays.deepToString(data2));

Also, Java language doesn't work with commands, except if you refer to the command line to compile your files, but that's outside the Java programming language.

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7 Comments

Object[][] data2 = dlist.toArray(new Object[dlist.size()][]); would avoid creating unnecessary garbage as well.
Object[][] data = dlist.toArray(new Object[dlist.size()][]); would be enough? i don't want to keep data "data". just the new. And Luiggi Object[][] data2 = dlist.toArray(new Object[0][]); should I put this in an iterator and replace 0 by a counter? or your statement is updating the whole two dimensional array?
@lrn2java I'm replacing the whole Object[][] 2d array.
@msandiford I leave that up to the JVM.
Okey thanks estimado, I will continue my little proyect and then do the reading on arrays and Lists, the deepToString seems to do the trick.
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Do it like this:

List<Object[]> dlist = new ArrayList<Object[]>();
for(Object[] i: data) {
    dlist.add(i);
}
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7 Comments

This is what OP is trying to avoid.
Can't see where in the question did he specify that he was trying to avoid this. Also, why?
Usage of Arrays#asList will suffice.
Can't see how ArrayList<Object[]> dlist = new ArrayList<Object[]>(Arrays.asList(objects)); doesn't compile though... it works on my machine.
That's the problem, it is an unclear question and we don't know the exact problem OP has.
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