I know how to add an object:
ArrayList<Object> ob = new ArrayList<Object>();
ob.add (index, some_object);
But let say the object has a field called 'name', how can I change that single field only?
For example:
ob.setName(name);
(I know this does not work.)
There's no special treatment here:
ArrayList<SomeObjectType> ob = new ArrayList<SomeObjectType>();
//...
ob.add(index, some_object);
some_object.setName(name);
The object you wanted to set name for is some_object, not ob.
If you are asking about a situation where you have a List which contains the object you want to update, but you don't yet have a reference to that object, then you will need to first find the object within the list, and then update its name field.
If you do have the reference to the object, then the fact that it is contained in a list is irrelevant: call some_object.setName(name) and the object will have the new name whether it is fetched from the list or directly.
I think maybe you want to see
public void stuff(List<? extends Foo> list, int indexToAlter){
// Get the item in the list at the index and call the appropriate method
list.get(indexToAlter).methodOnFoo();
}
You seem to be confusing the list you are storing your object in and the object itself. Try something like:
Object temp = ob.get(index);
temp.name = new_name;
ob. Common practice would be something likeobjects(i.e. plural form) or something like that...