Question

I’m getting an error on this line

tm.put(temp[j],tm.get(temp[j]).add(i));

when i was compiling my program in eclipse:

The method put(String, ArrayList<Integer>) in the type TreeMap<String,ArrayList<Integer>> is not applicable for the arguments (String, boolean)

The followings are my codes:

TreeMap<String, ArrayList<Integer>> tm=new TreeMap<String, ArrayList<Integer>>();
String[] temp=folders.split(" |,");
for (int j=1;j<temp.length;j++){

            if (!tm.containsKey(temp[j])){
                tm.put(temp[j], new ArrayList<Integer>(j));
            } else {
                tm.put(temp[j],tm.get(temp[j]).add(j));
            }
        }

the folders is something like this

folders="0 Jim,Cook,Edward";

I’m wondering why there’s no error on the former put method, but only on the second one.

Answer 1

ArrayList.add(E) returns a boolean, you simply cannot chain them up.

tm.get(temp[j]).add(j); is enough, you don’t need to put again.

new ArrayList<Integer>(j) won’t give you an arraylist of one element, the argument is the initialCapacity.

Then, you should declare tm as Map<String, List<Integer>>.

Map<String, List<Integer>> tm=new TreeMap<String, List<Integer>>();
String[] temp=folders.split(" |,");
for (int j=1;j<temp.length;j++){

    if (!tm.containsKey(temp[j])){
        tm.put(temp[j], new ArrayList<Integer>());
    }
    tm.get(temp[j]).add(j); // This will change the arraylist in the map.

}