无法从数组列表中删除哈希映射

Question

public class PurchaseOrderWrapper extends ArrayList<HashMap<String, String>> {

        public boolean contains(Object o) {
            HashMap<String, String> ob = (HashMap<String, String>) o;
            for (HashMap<String, String> map : this) {
                Log.i("kasun",ob.get("part_no")+" "+ map.get("part_no")+" = "+Boolean.toString(ob.get("part_no").equalsIgnoreCase(map.get("part_no"))));
                 if(ob.get("part_no").equalsIgnoreCase(map.get("part_no"))){
                     return true;
                 }
            }
        return false;
    }
}

if (wrapper.contains(removitems)){      
    wrapper.remove(removitems);     
} 

Wrapper is a instance of a PurchaseOrderWrapper class.it contains Hash Map with with 5 attributes including part no.remove items also contains 4 items inclding part no as i mention on the above example.So i need to remove the hashmap from Wrapper instance which has same part no in remove items hash map.But it does not work

Answer 1

You're extending ArrayList (which you should never do), and breaking its contract.

You override contains() by saying that your list contains a given object if this object is a HashMap and happens to contain the same value for the "part_no" key as another map in the list. But you don't override remove(). And remove() keeps using the ArrayList's method, which removes the element in the list that is equal to the object passed as argument.

Don't, ever, extend the collection classes. Instead, wrap them inside your own class.

To implement the remove method, you'll probably have to iterate over the list, find the map in the list which has the same value for the "part_no" key as the map passed as argument, and remove that map from the list.

I have the suspicion that you're using Maps where you should define your own class ad well, but that doesn't change much.

Here's the skeleton of the class that you should have. You should figure out the implementation by yourself based on the above indications:

public class PurchaseOrderWrapper {
    private List<Map<String, String>> list = new ArrayList<>();

    public boolean containsElementWithSamePartNoAs(Map<String, String> map) {
        // iterate over the list and find if an element has the same part_no
        // as the map passed as argument
    }

    public void removeElementWithSamePartNoAs(Map<String, String> map) {
        // iterate over the list and find the element which has the same part_no
        // as the map passed as argument. Once found, remove this element from the list
    }
}