Treemap Entry converted to String types fails

Question

I have two collections where both the keys and the values are strings. I need the collections to be ordered, so I decided to use "TreeMap" to keep the ordering.

I want to:

1) print out the two collections, 'garList' and 'noGarList', respectively;

2) compare each and every element of the first collection with each and every element of the second collection;

3) remove from the first collection ('garList') those elements that appear in the second collection ('noGarList') as well.

I wrote the following code to do these 3 tasks:

public class TryTask_A_copy {

public static void main(String[] args) {

    // First collection:
    TreeMap<String, String> garList = new TreeMap<>();
    // Second collection:
    TreeMap<String, String> noGarList = new TreeMap<>();

    // Fill the "Properties" obj for 'Gar':
    garList.put("Gar_1", "rotura de lunas");
    garList.put("Gar_2", "arbitraje de ley");
    garList.put("Gar_3", "Adaptación del hogar");

    // Fill the "Properties" obj for 'noGar':
    noGarList.put("noGar_1", "rotura de lunas");
    noGarList.put("noGar_2", "reembolso total");
    noGarList.put("noGar_3", "Adaptación del coche");    

    // Get a set of the entries:
    Set garSet = garList.entrySet();
    Set noGarSet = noGarList.entrySet();

    // Def strings needed for the comparison:
    String strGar;
    String strNoGar;

    // Get an iterator:
    Iterator i_gar = garSet.iterator();
    Iterator i_noGar = noGarSet.iterator();

    // Display 'Gar' elements:
    while(i_gar.hasNext()){
        String me_Gar = (String)i_gar.next();  // Exception in thread "main" java.lang.ClassCastException: java.util.TreeMap$Entry cannot be cast to java.lang.String
        strGar = (String) i_gar.next();  
        System.out.println(strGar + " : " + garList.get(strGar) + "."); 
    }
    System.out.println();

    // Display 'noGar' elements:
    while(i_noGar.hasNext()){
        String me_noGar = (String)i_noGar.next();
        strNoGar = (String) i_noGar.next();  
        System.out.println(strNoGar + " : " + garList.get(strNoGar) + "."); 
    }

    // Get new iterators:
    Iterator itr_gar = garSet.iterator();
    Iterator itr_noGar = noGarSet.iterator();

    // Compare elements from 'Gar' list with elements from 'noGar' list
    // and remove those elements from 'Gar' list that appear in 'noGar' list as well:
    while(itr_gar.hasNext()){
        strGar = (String) itr_gar.next();  
        while(itr_noGar.hasNext()){
            String str1 = garList.get(strGar);
            strNoGar = (String) itr_noGar.next();  
            String str2 = noGarList.get(strNoGar);
            boolean result = str1.equalsIgnoreCase(str2);
            System.out.println(strGar + " : " + str1 + ".");
            System.out.println(strNoGar + " : " + str2 + ".");
            System.out.println(result);
            System.out.println();
            // if an element appears in both lists, then remove this element from "Gar" list:
            if(result != true){
            } else {
                Object garList_new = garList.remove(strGar);
                System.out.println("Removed element: " + garList_new);  
                System.out.println();
            }
        }
        itr_noGar = noGarSet.iterator();
    }
  }

}

But I get:

Exception in thread "main" java.lang.ClassCastException: java.util.TreeMap$Entry cannot be cast to java.lang.String" at line 51 (see comments).

I understand that the elements of my two TreeMap objects are of "Map Entry" type and cannot be converted to "String" type, is that correct?

But then how can I get an ordered collection where both the keys and the values are Strings?

Writing something like garSet.removeAll(noGarSet) does not work because this would imply that both key AND value coincide. But in my case I have some of the values in the two collections coinciding while having different keys.

So I need a solution to the following: have an ordered collection where both keys and values are Strings and where values can be compared and removed.

Can you please help me out with this?

Answer 1

I'm a little unclear on just what you are trying to achieve but if you want to remove based on keys then just do:

garSet.removeAll(noGarSet);

Your code in general seems to be far more complex than it needs to be for what you are trying to achieve. For example to print all the Strings in the Map just do:

for (Entry<String, String> entry: garMap.entrySet()) {
    System.out.println(entry.key() + " : " + entry.value() + "."); 
}

If you do:

map1.keySet().removeAll(map2.keySet()) 

then that will remove all the duplicates based on key.

map1.values().removeAll(map2.values()) 

will remove all duplicates based on value.

map1.entryset().removeAll(map2.entrySet())

will remove all duplicates based on key/value pairs.