Difference between HashMap and ConcurrentHashMap in Java

Following are the notable differences between HashMap and ConcurrentHashMap classes in Java.

Example

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;
public class Tester {
   public static void main(String[] args) {
      List<String> arrayList = new ArrayList<>();
      arrayList.add("A");
      arrayList.add("B");
      arrayList.add("C");
      Iterator<String> iterator = arrayList.iterator();
      System.out.println(arrayList);
      while (iterator.hasNext()) {
         if (iterator.next().equals("C")) {
            //removal is allowed.
            iterator.remove();
         }
      }
      System.out.println(arrayList);
      List<String> copyOnWriteArrayList = new CopyOnWriteArrayList<>();
      copyOnWriteArrayList.add("A");
      copyOnWriteArrayList.add("B");
      copyOnWriteArrayList.add("C");
      Iterator<String> iterator1 = copyOnWriteArrayList.iterator();
      System.out.println(copyOnWriteArrayList);
      while (iterator1.hasNext()) {
         if (iterator1.next().equals("C")) {
            try{
               iterator1.remove();
            }catch(UnsupportedOperationException e){
               System.out.println("Removal not allowed.");
            }
         }
      }
      System.out.println(copyOnWriteArrayList);
   }
}

Output

[A, B, C]
[A, B]
[A, B, C]
Removal not allowed.
[A, B, C]