Handling Concurrent Modification Exceptions in Java Collections

Today we have faced below problem when trying to remove a object from a list

Exception in thread "main" java.util.ConcurrentModificationException
 at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:449)
 at java.util.AbstractList$Itr.next(AbstractList.java:420)
 at ConcurrentModificationException.removeObjectTwo(ConcurrentModificationException.java:28)
 at ConcurrentModificationException.main(ConcurrentModificationException.java:20)

Below is the code

public class ConcurrentModificationException
{

  public static void main(String[] args)
  {

    A a=new A("sneha","prasanth");
    A a1=new A("pradeep","hima");
    A a2=new A("praveen","subz");
    
    List<A> list=new ArrayList<A>();
    list.add(a);list.add(a1);list.add(a2);
    
    B b=new B();
    b.setAList(list);
    
    removeObjectTwo(b,a1);
    
    System.out.println(b.getAList());
    
  }
  
  private static void removeObjectTwo(B b,A aToBeRemoved){
    
  for(A a : b.getAList()){
  b.removeA(a);
  }
 }
}

class B {
  
  private List<A> aList=new ArrayList<A>();

  public List<A> getAList()
  {
    return aList;
  }

  public void setAList(List<A> list)
  {
    aList = list;
  }
  
  public void removeA(A a) {
    aList.remove(a);
    a.delete();
  }
}

class A {
  
  private String firstName;
  private String lastName;
  private String isDeleted="N";
  
  A(String firstName,String lastName) {
    this.firstName=firstName;
    this.lastName=lastName;
  }
  
  public String getIsDeleted()
  {
    return isDeleted;
  }
  public void setIsDeleted(String isDeleted)
  {
    this.isDeleted = isDeleted;
  }
  public String getFirstName()
  {
    return firstName;
  }
  public void setFirstName(String firstName)
  {
    this.firstName = firstName;
  }
  public String getLastName()
  {
    return lastName;
  }
  public void setLastName(String lastName)
  {
    this.lastName = lastName;
  }
  
  public void delete() {
    this.isDeleted="Y";
  }
  
  public String toString() {
    return firstName + ":" + lastName;
  }
   
}

Once you have changed the below method it works perfectly

 private static void removeObjectTwo(B b,A aToBeRemoved){
    
    List<A> dupA=new ArrayList<A>();
    
    for(A a : b.getAList()){
      if(aToBeRemoved.equals(a))
        dupA.add(a);
    }
    
    for (A a : dupA)
    {
      b.removeA(a);
    }

  }
}

Lesson: Never try to do both read/write on the same collection object and better try to take 2 seperate lists and do the way it was done as shown in the above code.