Question

I am trying to designing a software that convert a flowchart into java or any other code. However I repeatedly getting the ConcurrentModificationException..
But I can’t use a boolean to prevent concurrentModification, because access to the linked list happens in various places.

So as a solution I created the below adapter class. However it also throws the same exception from next method. Are there any other solution or if can, plz let me know how to modify my codes…

thank you very much…

import java.util.Iterator;
import java.util.LinkedList;

public class LinkedListAdapter<T> extends LinkedList<T>{

@Override
public boolean add(T t){

    boolean b;

    synchronized(this){
        b = super.add(t);
    }

    return b;
}

@Override
public T remove(){

    T t;

    synchronized(this){
        t = super.remove();
    }

    return t;
}

@Override
public Iterator<T> iterator(){

    final LinkedListAdapter<T> adap = this;

    return 
        new Iterator<T>(){

        private Iterator<T> iter;

        {
            synchronized(adap){
                iter = LinkedListAdapter.this.getIterator();
            }
        }

        @Override
        public boolean hasNext() {

            boolean b;

            synchronized(adap){
                b = iter.hasNext();
            }

            return b;
        }

        @Override
        public T next() {

            T t;

            synchronized(adap){
                t = iter.next();
            }

            return t;
        }

        @Override
        public void remove() {
            throw new UnsupportedOperationException();
        }
    };
}

protected Iterator<T> getIterator() {

    Iterator<T> iter;

    synchronized(this){
        iter = super.iterator();
    }

    return iter;
}
}

Answer 1

The ConcurrentModificationException is usually thrown when iterating through the list and in the same time usually another thread or even the same loop tries to modify (add / remove) the contents of the list.