illegalStateException when using iterator.remove ()

Question

I have a problem with iterator remove which is causing IllegalStateException. The error is occurring in

depIterator.remove() I'm not sure why this is occurring. Any help would be appreciated.

List<Dependency> listofAllDependency = new ArrayList<Dependency>();

    while(!dependencyTable.isEmpty()){          
        //allValuesDependentsAreBuilt = false;
        Iterator<Entry<Dependency, List<Dependency>>> depIterator = dependencyTable.entrySet().iterator();

        while(depIterator.hasNext()){
            ArrayList<String> allValuesDependentsAreBuilt = new ArrayList<String>();

            Entry<Dependency, List<Dependency>> depEntry = depIterator.next();


            //If the key's values have no dependencies
            if(depEntry.getValue().size()==0){
                //System.out.println(depEntry.getKey());
                listofAllDependency.add(depEntry.getKey());
                dependencyTable.remove(depEntry); 
                depIterator.remove(); 
            }

            for(Dependency dep :depEntry.getValue()){

                if(!dependencyTable.containsKey(dep)){
                    allValuesDependentsAreBuilt.add("true"); 
                }else
                {
                    allValuesDependentsAreBuilt.add("false"); 
                }
            }

            if(!allValuesDependentsAreBuilt.contains("false")){ 

                listofAllDependency.add(depEntry.getKey());
                dependencyTable.remove(depEntry);
                depIterator.remove();
            }

        }
    }

Answer 1

It seems following line is culprit:

dependencyTable.remove(depEntry); 

Don't do add/remove on datastructure while iterating (which will cause IllegalStateException ) .

Following should be enough:

  depIterator.remove(); 

Answer 2

When looping over a data structure and adding or removing contents of that datastructure at the same time, you can run into problems. If you want to remove items from a list while iterating over the list I would recommend keeping track of what you want to remove and then removing it all after you are done looping. Looking at your code specifically I would keep this line

dependencyTable.remove(depEntry);

and take out the line of code that modifies the iterator