public synchronized X getAnotherX(){
if(iterator.hasNext()){
X b = iterator.next();
String name = b.getInputFileName();
...
return b;
}
else{return null;}
}
despite the synchronized statement in the declaration header, i still get a ConcurrentModificationException Exception at the line where i use iterator.next(); whats wrong here ?
Below example is just the demo for this:
public class SynchronizedListDemo {
public static void main(String[] args) throws InterruptedException {
List<Integer> list = new ArrayList<>();
for(int i=0;i<100000;i++){
System.out.println(i);
list.add(i);
}
// Synchronzied list will also give ConcurrentModificationException, b'coz
// it makes only methods thread safe, but you are still modifying list while iterating it.
// You can use 'ListIterator' or 'CopyOnWriteArrayList'
List<Integer> list1 = Collections.synchronizedList(list);
Runnable r1= ()->{
for(Integer i: list1)
System.out.println(i);
};
Runnable r2 = ()->{
try {
System.out.println();
System.out.println("Removing....");
//list1.add(4); // Will give ConcurrentModificationException
System.out.println("Removed");
} catch (Exception e) {
e.printStackTrace();
}
};
// This will not give ConcurrentModificationException as it work on the copy of list.
List<Integer> list2 = new CopyOnWriteArrayList<>(list);
Runnable r3= ()->{
for(Integer i: list2)
System.out.println(i);
};
Runnable r4 = ()->{
try {
System.out.println();
System.out.println("Removing....");
list2.add(4);
System.out.println("Removed");
} catch (Exception e) {
e.printStackTrace();
}
};
Thread t1 = new Thread(r3);
Thread.sleep(100);
Thread t2 = new Thread(r4);
t1.start();
t2.start();
System.out.println("Done");
}
}