I am trying to understand the SynchronizedMap and I ran the below code. I get the below Output with an exception. According to my understanding the exception is caused when the get() methods are trying to access the syncmap when a thread is still executing a write on the map or Thread is in the Sleep state. Is my understanding correct or am I missing something ?

class MapHelper1 implements Runnable {
Map<String, Integer> map;

public MapHelper1(Map<String, Integer> map) {
    this.map = map;
    new Thread(this, "MapHelper1").start();
}

public void run() {
    map.put("One", 1);
    try {
        System.out.println("MapHelper1 sleeping");
        Thread.sleep(100);
    } catch (Exception e) {
        System.out.println(e);
    }

}
}

class MapHelper2 implements Runnable { 
Map<String, Integer> map;

public MapHelper2(Map<String, Integer> map) {
    this.map = map;
    new Thread(this, "MapHelper3").start();
}

public void run() {
    map.put("two", 1);
    try {
        System.out.println("MapHelper2 sleeping");
        Thread.sleep(100);
    } catch (Exception e) {
        System.out.println(e);
    }

}
}

class MapHelper3 implements Runnable {
Map<String, Integer> map;

public MapHelper3(Map<String, Integer> map) {
    this.map = map;
    new Thread(this, "MapHelper3").start();
}

public void run() {
    map.put("three", 1);
    try {
        System.out.println("MapHelper3 sleeping");
        Thread.sleep(100);
    } catch (Exception e) {
        System.out.println(e);
    }

}
}

public class MainClass {

public static void main(String[] args) {
    Map<String, Integer> hashMap = new HashMap<>();
    Map<String, Integer> syncMap = Collections.synchronizedMap(hashMap);
    MapHelper1 mapHelper1 = new MapHelper1(syncMap);
    MapHelper2 mapHelper2 = new MapHelper2(syncMap);
    MapHelper3 mapHelper3 = new MapHelper3(syncMap);

    for (Map.Entry<String, Integer> e : syncMap.entrySet()) {
        System.out.println(e.getKey() + "=" + e.getValue());
    }

}

}

OUTPUT:

MapHelper1 sleeping
MapHelper2 sleeping
MapHelper3 sleeping

Exception in thread "main" java.util.ConcurrentModificationException
at java.base/java.util.HashMap$HashIterator.nextNode(HashMap.java:1494)
at java.base/java.util.HashMap$EntryIterator.next(HashMap.java:1527)
at java.base/java.util.HashMap$EntryIterator.next(HashMap.java:1525)
at MainClass.main(MainClass.java:137)
Command exited with non-zero status 1

I know this is marked "solved", bt for the benefit af anyone who has the same problem...

To quote from the API doc...

It is imperative that the user manually synchronize on the returned map when iterating over any of its collection views

so the loop on lines 70-72 must be explicitly synchronised