Problems with threads --- Simple Observer Pattern

We usually use observer pattern like following

[i]public synchronized  void addListener(listener) {…}

public synchronized  void setValue(newValue) {
    myValue = newValue;

    for (int i = 0; i < myListeners.length; i++) {
        myListeners[i].valueChanged(newValue)
    }
}[/i]

[b]What’s wrong with this (in a multithreaded context)?
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