copy on write semantics

[boojongmin]

• wiki
• reids COW

source

CopyOnWriteArrayList

public boolean add(E e) {
        synchronized (lock) {
            Object[] es = getArray();
            int len = es.length;
            es = Arrays.copyOf(es, len + 1);
            es[len] = e;
            setArray(es);
            return true;
        }
    }

CopyOnWriteArrayList

    private transient volatile Object[] array;

public Iterator<E> iterator() {
        return new COWIterator<E>(getArray(), 0);
    }

final Object[] getArray() {
        return array;
    }