Immutability in Java

1. Immutability in Java by Piotr Kafel (@PiotrKafel)
2. What does it mean that object is immutable ? Collections.unmodifiableCollection() ? Do we have some examples in JDK ?
3. Why should I care ?
4. How to ensure immutability ?
7. But what to do in such a case ?
8. "More computing sins are committed in the name of efficiency (without necessarily achieving it) than for any other single reason — including blind stupidity." W.A. Wulf
9. Thank you !