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What are good reasons to prohibit inheritance in Java, for example by using final classes or classes using a single, private parameterless constructor? What are good reasons of making a method final?
Your best reference here is Item 19 of Joshua Bloch’s excellent book "Effective Java", called "Design and document for inheritance or else prohibit it". (It’s item 17 in the second edition and item 15 in the first edition.) You should really read it, but I’ll summarize.
The interaction of inherited classes with their parents can be surprising and unpredictable if the ancestor wasn’t designed to be inherited from.
Classes should therefore come in two kinds:
Classes designed to be **extended**, and with enough documentation to describe how it should be done
Classes marked **final**
If you are writing purely internal code, this may be a bit of overkill. However, the extra effort involved in adding five characters to a class file is very small. If you are writing only for internal consumption, then a future coder can always remove the ‘final’ – you can think of it as a warning saying "this class was not designed with inheritance in mind".