Java - definition - "principle of substitution"

Question

I read a summary which always use the definition "principle of substitution" when it talk about inheritance. But It doesn't explain the meaning of this principle.

What is this principle?

Thank you.

Answer 1

It means plainly: a subclass must honor the contract set by the super class.

If you extend a super class, you should read its document and implement as it dictates. That's all.

If I hear one more time "Liskov substitution" I'm going to kill a kitten.