What does the Java assert keyword do, and when should it be used?

Question

What are some real life examples to understand the key role of assertions?

Answer 1

In addition to all the great answers provided here, the official Java SE 7 programming guide has a pretty concise manual on using assert; with several spot-on examples of when it's a good (and, importantly, bad) idea to use assertions, and how it's different from throwing exceptions.

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