Dependency Injection? Mocking Objects?

I am new to Dependency Injection and Mocking Objects and nearly know nothing about them though I can guess from their names somehow! I� really appreciate if you could share with me your knowledge & experience� to understand these 2 architectural concepts.

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What is Dependency Injection? How to implement it? When to implement it? Why to implement it (what problem it tries to solve)? Any code sample or screencasts?

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What are mocking objects? How to implement them? When to implement them? why to implement them (what problem they try to solve)? Any code sample or screencasts?

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Many thanks
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