Solve issue java.lang.ClassNotFoundException while building project in Eclipse -- part 1 -- Eclipse

In this video, I will teach you how to:
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Major reason:

Why it does NOT build successfully at compile time?
There are lots of reasons:
1. Either missing or wrong settings about Kotlin Compiler. It possibly may cause the jdk NOT found at compile time.
2. Either missing or wrong settings about Java -- Build Path.

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Example of Compiler Error:

Error: Could not find or load main class Kotlin_v9Kt

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My notes:

Available in Github.