How Do You Troubleshoot a Java Compilation Error “class fooBar is public, should be declared public class…”?

Problem scenario
You try to compile a java program, but you get this error:

hello.java:1: error: class HelloWorld is public, should be declared in a file named HelloWorld.java
public class HelloWorld {
^
1 error

What is wrong?

Solution
The .java file must have a name of "HelloWorld" like the public class in the error. If the .java file is called something else, it will not compile. The name must be case sensitively the same.

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