Geeks, please accept the hero post of 2021 Microsoft x Intel hacking contest>>>

Multiple markers at this line
    - The value of the local variable people is not used
    - No enclosing instance of type TestExtends is accessible. Must qualify the allocation with an enclosing instance of type 
     TestExtends (e.g. x.new A() where x is an instance of TestExtends).

Solution: see if the class is written in another class

For example

public class TestExtends {
    public static void main(String[] args) {
        human people = new human();
    }
    
    class human{
        String name;
        
    }
}

The correct writing should be

public class TestExtends {
    public static void main(String[] args) {
        human people = new human();
    }
}

class human{
    String name;
    
}

This is a common mistake when learning object-oriented, hereby record QAQ