Please provide the meaning of below error

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Java

public class Test9 // getting error here
{
public static void run()
{
System.out.println("In run");
}

public static void fly()
{
System.out.println("In fly");
}
}

public class GoodDeveloper {

public static void main(String[] args) {
Test9.run();
Test9.fly();

}

}

What I have tried:

in the above commented line I am getting error like "the public type Test9 must be defined in its own file. Please suggest the meaning of this error( however i know the solution. i.e. removing public)

Please tell me why I cannot make my class as public