The public type Test1 must be defined in its own file

This error message usually occurs when you have defined a public class or interface in a Java file whose name does not match the class/interface name. To fix this error, you can do one of the following:

1. Rename the Java file to match the public class/interface name.
2. Move the public class/interface to a new Java file with the correct name.
3. Make the class/interface package-private (remove the "public" modifier) if it does not need to be accessed from outside its package.

Here's an example:

// file name: MyClass.java
public class Test1 {
// ...
}

In this case, the file name should be renamed to Test1.java to match the public class name.