I've created a Java project based on a C# sample application that was
published under the Code Project Open License (CPOL)
There are two key parts to your question.
I've created a Java project
If you create a project, you usually own the copyright. You are permitted to license it however you please. (exception outside the scope of this question: work-for-hire, which is usually the case when you are paid to create intellectual property).
based on a C# sample application
...unless it is a derivative work. Then the path forward is less clear. In general if you create a clean room implementation you may be making software the interoperates with other software, or is conceptually based on other software. However, if you do not actually use any intellectual property, you generally own the copyright to the new work. Ask a lawyer who specializes in intellectual property law in your jurisdiction to be sure.
If your work is a derivative work, you must comply with the licensing terms of the original work, or negotiate different terms with the copyright owner of the original work.
- Determine if your work is an original or derivative work.
- If it is a derivative work, review the license with a lawyer or contact the original author for special licensing terms or to grant you full copyright control over your derivative work.