How should java classes be organized?

I am new to Java and to Android development. In all the tutorials at my current level of understanding, the only user-created classes are found in the directory app/src/main/java/com.example.project/, and all these classes refer to views.

In my project, I will need to write a number of classes which are not directly related to any particular views. For example, a TextToSpeech class and a PatternRecognition class.

What are considered to be the best practices for managing the class files in the directory hierarchy? What online resources can you recommend, so that I can explore this question in more detail?

Solution

I'm not sure, that this is the best way, but my Android projects looks like this:

src
├───androidTest
│   └───java
│       └───hu
│           └───company
│               └───app
│                   └───activities
│                       ├───login
│                       └───main
└───main
    ├───assets
    │   └...
    ├───java
    │   └───hu
    │       └───company
    │           └───app
    │               ├───activities
    │               │   ├───login
    │               │   ├───main
    │               │   ├───mainMenu
    │               │   └───surveys
    │               ├───common
    │               └───communication
    └───res
        └──...

And in the hu.company.app package, I have more packages. All of my Activities in the activities package, sorted by their functionality. And I have other classes in upper packages.

When I started this project, I could'nt find any docs about the "best" Android project structure. I'm not sure, that this is a right project structure, but it works.