Oracle refuses to add optional parameters (and named args) to Java. So I did via a javac plugin and a smidge of hacking to modify the AST. The result is a pretty comprehensive implementation of the feature, without breaking binary compatibility. Here's a short summary.

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The manifold-params compiler plugin adds support for optional parameters and named arguments in Java methods, constructors, and records -- offering a simpler, more expressive alternative to method overloading and builder patterns.

    public String valueOf(char[] data, 
                          int offset = 0, 
                          int count = data.length - offset) {...}

    valueOf(array) // use defaults for offset and count
    valueOf(array, 2) // use default for count
    valueOf(array, count:20) // use default for offset by naming count

Key features:

- Optional parameters -- Define default values directly in methods, constructors, and records

- Named arguments -- Call methods using parameter names for clarity and flexibility

- Flexible defaults -- Use expressions, reference earlier parameters, and access local methods and fields

- Customizable behavior -- Override default values in subclasses or other contexts

- Safe API evolution -- Add parameters or change defaults without breaking binary or source compatibility

- Eliminates overloads and builders -- Collapse boilerplate into a single, expressive method or constructor

- IDE-friendly -- Fully supported in IntelliJ IDEA and Android Studio

Learn more: https://github.com/manifold-systems/manifold/blob/master/man...