How to autocomplete lambdas in IntelliJ IDEA?

In Windows or Linux, it’s Ctrl+Space

In Mac OS, it’s Ctrl+Shift+Space

You can just type p = s -> f..., autocompletion will then suggest false. If you're not sure about lambda, you can start with the inner class, and then turn it into a lambda expression.

In your example you can press Alt+Enter afterwards, as follows:

After completing:

After pressing Alt+Enter:

Result:

Clicking the small icon at the gutter shows you the Predicate.test method.