Java SE 14 (March 2020) introduced a limited form of pattern matching as a preview feature, which becomes a permanent feature in Java SE 16 (March 2021).

Java’s character and assorted string classes offer low-level support for pattern matching, but that support typically leads to complex code. For simpler and more efficient coding, Java offers ...

The Observable design pattern is found in many Java APIs and in reactive programming. Here's an introduction to the timeless Observable pattern in Java.