Pattern Matching with Record Patterns

Simple Record Pattern Example

Imagine we define a record Monument:

Now, we want to print a message if the object is a Monument. Using record patterns, we can extract the name and year directly:

If you pass a Monument like the Eiffel Tower, it will print:

Notice that null will never match a record pattern — so no worries about null pointer exceptions here.

Using a Type Pattern Instead

You could also do it in a slightly different way by first capturing the Monument, then calling its methods:

Both approaches work! The record pattern version is just more compact when you need to immediately extract fields.

Working with Generic Records

Suppose you have a generic record like a box containing a monument:

You can pattern match a specific type inside the box:

⚠️ Important:
You must avoid unsafe casts. If you try to pattern match on a Box without a guaranteed type, it won’t compile.

Example of wrong code:

Type Inference with var

You don't always need to repeat the types. Java can infer them for you with var:

Shorter and cleaner!

Nested Record Patterns: Paris in Layers

You can even nest record patterns when working with more complex structures!

Imagine:

Now, let's print the latitude of the northern monument:

Example:

If north represents the Arc de Triomphe and south the Louvre Museum, the program will print the Arc’s latitude!

Nested Generic Example

You can nest patterns with generic types too. Example:

Here, even though you have a box inside a box, Java infers everything!

Summary

✨ With record patterns and type inference, Java makes it easier to work with structured data — whether you're describing points on a map or historic Paris monuments.

You can:

🟣 Check and extract values in one line

🟣 Avoid verbose code

🟣 Safely navigate nested structures