Pattern Matching for instanceof & Record Patterns (Java 21+)

1Concept

Java 16 introduced pattern matching for `instanceof`, eliminating redundant casts (`if (obj instanceof String s)`). Java 21 added Record Patterns (JEP 440), enabling direct deconstruction of record components directly in `if` and `switch` expressions.

2Architecture Diagram

Old Java:  if (obj instanceof Point) { Point p = (Point) obj; int x = p.x(); }
Java 21:   if (obj instanceof Point(int x, int y)) { ... direct access to x, y! }

3Code Example

public class RecordPatternsDemo {
    record Point(int x, int y) {}
    record Box(Point topLeft, Point bottomRight) {}

    public static void printPoint(Object obj) {
        // Record deconstruction pattern
        if (obj instanceof Point(int x, int y)) {
            System.out.println("Deconstructed Point -> X: " + x + ", Y: " + y);
        }
    }

    public static void main(String[] args) {
        Point p = new Point(10, 25);
        printPoint(p);
    }
}

4Expected Output

Deconstructed Point -> X: 10, Y: 25

5Key Takeaways

• ✓Record patterns deconstruct nested records cleanly without manual accessor calls.
• ✓Eliminates ClassCastException and eliminates boilerplate getter calls.
• ✓Combines with switch expressions for high-level functional data extraction.