Cut Java 21 Record Pattern Matching Code in Half

Java 21 introduces switch pattern matching and record deconstruction, allowing developers to replace lengthy instanceof checks with concise code.

record Point(int x, int y) {}

static void printSum(Object obj) {
    if (obj instanceof Point p) {
        int x = p.x();
        int y = p.y();
        System.out.println(x + y);
    }
}

Before Java 21, extracting the fields of a Point required four lines of code; with pattern matching it can be done in just two lines:

static void printSum(Object obj) {
    if (obj instanceof Point(int x, int y)) {
        System.out.println(x + y);
    }
}

In real projects records are often nested. Consider the following records:

record Size(int width, int height) {}
record Point(int x, int y) {}
record WindowFrame(Point origin, Size size) {}

To print the height of the Size inside a WindowFrame the traditional approach would be:

if (obj instanceof WindowFrame wf) {
    if (wf.size() != null) {
        System.out.println("Height: " + wf.size().height());
    }
}

Java 21 allows nested deconstruction, reducing the above to a single check:

if (obj instanceof WindowFrame(Point origin, Size(int width, int height))) {
    System.out.println("Height: " + height);
}

The image below illustrates the record hierarchy used in the examples.