meowpunch

public class Square {
    public Point topLeft;
    public double side;
}

public class Rectangle {
    public Point topLeft;
    public double height;
    public double width;
}

meowpunch

public class Square implements Shape {
    private Point topLeft;
    private double side;

    public double area() {
        return side * side;
    }
}

public class Rectangle implements Shape {

meowpunch

sealed interface Shape {}

record Point(double x, double y) {}

record Square (Point topLeft, double side) implements Shape {}

record Rectangle (Point topLeft, double height, double width) implements Shape {}

record Circle (Point center, double radius) implements Shape {}

meowpunch

sealed trait Shape

case class Point(x: Double, y: Double) {}

case class Square(topLeft: Point, side: Double) extends Shape {}

case class Rectangle(topLeft: Point, height: Double, width: Double) extends Shape {}

case class Circle(center: Point, radius: Double) extends Shape {}

meowpunch

// x is automatically cast to String
if (obj is String) { return obj.length }
x is String && x.length == 0 

// compile error
x is String || x.length == 0 

// with `when` expression
when (x) {
    is String -> x.length

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// without type patterns
if (obj instanceof String) { return ((String) s).length(); }

// type patterns, cast to String and assign to s
if (obj instanceof String s) { return s.length(); }

x instanceof String s && s.length()

// compile error, out of scope
x instanceof String s || s.length()

meowpunch

enum DayOfWeek { SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY }

public class SwitchEnum {
    // switch statement
    public boolean isWeekendStatement(DayOfWeek day) throws NoSuchDayOfWeekException {
        boolean isWeekend;
        
        switch (day) {
            case MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY:
                isWeekend = false;

meowpunch

record Point(int x, int y) {}
enum Color { RED, GREEN, BLUE }
record ColoredPoint(Point p, Color c) {}
record Rectangle(ColoredPoint upperLeft, ColoredPoint lowerRight) {}

static void printXCoordOfUpperLeftPointBeforePatterns(Rectangle r) {
    if (r == null) return;
    ColoredPoint ul = r.upperLeft();
    if (ul == null) return;
    Point p = ul.p();