JDK 20: added example of Record pattern

wesleyegberto · wesleyegberto · commit 6533d39ddd22 · 2022-11-12T15:52:36.000-03:00
diff --git a/java-19/README.md b/java-19/README.md
@@ -15,7 +15,9 @@ To run each example use: `java --enable-preview --source 19 <FileName.java>`
 * Record patterns
   * added suport to deconstruct record values in pattern matcher
     * record pattern: `Point(int x, int y)`
-	* the variable `int x` is initialized with the result of accessor method `Point.x()`, not directly from the field `x`
+    * the variable `int x` is initialized with the result of accessor method `Point.x()`, not directly from the field `x`
+    * the variable doesn't need to be the same as the name of the record component
+    * the null value does not match any record pattern
   * now we can use type pattern and record pattern together
   * we can check the type and extract the record components using `instanceof` operator
     * `o instanceOf Point(int x, int y)`
diff --git a/java-20/README.md b/java-20/README.md
@@ -4,7 +4,18 @@ To run each example use: `java --enable-preview --source 20 <FileName.java>`
 
 ## Features
 
-Exploring... =)
+* Record patterns (second preview)
+  * added support for inference of type arguments of generic record patterns;
+    * now it generic type can be inferred
+    * given `record Decorator<T>(T t) {}` and variable `Decorator<Decorator<String>> wr`, thee record pattern generic type can be inferred in `w insteaceof Decorator(Decorator(var s))`
+  * added support for record patterns to appear in the headere of an enhanced for statement;
+    * `for (Point(var x, var y) : shapePoints)`
+  * remove support for named record pattner.
+
+## JEPs
+
+* [432](https://openjdk.java.net/jeps/432) - Record Patterns (Second Preview)
+* [433](https://openjdk.java.net/jeps/433) - Pattern Matching for switch (Fourth Preview)
 
 ## Links
 
diff --git a/java-20/RecordPatternsSecondPreviewTest.java b/java-20/RecordPatternsSecondPreviewTest.java
@@ -0,0 +1,50 @@
+/**
+ * To run: `java --enable-preview --source 20 RecordsPatternSecondPreviewTest.java`
+ */
+public class RecordPatternsSecondPreviewTest {
+	public static void main(String[] args) {
+		enhancedForLoop();
+	}
+
+	public static void enhancedForLoop() {
+		var points = new Point[] {
+			new Point(10, 10),
+			new Point(20, 20),
+			new Point(30, 30),
+			new Point(20, 50),
+			new Point(10, 60)
+		};
+
+		// we can now deconstruct a record type in the enhanced for loop
+		for (Point(int x, int y) : points) {
+			System.out.print("Drawing at x=%d and y=%d", x, y);
+		}
+	}
+
+	public static void genericInferrenceTest() {
+		var point = new Point(42, 42);
+		var decoratedPoint = new Decorator(new ColoredPoint(point, "RED"));
+		var anotherDecorated = new Decorator(decoratedPoint);
+
+		// here we don't need to use `Decorator<Decorator<ColoredPoint>>(Decorator<ColoredPoint>(ColoredPoint cp))` like in JDK 19
+		if (anotherDecorated instanceof Decorator(Decorator(ColoredPoint(Point(int x, int y), String color)))) {
+			System.out.println("Aren't you using too much decorator?");
+			System.out.printf("x=%d, y=%d; color=%s", x, y, color);
+		}
+	}
+
+	static void invalidGenericEnhancedForLoop() {
+		var items = new Decorator<Object>[] { new Object() };
+
+		// the pattern is not exhaustive (should be Decorator<Object>)
+		// for (Decorator<String> d : items) {
+		// }
+	}
+}
+
+record Point(int x, int y) {}
+
+record ColoredPoint(Point p, String color) {}
+
+record Decorator<T>(T t) {}
+
