Add java17-features module: runnable demos and captured output for the ankurm.com java17-features article

java17-features/broken/RecordFieldMutation.java

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+/** Fails to compile on purpose: record fields are final. */
+public class RecordFieldMutation {
+    record Point(int x, int y) { void move() { this.x = 10; } }
+    public static void main(String[] args) { }
+}

java17-features/broken/SealedViolation.java

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+/** Fails to compile on purpose: a class that is not in the permits list cannot extend a sealed type. */
+public class SealedViolation {
+    sealed interface Shape permits Circle {}
+    record Circle(double r) implements Shape {}
+    record Triangle(double b, double h) implements Shape {}
+    public static void main(String[] args) { }
+}

java17-features/broken/SwitchPatternOn17.java

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+/** Fails on 17 without --enable-preview: pattern matching for switch is only a preview feature in 17 (JEP 406). */
+public class SwitchPatternOn17 {
+    static String f(Object o) { return switch (o) { case String s -> "string"; default -> "other"; }; }
+    public static void main(String[] args) { System.out.println(f("x")); }
+}