Java 25: Flexible constructor bodies (JEP 513)

JavaReleases/src/test/java/pl/mperor/lab/java/Java25.java

@@ -38,4 +38,64 @@ public void testPrintFromIOClass() {
         TestUtils.resetSystemOut();
     }
 
-}
+    @Test
+    public void testValidateArgumentBeforeSuperCall() {
+        Assertions.assertEquals(5, new PositiveBox(5).value);
+        Assertions.assertThrows(IllegalArgumentException.class, () -> new PositiveBox(-1));
+    }
+
+    static class Box {
+        final int value;
+
+        Box(int value) {
+            this.value = value;
+        }
+    }
+
+    /// Before JEP 513, validating/transforming `value` required a private static
+    /// helper method invoked inside `super(...)`, since no statement could precede it.
+    static class PositiveBox extends Box {
+        PositiveBox(int value) {
+            if (value <= 0) {
+                throw new IllegalArgumentException("value must be positive: " + value);
+            }
+            super(value);
+        }
+    }
+
+    @Test
+    public void testFieldAssignedBeforeSuperVisibleToOverriddenMethod() {
+        var circle = new Circle(2.5);
+        Assertions.assertEquals("circle r=2.5", circle.description);
+    }
+
+    static class Shape {
+        Shape() {
+            describe(); // an overridable method invoked from the superclass constructor
+        }
+
+        void describe() {
+        }
+    }
+
+    static class Circle extends Shape {
+        final double radius;
+        String description;
+
+        Circle(double radius) {
+            // Still forbidden in the prologue (would not compile here, before super()):
+            //   System.out.println(this);    // cannot reference `this`
+            //   describe();                  // cannot call an instance method
+            //   System.out.println(radius);  // cannot read an own field back
+            this.radius = radius; // JEP 513: assigning an own field is now allowed before super()
+            super();
+        }
+
+        @Override
+        void describe() {
+            // radius is already set here, even though super() has not returned yet
+            description = "circle r=" + radius;
+        }
+    }
+
+}