Java 27 and 26: runnable demos and captured output for every JEP, plus version lanes

Co-Authored-By: Claude Sonnet 5 <[email protected]> Claude-Session: https://claude.ai/code/session_01B38FGKKam5SCGgwgduVAh3
2026-09-21 14:47:46 +00:00
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+import jdk.incubator.vector.FloatVector;
+import jdk.incubator.vector.VectorOperators;
+import jdk.incubator.vector.VectorSpecies;
+
+/**
+ * JEP 537, Vector API (twelfth incubator). The same source and the same class file run on JDK 26
+ * (eleventh incubator, JEP 529) and JDK 27, because the public API did not change between them:
+ * docs/output/50-vector-api-surface.txt is the javap diff that shows it. For what the API is and
+ * how to use it well, see the companion guide to JEP 537 on ankurm.com.
+ * Run with --add-modules jdk.incubator.vector.
+ */
+public class VectorDemo {
+    static final VectorSpecies<Float> SPECIES = FloatVector.SPECIES_PREFERRED;
+
+    static float scalarDot(float[] a, float[] b) {
+        float sum = 0;
+        for (int i = 0; i < a.length; i++) {
+            sum += a[i] * b[i];
+        }
+        return sum;
+    }
+
+    static float vectorDot(float[] a, float[] b) {
+        int i = 0;
+        FloatVector acc = FloatVector.zero(SPECIES);
+        int bound = SPECIES.loopBound(a.length);
+        for (; i < bound; i += SPECIES.length()) {
+            acc = FloatVector.fromArray(SPECIES, a, i).fma(FloatVector.fromArray(SPECIES, b, i), acc);
+        }
+        float sum = acc.reduceLanes(VectorOperators.ADD);
+        for (; i < a.length; i++) {          // the tail the vector loop could not cover
+            sum += a[i] * b[i];
+        }
+        return sum;
+    }
+
+    public static void main(String[] args) {
+        System.out.println("java.version      = " + System.getProperty("java.version"));
+        System.out.println("preferred species = " + SPECIES + "  (" + SPECIES.length() + " float lanes, machine dependent)");
+        int n = 1_000_003;                       // deliberately not a multiple of the lane count
+        float[] a = new float[n], b = new float[n];
+        for (int i = 0; i < n; i++) {
+            a[i] = (i % 7) * 0.5f;
+            b[i] = (i % 5) * 0.25f;
+        }
+        float scalar = scalarDot(a, b);
+        float vector = vectorDot(a, b);
+        System.out.println("scalar dot        = " + scalar);
+        System.out.println("vector dot        = " + vector);
+        // Floating-point addition is not associative, so the two sums differ in the last bits; compare with a tolerance.
+        Check.that(Math.abs(scalar - vector) / Math.abs(scalar) < 1e-3, "vector and scalar dot products agree to within 0.1%");
+    }
+}