8346609: Improve MemorySegment.toString

Reviewed-by: mcimadamore

Author: minborg

src/java.base/share/classes/jdk/internal/foreign/AbstractMemorySegmentImpl.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -486,9 +486,18 @@ public int characteristics() {
 
     @Override
     public String toString() {
-        return "MemorySegment{ " +
-                heapBase().map(hb -> "heapBase: " + hb + ", ").orElse("") +
-                "address: " + Utils.toHexString(address()) +
+        final String kind;
+        if (this instanceof HeapMemorySegmentImpl) {
+            kind = "heap";
+        } else if (this instanceof MappedMemorySegmentImpl) {
+            kind = "mapped";
+        } else {
+            kind = "native";
+        }
+        return "MemorySegment{ kind: " +
+                kind +
+                heapBase().map(hb -> ", heapBase: " + hb).orElse("") +
+                ", address: " + Utils.toHexString(address()) +
                 ", byteSize: " + length +
                 " }";
     }

test/jdk/java/foreign/TestByteBuffer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -260,6 +260,7 @@ public void testMappedSegmentOperations(MappedSegmentOp mappedBufferOp) throws T
         try (FileChannel fileChannel = FileChannel.open(f.toPath(), StandardOpenOption.READ, StandardOpenOption.WRITE)) {
             MemorySegment segment = fileChannel.map(FileChannel.MapMode.READ_WRITE, 0L, 8L, arena);
             assertTrue(segment.isMapped());
+            assertTrue(segment.toString().contains("mapped"));
             arena.close();
             mappedBufferOp.apply(segment);
         }

test/jdk/java/foreign/TestSegments.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -234,8 +234,10 @@ public void testToString(Supplier<MemorySegment> segmentSupplier) {
         assertTrue(s.contains("byteSize: "));
         if (segment.heapBase().isPresent()) {
             assertTrue(s.contains("heapBase: ["));
+            assertFalse(s.contains("native"));
         } else {
             assertFalse(s.contains("heapBase: "));
+            assertTrue(s.contains("native"));
         }
         assertFalse(s.contains("Optional"));
     }