8280168: Add Objects.toIdentityString

Reviewed-by: alanb, mchung, rriggs, smarks

Author: jddarcy

src/java.base/share/classes/java/lang/invoke/MethodHandleProxies.java

@@ -292,7 +292,7 @@ private static boolean isObjectMethod(Method m) {
     private static Object callObjectMethod(Object self, Method m, Object[] args) {
         assert(isObjectMethod(m)) : m;
         return switch (m.getName()) {
-            case "toString" -> self.getClass().getName() + "@" + Integer.toHexString(self.hashCode());
+            case "toString" -> java.util.Objects.toIdentityString(self);
             case "hashCode" -> System.identityHashCode(self);
             case "equals"   -> (self == args[0]);
             default -> null;

src/java.base/share/classes/java/util/Objects.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2009, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2009, 2022, 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
@@ -164,6 +164,30 @@ public static String toString(Object o, String nullDefault) {
         return (o != null) ? o.toString() : nullDefault;
     }
 
+    /**
+     * {@return a string equivalent to the string returned by {@code
+     * Object.toString} if that method and {@code hashCode} are not
+     * overridden}
+     *
+     * @implNote
+     * This method constructs a string for an object without calling
+     * any overridable methods of the object.
+     *
+     * @implSpec
+     * The method returns a string equivalent to:<br>
+     * {@code o.getClass().getName() + "@" + Integer.toHexString(System.identityHashCode(o))}
+     *
+     * @param o an object
+     * @throws NullPointerException if the argument is null
+     * @see Object#toString
+     * @see System#identityHashCode(Object)
+     * @since 19
+     */
+    public static String toIdentityString(Object o) {
+        requireNonNull(o);
+        return o.getClass().getName() + "@" + Integer.toHexString(System.identityHashCode(o));
+    }
+
     /**
      * Returns 0 if the arguments are identical and {@code
      * c.compare(a, b)} otherwise.

test/jdk/java/util/Objects/BasicObjectsTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2009, 2015, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2009, 2022, 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
@@ -23,9 +23,8 @@
 
 /*
  * @test
- * @bug 6797535 6889858 6891113 8013712 8011800 8014365
+ * @bug 6797535 6889858 6891113 8013712 8011800 8014365 8280168
  * @summary Basic tests for methods in java.util.Objects
- * @author  Joseph D. Darcy
  */
 
 import java.util.*;
@@ -40,6 +39,7 @@ public static void main(String... args) {
         errors += testHash();
         errors += testToString();
         errors += testToString2();
+        errors += testToIdentityString();
         errors += testCompare();
         errors += testRequireNonNull();
         errors += testIsNull();
@@ -134,6 +134,37 @@ private static int testToString2() {
         return errors;
     }
 
+    private static int testToIdentityString() {
+        int errors = 0;
+        // Test null behavior
+        try {
+            Objects.toIdentityString(null);
+            errors++;
+        } catch (NullPointerException npe) {
+            ; // Expected
+        }
+        // Behavior on typical objects
+        Object o = new Object(){};
+        errors += (Objects.toIdentityString(o).equals(o.toString()))? 0 : 1;
+        // Verify object's toString *not* called
+        Object badToString = new Object() {
+                @Override
+                public String toString() {
+                    throw new RuntimeException();
+                }
+            };
+        Objects.toIdentityString(badToString);
+        // Verify object's hashCode *not* called
+        Object badHashCode = new Object() {
+                @Override
+                public int hashCode() {
+                    throw new RuntimeException("0xDEADBEFF");
+                }
+            };
+        Objects.toIdentityString(badHashCode);
+        return errors;
+    }
+
     private static int testCompare() {
         int errors = 0;
         String[] values = {"e. e. cummings", "zzz"};