JDK-8374395 : Improve MemoryUsage.toString() and constructor error messages for better clarity

src/java.management/share/classes/java/lang/management/MemoryUsage.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2003, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2003, 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
@@ -244,11 +244,19 @@ public long getMax() {
      */
     public String toString() {
         StringBuilder buf = new StringBuilder();
-        buf.append("init = " + init + "(" + (init >> 10) + "K) ");
+        if (init == -1) {
+            buf.append("init = N/A ");
+        } else {
+            buf.append("init = " + init + "(" + (init >> 10) + "K) ");
+        }
         buf.append("used = " + used + "(" + (used >> 10) + "K) ");
         buf.append("committed = " + committed + "(" +
                    (committed >> 10) + "K) " );
-        buf.append("max = " + max + "(" + (max >> 10) + "K)");
+        if (max == -1) {
+            buf.append("max = N/A");
+        } else {
+            buf.append("max = " + max + "(" + (max >> 10) + "K)");
+        }
         return buf.toString();
     }
 

test/hotspot/jtreg/vmTestbase/nsk/monitoring/MemoryUsage/MemoryUsage/memoryusage001.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2004, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2004, 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

test/jdk/java/lang/management/MemoryUsage/ToStringTest.java

@@ -0,0 +1,87 @@
+/*
+ * Copyright (c) 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+import java.lang.management.MemoryUsage;
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+public class ToStringTest {
+
+    @Test
+    public void testInitUndefined() {
+        MemoryUsage mu = new MemoryUsage(-1, 1024, 2048, 4096);
+        String result = mu.toString();
+        assertTrue(result.contains("init = N/A"),
+                   "Should show 'init = N/A' for undefined init, but got: " + result);
+        assertFalse(result.contains("init = -1"),
+                    "Should not show 'init = -1' for undefined init, but got: " + result);
+    }
+
+    @Test
+    public void testMaxUndefined() {
+        MemoryUsage mu = new MemoryUsage(1024, 2048, 4096, -1);
+        String result = mu.toString();
+        assertTrue(result.contains("max = N/A"),
+                   "Should show 'max = N/A' for undefined max, but got: " + result);
+        assertFalse(result.contains("max = -1"),
+                    "Should not show 'max = -1' for undefined max, but got: " + result);
+    }
+
+    @Test
+    public void testBothUndefined() {
+        MemoryUsage mu = new MemoryUsage(-1, 1024, 2048, -1);
+        String result = mu.toString();
+        assertTrue(result.contains("init = N/A"),
+                   "Should show 'init = N/A' when both are undefined, but got: " + result);
+        assertTrue(result.contains("max = N/A"),
+                   "Should show 'max = N/A' when both are undefined, but got: " + result);
+        assertFalse(result.contains("init = -1") || result.contains("max = -1"),
+                    "Should not show '-1' for undefined values, but got: " + result);
+    }
+
+    @Test
+    public void testAllValid() {
+        MemoryUsage mu = new MemoryUsage(1024, 2048, 4096, 8192);
+        String result = mu.toString();
+        assertTrue(result.contains("init = 1024"),
+                   "Should show init value for valid init, but got: " + result);
+        assertTrue(result.contains("used = 2048"),
+                   "Should show used value, but got: " + result);
+        assertTrue(result.contains("committed = 4096"),
+                   "Should show committed value, but got: " + result);
+        assertTrue(result.contains("max = 8192"),
+                   "Should show max value for valid max, but got: " + result);
+        assertFalse(result.contains("N/A"),
+                    "Should not show 'N/A' for valid values, but got: " + result);
+    }
+
+    @Test
+    public void testZeroValues() {
+        MemoryUsage mu = new MemoryUsage(0, 0, 0, 0);
+        String result = mu.toString();
+        assertTrue(result.contains("init = 0") && result.contains("used = 0") &&
+                   result.contains("committed = 0") && result.contains("max = 0"),
+                   "Should show zero values correctly, but got: " + result);
+    }
+}
+