src/java.base/share/classes/sun/reflect/generics/reflectiveObjects/ParameterizedTypeImpl.java

@@ -31,10 +31,11 @@
 import java.lang.reflect.Method;
 import java.lang.reflect.ParameterizedType;
 import java.lang.reflect.Type;
 import java.lang.reflect.TypeVariable;
 import java.util.Arrays;
+import java.util.StringJoiner;
 import java.util.Objects;
 
 /** Implementing class for ParameterizedType interface. */
 
 public class ParameterizedTypeImpl implements ParameterizedType {

@@ -205,14 +206,11 @@
 
     public String toString() {
         StringBuilder sb = new StringBuilder();
 
         if (ownerType != null) {
-            if (ownerType instanceof Class)
-                sb.append(((Class)ownerType).getName());
-            else
-                sb.append(ownerType.toString());
+            sb.append(ownerType.getTypeName());
 
             sb.append(".");
 
             if (ownerType instanceof ParameterizedTypeImpl) {
                 // Find simple name of nested type by removing the

@@ -222,21 +220,17 @@
             } else
                 sb.append(rawType.getName());
         } else
             sb.append(rawType.getName());
 
-        if (actualTypeArguments != null &&
-            actualTypeArguments.length > 0) {
-            sb.append("<");
-            boolean first = true;
+        if (actualTypeArguments != null) {
+            StringJoiner sj = new StringJoiner(", ", "<", ">");
+            sj.setEmptyValue("");
             for(Type t: actualTypeArguments) {
-                if (!first)
-                    sb.append(", ");
-                sb.append(t.getTypeName());
-                first = false;
+                sj.add(t.getTypeName());
             }
-            sb.append(">");
+            sb.append(sj.toString());
         }
 
         return sb.toString();
     }
 }