--- a/src/java.base/share/classes/java/net/URLStreamHandler.java	Thu May 16 17:09:11 2019 +0200
+++ b/src/java.base/share/classes/java/net/URLStreamHandler.java	Fri May 31 15:02:45 2019 +0100
@@ -76,9 +76,15 @@
      * support proxying will ignore the proxy parameter and make a
      * normal connection.
      *
-     * Calling this method preempts the system's default
+     * <p> Calling this method preempts the system's default
      * {@link java.net.ProxySelector ProxySelector} settings.
      *
+     * @implSpec
+     * The default implementation of this method first checks that the given
+     * {code URL} and {code Proxy} are not null, then throws {@code
+     * UnsupportedOperationException}. Subclasses should override this method
+     * with an appropriate implementation.
+     *
      * @param      u   the URL that this connects to.
      * @param      p   the proxy through which the connection will be made.
      *                 If direct connection is desired, Proxy.NO_PROXY
@@ -93,6 +99,8 @@
      * @since      1.5
      */
     protected URLConnection openConnection(URL u, Proxy p) throws IOException {
+        if (u == null || p == null)
+            throw new IllegalArgumentException("null " + (u == null ? "url" : "proxy"));
         throw new UnsupportedOperationException("Method not implemented.");
     }
 

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/jdk/java/net/URLStreamHandler/TestDefaultBehavior.java	Fri May 31 15:02:45 2019 +0100
@@ -0,0 +1,79 @@
+/*
+ * Copyright (c) 2019, 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.
+ */
+
+/*
+ * @test
+ * @bug 8224973
+ * @summary Basic test for the default behavior of openConnection(URL,Proxy)
+ * @run testng TestDefaultBehavior
+ */
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.net.Proxy;
+import java.net.URI;
+import java.net.URL;
+import java.net.URLConnection;
+import java.net.URLStreamHandler;
+import org.testng.annotations.Test;
+import static java.net.Proxy.*;
+import static org.testng.Assert.expectThrows;
+
+public class TestDefaultBehavior {
+
+    static final Class<IllegalArgumentException> IAE = IllegalArgumentException.class;
+    static final Class<UnsupportedOperationException> UOE = UnsupportedOperationException.class;
+
+    static final InetSocketAddress ADDR = InetSocketAddress.createUnresolved("proxy.com", 80);
+    static final URI uri = URI.create("http://example.com:80/");
+
+    @Test
+    public void testDefaultBehavior() {
+        CustomURLStreamHandler handler = new CustomURLStreamHandler();
+
+        expectThrows(IAE, () -> handler.openConnection(null, null));
+        expectThrows(IAE, () -> handler.openConnection(null, NO_PROXY));
+        expectThrows(IAE, () -> handler.openConnection(null, new Proxy(Type.SOCKS, ADDR)));
+        expectThrows(IAE, () -> handler.openConnection(null, new Proxy(Type.HTTP, ADDR)));
+        expectThrows(IAE, () -> handler.openConnection(uri.toURL(), null));
+
+        expectThrows(UOE, () -> handler.openConnection(uri.toURL(), NO_PROXY));
+        expectThrows(UOE, () -> handler.openConnection(uri.toURL(), new Proxy(Type.SOCKS, ADDR)));
+        expectThrows(UOE, () -> handler.openConnection(uri.toURL(), new Proxy(Type.HTTP, ADDR)));
+    }
+
+    // A URLStreamHandler that delegates the overloaded openConnection that
+    // takes a proxy, to the default java.net.URLStreamHandler implementation.
+    static class CustomURLStreamHandler extends URLStreamHandler {
+
+        @Override
+        public URLConnection openConnection(URL url, Proxy proxy) throws IOException {
+            return super.openConnection(url, proxy);
+        }
+
+        @Override
+        protected URLConnection openConnection(URL u) throws IOException {
+            return null;
+        }
+    }
+}