6521141: DebugGraphics NPE @ setFont();

Reviewed-by: prr

src/java.desktop/share/classes/javax/swing/DebugGraphics.java

@@ -27,6 +27,8 @@ package javax.swing;
 
 import java.awt.*;
 import java.awt.image.*;
+import java.security.AccessController;
+import java.security.PrivilegedAction;
 import java.text.AttributedCharacterIterator;
 
 /**
@@ -72,11 +74,32 @@ public class DebugGraphics extends Graphics {
     /**
      * Constructs a new debug graphics context that supports slowed
      * down drawing.
+     * <p>
+     * NOTE: This constructor should not be called by
+     * applications, it is for internal use only. When called directly
+     * it will create an un-usable instance.
      */
+    @SuppressWarnings("removal")
     public DebugGraphics() {
         super();
         buffer = null;
         xOffset = yOffset = 0;
+
+        //  Creates a Graphics context when the constructor is called.
+        if (this.graphics == null) {
+            StackWalker walker = AccessController.doPrivileged(new PrivilegedAction<StackWalker>() {
+                @Override
+                public StackWalker run() {
+                    StackWalker stackwalker = StackWalker.getInstance(StackWalker.Option.RETAIN_CLASS_REFERENCE);
+                    return stackwalker;
+                }
+            });
+
+            if (walker.getCallerClass() != this.getClass()) {
+                BufferedImage bi = new BufferedImage(1, 1, BufferedImage.TYPE_INT_RGB);
+                this.graphics = bi.createGraphics();
+            }
+        }
     }
 
     /**

test/jdk/javax/swing/DebugGraphics/DebugGraphicsNPETest.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 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
+ * 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.awt.Font;
+import javax.swing.DebugGraphics;
+
+/* @test
+ * @bug 6521141
+ * @summary Test to check if NPE does not occur when graphics is not
+ *  initialized and DebugGraphics instance is created with default
+ *  Constructor and used.
+ * @run main DebugGraphicsNPETest
+ */
+public class DebugGraphicsNPETest {
+    public static void main(String[] args) throws Exception {
+        DebugGraphics dg = new DebugGraphics();
+        Font font = new Font(Font.SERIF, Font.PLAIN, 10);
+        dg.setFont(font);
+        System.out.println("Test Pass!");
+    }
+}