JDK 16 RFR of JDK-8250213: Address use of default constructors in com.sun.source.util

[Joe Darcy]

Hello,

Please review the webrev and CSR to address:

     JDK-8250213: Address use of default constructors in com.sun.source.util
     webrev: http://cr.openjdk.java.net/~darcy/8250213.0/
     CSR: https://bugs.openjdk.java.net/browse/JDK-8250215

For the com.sun.source classes, I add the previous implicit public 
no-arg constructors as all those classes look to intend to allow 
instantiation of themselves or of subclasses. For 
com.sun.tools.javac.Main, the constructor seems unintended as all the 
members of the class are static.

Patch below; before pushed, I'll update the copyright years, etc.

Thanks,

-Joe

--- 
old/src/jdk.compiler/share/classes/com/sun/source/util/DocTreePathScanner.java 
2020-07-23 09:48:38.498747851 -0700
+++ 
new/src/jdk.compiler/share/classes/com/sun/source/util/DocTreePathScanner.java 
2020-07-23 09:48:38.082955836 -0700
@@ -39,6 +39,11 @@
   */
  public class DocTreePathScanner<R, P> extends DocTreeScanner<R, P> {
      /**
+     * Constructor for subclasses to call.
+     */
+    public DocTreePathScanner() {}
+
+    /**
       * Scans a tree from a position identified by a tree path.
       * @param path the path
       * @param p a value to be passed to visitor methods
--- 
old/src/jdk.compiler/share/classes/com/sun/source/util/DocTreeScanner.java 
2020-07-23 09:48:39.330331881 -0700
+++ 
new/src/jdk.compiler/share/classes/com/sun/source/util/DocTreeScanner.java 
2020-07-23 09:48:38.886553865 -0700
@@ -68,6 +68,10 @@
   * @since 1.8
   */
  public class DocTreeScanner<R,P> implements DocTreeVisitor<R,P> {
+    /**
+     * Constructor for subclasses to call.
+     */
+    public DocTreeScanner() {}

      /**
       * Scans a single node.
--- old/src/jdk.compiler/share/classes/com/sun/source/util/DocTrees.java 
2020-07-23 09:48:40.109941910 -0700
+++ new/src/jdk.compiler/share/classes/com/sun/source/util/DocTrees.java 
2020-07-23 09:48:39.682155894 -0700
@@ -47,6 +47,11 @@
   */
  public abstract class DocTrees extends Trees {
      /**
+     * Constructor for subclasses to call.
+     */
+    public DocTrees() {}
+
+    /**
       * Returns a DocTrees object for a given CompilationTask.
       * @param task the compilation task for which to get the Trees object
       * @return the DocTrees object
--- 
old/src/jdk.compiler/share/classes/com/sun/source/util/JavacTask.java 
2020-07-23 09:48:40.873559937 -0700
+++ 
new/src/jdk.compiler/share/classes/com/sun/source/util/JavacTask.java 
2020-07-23 09:48:40.441775922 -0700
@@ -50,6 +50,10 @@
   * @since 1.6
   */
  public abstract class JavacTask implements CompilationTask {
+    /**
+     * Constructor for subclasses to call.
+     */
+    public JavacTask() {}

      /**
       * Returns the {@code JavacTask} for a {@code ProcessingEnvironment}.
--- 
old/src/jdk.compiler/share/classes/com/sun/source/util/TreePathScanner.java 
2020-07-23 09:48:41.721135968 -0700
+++ 
new/src/jdk.compiler/share/classes/com/sun/source/util/TreePathScanner.java 
2020-07-23 09:48:41.257367951 -0700
@@ -43,6 +43,10 @@
   * @since 1.6
   */
  public class TreePathScanner<R, P> extends TreeScanner<R, P> {
+    /**
+     * Constructor for subclasses to call.
+     */
+    public TreePathScanner() {}

      /**
       * Scans a tree from a position identified by a TreePath.
--- 
old/src/jdk.compiler/share/classes/com/sun/source/util/TreeScanner.java 
2020-07-23 09:48:42.564713999 -0700
+++ 
new/src/jdk.compiler/share/classes/com/sun/source/util/TreeScanner.java 
2020-07-23 09:48:42.100945982 -0700
@@ -75,6 +75,10 @@
   * @since 1.6
   */
  public class TreeScanner<R,P> implements TreeVisitor<R,P> {
+    /**
+     * Constructor for subclasses to call.
+     */
+    public TreeScanner() {}

      /**
       * Scans a single node.
--- old/src/jdk.compiler/share/classes/com/sun/source/util/Trees.java 
2020-07-23 09:48:43.408292029 -0700
+++ new/src/jdk.compiler/share/classes/com/sun/source/util/Trees.java 
2020-07-23 09:48:43.012490015 -0700
@@ -53,6 +53,11 @@
   */
  public abstract class Trees {
      /**
+     * Constructor for subclasses to call.
+     */
+    public Trees() {}
+
+    /**
       * Returns a Trees object for a given CompilationTask.
       * @param task the compilation task for which to get the Trees object
       * @throws IllegalArgumentException if the task does not support 
the Trees API.
--- old/src/jdk.compiler/share/classes/com/sun/tools/javac/Main.java 
2020-07-23 09:48:44.231880059 -0700
+++ new/src/jdk.compiler/share/classes/com/sun/tools/javac/Main.java 
2020-07-23 09:48:43.812090044 -0700
@@ -34,6 +34,8 @@
   * module for details on replacement APIs.
   */
  public class Main {
+    @Deprecated(since="16", forRemoval=true)
+    public Main(){}

      /** Main entry point for the launcher.
       *  Note: This method calls System.exit.