Address reliance on default constructors in jdk.jdi

Summary

Replace several implicit default constructors of classes in the jdk.jdi module with explicit public no-arg constructors.

Problem

Replying on default constructors for a formal API is not recommended.

Solution

Replace the default constructors with equivalent explicit constructors.

Specification

--- old/src/jdk.jdi/share/classes/com/sun/jdi/Bootstrap.java    2020-07-27 13:24:06.454000000 -0700
+++ new/src/jdk.jdi/share/classes/com/sun/jdi/Bootstrap.java    2020-07-27 13:24:05.842000000 -0700
@@ -38,6 +38,11 @@
  */

 public class Bootstrap extends Object {
+    /**
+     * Do not call.
+     */
+    @Deprecated(since="16", forRemoval=true)
+    public Bootstrap() {}

     /**
      * Returns the virtual machine manager.
--- old/src/jdk.jdi/share/classes/com/sun/jdi/connect/spi/Connection.java   2020-07-27 13:24:07.506000000 -0700
+++ new/src/jdk.jdi/share/classes/com/sun/jdi/connect/spi/Connection.java   2020-07-27 13:24:06.878000000 -0700
@@ -55,6 +55,10 @@
  * @since 1.5
  */
 public abstract class Connection {
+    /**
+     * Constructor for subclasses to call.
+     */
+    public Connection() {}

     /**
      * Reads a packet from the target VM.
--- old/src/jdk.jdi/share/classes/com/sun/jdi/connect/spi/TransportService.java 2020-07-27 13:24:08.570000000 -0700
+++ new/src/jdk.jdi/share/classes/com/sun/jdi/connect/spi/TransportService.java 2020-07-27 13:24:07.934000000 -0700
@@ -79,6 +79,10 @@
  * @since 1.5
  */
 public abstract class TransportService {
+    /**
+     * Constructor for subclasses to call.
+     */
+    public TransportService() {}

     /**
      * Returns a name to identify the transport service.
@@ -98,6 +102,10 @@
      * The transport service capabilities.
      */
     public static abstract class Capabilities {
+   /**
+    * Constructor for subclasses to call.
+    */
+   public Capabilities() {}

         /**
          * Tells whether or not this transport service can support
@@ -229,6 +237,10 @@
      * service from listening on an address.
      */
     public static abstract class ListenKey {
+   /**
+    * Constructor for subclasses to call.
+    */
+   public ListenKey() {}

         /**
          * Returns a string representation of the listen key.