java.lang.reflect.Method.copyOf

[John Rose]

On Oct 14, 2015, at 3:38 AM, Remi Forax <forax at univ-mlv.fr> wrote:
> 
> Given that j.l.r.Method is mutable, the best way to have performance is too encapsulate it in a non mutable class, if possible.

OK, I'll bite.  Here's a way to make Method its own non-mutable encapsulation, a la List::set or (future feature) frozen arrays.

diff --git a/src/java.base/share/classes/java/lang/reflect/AccessibleObject.java b/src/java.base/share/classes/java/lang/reflect/AccessibleObject.java
--- a/src/java.base/share/classes/java/lang/reflect/AccessibleObject.java
+++ b/src/java.base/share/classes/java/lang/reflect/AccessibleObject.java
@@ -120,15 +120,36 @@
      *
      * @param flag the new value for the {@code accessible} flag
      * @throws SecurityException if the request is denied.
+     * @throws UnsupportedOperationException if the accessible object is frozen
      * @see SecurityManager#checkPermission
      * @see java.lang.RuntimePermission
      */
-    public void setAccessible(boolean flag) throws SecurityException {
+    public void setAccessible(boolean flag) throws SecurityException, UnsupportedOperationException {
+        checkFrozen();
         SecurityManager sm = System.getSecurityManager();
         if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
         setAccessible0(this, flag);
     }
 
+    protected void checkFrozen() {
+        if (frozen)  throw new UnsupportedOperationException();
+    }
+
+    /**
+     * Make a frozen copy of this accessible object, with the accessible
+     * bit set to false.  If this object is already frozen, return the
+     * same object.  If this object is not already frozen, return a frozen
+     * copy, with the accessibility flag forced to {@code false}.
+     */
+    public abstract AccessibleObject asNonAccessible();
+
+    /**
+     * Return {@code true} if this object was produced by {@link #isNonAccessible}.
+     */
+    public boolean isNonAccessible() {
+        return frozen;
+    }
+
     /* Check that you aren't exposing java.lang.Class.<init> or sensitive
        fields in java.lang.Class. */
     private static void setAccessible0(AccessibleObject obj, boolean flag)
@@ -166,6 +187,9 @@
     // outside this package.
     boolean override;
 
+    // Indicates whether this object is frozen in the non-accessible state.
+    boolean frozen;
+
     // Reflection factory used by subclasses for creating field,
     // method, and constructor accessors. Note that this is called
     // very early in the bootstrapping process.