diff -r c7841bbe1227 -r 7ae6c0fd479b src/share/classes/com/sun/tools/javac/code/Type.java
--- a/src/share/classes/com/sun/tools/javac/code/Type.java	Thu Apr 28 08:46:06 2011 -0700
+++ b/src/share/classes/com/sun/tools/javac/code/Type.java	Thu Apr 28 15:05:36 2011 -0700
@@ -25,6 +25,8 @@
 
 package com.sun.tools.javac.code;
 
+import java.util.Collections;
+
 import com.sun.tools.javac.util.*;
 import com.sun.tools.javac.code.Symbol.*;
 
@@ -741,6 +743,38 @@
         }
     }
 
+    // a clone of a ClassType that knows about the alternatives of a union type.
+    public static class UnionClassType extends ClassType implements UnionType {
+        final List<? extends Type> alternatives_field;
+
+        public UnionClassType(ClassType ct, List<? extends Type> alternatives) {
+            super(ct.outer_field, ct.typarams_field, ct.tsym);
+            allparams_field = ct.allparams_field;
+            supertype_field = ct.supertype_field;
+            interfaces_field = ct.interfaces_field;
+            all_interfaces_field = ct.interfaces_field;
+            alternatives_field = alternatives;
+        }
+
+        public Type getLub() {
+            return tsym.type;
+        }
+
+        public java.util.List<? extends TypeMirror> getAlternatives() {
+            return Collections.unmodifiableList(alternatives_field);
+        }
+
+        @Override
+        public TypeKind getKind() {
+            return TypeKind.UNION;
+        }
+
+        @Override
+        public <R, P> R accept(TypeVisitor<R, P> v, P p) {
+            return v.visitUnion(this, p);
+        }
+    }
+
     public static class ArrayType extends Type
             implements javax.lang.model.type.ArrayType {