--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/jdk.jshell/share/classes/jdk/internal/jshell/tool/PersistentStorage.java	Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,104 @@
+/*
+ * Copyright (c) 2016, 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.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * 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.
+ */
+
+package jdk.internal.jshell.tool;
+
+/**
+ * The required functionality jshell uses for persistent storage.  Implementable
+ * by both Preferences API and Map.
+ */
+interface PersistentStorage {
+
+    /**
+     * Removes all of the preferences (key-value associations) in
+     * preferences.
+     *
+     * @throws IllegalStateException if this operation cannot be completed
+     * because of the state of the system.
+     */
+    void clear();
+
+    /**
+     * Returns all of the keys that have an associated value in
+     * preferences.
+     *
+     * @return an array of the keys that have an associated value in this
+     * preference node.
+     * @throws IllegalStateException if this operation cannot be completed
+     * because of the state of the system.
+     */
+    String[] keys();
+
+    /**
+     * Returns the value associated with the specified key in preferences.
+     *
+     * @param key key whose associated value is to be returned.
+     * @return the value associated with {@code key}, or {@code null} if no
+     * value is associated with {@code key}.
+     * @throws IllegalStateException if this operation cannot be completed
+     * because of the state of the system.
+     * @throws NullPointerException if {@code key} is {@code null}.
+     */
+    String get(String key);
+
+    /**
+     * Associates the specified value with the specified key in this
+     * preference node.
+     *
+     * @param key key with which the specified value is to be associated.
+     * @param value value to be associated with the specified key.
+     * @throws NullPointerException if key or value is {@code null}.
+     * @throws IllegalArgumentException if key or value are too long.
+     * @throws IllegalStateException if this operation cannot be completed
+     * because of the state of the system.
+     */
+    void put(String key, String value);
+
+    /**
+     * Removes the value associated with the specified key in preferences,
+     * if any.
+     *
+     * @param key key whose mapping is to be removed from the preference
+     * node.
+     * @throws NullPointerException if {@code key} is {@code null}.
+     * @throws IllegalStateException if this operation cannot be completed
+     * because of the state of the system.
+     */
+    void remove(String key);
+
+    /**
+     * Forces any changes in the contents of this preferences to be stored.
+     * Once this method returns successfully, it is safe to assume that all
+     * changes have become as permanent as they are going to be.
+     * <p>
+     * Implementations are free to flush changes into the persistent store
+     * at any time. They do not need to wait for this method to be called.
+     *
+     * @throws IllegalStateException if this operation cannot be completed
+     * because of the state of the system.
+     */
+    void flush();
+
+}