/** * @(#)Context.java	1.5 03/01/23 * * Copyright 2003 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */package com.sun.tools.javac.v8.util;/** * * Support for an abstract context, modelled loosely after ThreadLocal * but using a user-provided context instead of the current thread. * * Within the compiler, a single Context is used for each invocation of * the compiler.  The context is then used to ensure a single copy of * each compiler phase exists per compiler invocation. * * <p>Typical usage pattern is: * <pre> * public class Phase { *     private static final Context.Key<Phase> phaseKey = new Context.Key<Phase>(); * *     public static Phase instance(Context context) { *	   Phase instance = context.get(phaseKey); *	   if (instance == null) *	       instance = new Phase(context); *	   return instance; *     } * *     protected Phase(Context context) { *	   context.put(thaseKey, this); *	   // other intitialization follows... *     } * } * </pre> */public class Context {    /**     * The client creates an instance of this class for each key.     */    public static class Key {        public Key() {            super();        }    }    /**      *      * The underlying map storing the data.      * We maintain the invariant that this table contains only      * mappings of the form      *     Key<T> -> T      */    private Hashtable ht = Hashtable.make();    /**     * Set the value for the key in this context.     */    public void put(Key key, Object data) {        if (ht.put(key, data) != null)            throw new AssertionError("duplicate context value");    }    /**      * Get the value for the key in this context.      */    public Object get(Key key) {        return (Object) ht.get(key);    }    public Context() {        super();    }}