javac是sun公司开发人员使用java语言编写的优秀的工业级java编译器

				/**				 * @(#)Source.java	1.2 03/01/23				 *				 * Copyright 2003 Sun Microsystems, Inc. All Rights Reserved.				 *				 * This software is the proprietary information of Sun Microsystems, Inc.				 * Use is subject to license terms.				 *				 */				package com.sun.tools.javac.v8.code;				import com.sun.tools.javac.v8.util.*;												/**				 * The source language version accepted.				 */				public class Source {				    private static final Context.Key sourceKey = new Context.Key();								    public static Source instance(Context context) {				        Source instance = (Source) context.get(sourceKey);				        if (instance == null) {				            Options options = Options.instance(context);				            String sourceString = (String) options.get("-source");				            if (sourceString != null)				                instance = lookup(sourceString);				            if (instance == null)				                instance = DEFAULT;				            context.put(sourceKey, instance);				        }				        return instance;				    }				    private static int nextOrdinal = 0;				    private static final Hashtable tab = new Hashtable();				    public final int ordinal = nextOrdinal++;				    public final String name;								    private Source(String name) {				        super();				        this.name = name;				        tab.put(name, this);				    }								    /**				      * 1.2 introduced strictfp.				      */				    public static final Source JDK1_2 = new Source("1.2");								    /**				     * 1.3 is the same language as 1.2.				     */				    public static final Source JDK1_3 = new Source("1.3");								    /**				     * 1.4 introduced assert.				     */				    public static final Source JDK1_4 = new Source("1.4");				    public static final Source DEFAULT = JDK1_3;								    public static Source lookup(String name) {				        return (Source) tab.get(name);				    }				}