JDK14/Java14源码在线阅读

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package javax.lang.model;

import java.util.Collections;
import java.util.Set;
import java.util.HashSet;

/**
 * Source versions of the Java™ programming language.
 *
 * See the appropriate edition of
 * <cite>The Java&trade; Language Specification</cite>
 * for information about a particular source version.
 *
 * <p>Note that additional source version constants will be added to
 * model future releases of the language.
 *
 * @author Joseph D. Darcy
 * @author Scott Seligman
 * @author Peter von der Ah&eacute;
 * @since 1.6
 */
public enum SourceVersion {
    /*
     * Summary of language evolution
     * 1.1: nested classes
     * 1.2: strictfp
     * 1.3: no changes
     * 1.4: assert
     * 1.5: annotations, generics, autoboxing, var-args...
     * 1.6: no changes
     * 1.7: diamond syntax, try-with-resources, etc.
     * 1.8: lambda expressions and default methods
     *   9: modules, small cleanups to 1.7 and 1.8 changes
     *  10: local-variable type inference (var)
     *  11: local-variable syntax for lambda parameters
     *  12: no changes (switch expressions in preview)
     *  13: no changes (switch expressions and text blocks in preview)
     *  14: switch expressions
     */

    /**
     * The original version.
     *
     * The language described in
     * <cite>The Java&trade; Language Specification, First Edition</cite>.
     */
    RELEASE_0,

    /**
     * The version recognized by the Java Platform 1.1.
     *
     * The language is {@code RELEASE_0} augmented with nested classes as described in the 1.1 update to
     * <cite>The Java&trade; Language Specification, First Edition</cite>.
     */
    RELEASE_1,

    /**
     * The version recognized by the Java 2 Platform, Standard Edition,
     * v 1.2.
     *
     * The language described in
     * <cite>The Java&trade; Language Specification,
     * Second Edition</cite>, which includes the {@code
     * strictfp} modifier.
     */
    RELEASE_2,

    /**
     * The version recognized by the Java 2 Platform, Standard Edition,
     * v 1.3.
     *
     * No major changes from {@code RELEASE_2}.
     */
    RELEASE_3,

    /**
     * The version recognized by the Java 2 Platform, Standard Edition,
     * v 1.4.
     *
     * Added a simple assertion facility.
     */
    RELEASE_4,

    /**
     * The version recognized by the Java 2 Platform, Standard
     * Edition 5.0.
     *
     * The language described in
     * <cite>The Java&trade; Language Specification,
     * Third Edition</cite>.  First release to support
     * generics, annotations, autoboxing, var-args, enhanced {@code
     * for} loop, and hexadecimal floating-point literals.
     */
    RELEASE_5,

    /**
     * The version recognized by the Java Platform, Standard Edition
     * 6.
     *
     * No major changes from {@code RELEASE_5}.
     */
    RELEASE_6,

    /**
     * The version recognized by the Java Platform, Standard Edition
     * 7.
     *
     * Additions in this release include, diamond syntax for
     * constructors, {@code try}-with-resources, strings in switch,
     * binary literals, and multi-catch.
     * @since 1.7
     */
    RELEASE_7,

    /**
     * The version recognized by the Java Platform, Standard Edition
     * 8.
     *
     * Additions in this release include lambda expressions and default methods.
     * @since 1.8
     */
    RELEASE_8,

    /**
     * The version recognized by the Java Platform, Standard Edition
     * 9.
     *
     * Additions in this release include modules and removal of a
     * single underscore from the set of legal identifier names.
     *
     * @since 9
     */
     RELEASE_9,

    /**
     * The version recognized by the Java Platform, Standard Edition
     * 10.
     *
     * Additions in this release include local-variable type inference
     * ({@code var}).
     *
     * @since 10
     */
     RELEASE_10,

    /**
     * The version recognized by the Java Platform, Standard Edition
     * 11.
     *
     * Additions in this release include local-variable syntax for
     * lambda parameters.
     *
     * @since 11
     */
     RELEASE_11,

    /**
     * The version recognized by the Java Platform, Standard Edition
     * 12.
     *
     * @since 12
     */
     RELEASE_12,

    /**
     * The version recognized by the Java Platform, Standard Edition
     * 13.
     *
     * @since 13
     */
     RELEASE_13,

    /**
     * The version recognized by the Java Platform, Standard Edition
     * 14.
     *
     * Additions in this release include switch expressions.
     *
     * @since 14
     */
     RELEASE_14;

    // Note that when adding constants for newer releases, the
    // behavior of latest() and latestSupported() must be updated too.

    /**
     * Returns the latest source version that can be modeled.
     *
     * @return the latest source version that can be modeled
     */
    public static SourceVersion latest() {
        return RELEASE_14;
    }

    private static final SourceVersion latestSupported = getLatestSupported();

    /*
     * The integer version to enum constant mapping implemented by
     * this method assumes the JEP 322: "Time-Based Release
     * Versioning" scheme is in effect. This scheme began in JDK
     * 10. If the JDK versioning scheme is revised, this method may
     * need to be updated accordingly.
     */
    private static SourceVersion getLatestSupported() {
        int intVersion = Runtime.version().feature();
        return (intVersion >= 11) ?
            valueOf("RELEASE_" + Math.min(14, intVersion)):
            RELEASE_10;
    }

    /**
     * Returns the latest source version fully supported by the
     * current execution environment.  {@code RELEASE_9} or later must
     * be returned.
     *
     * @apiNote This method is included alongside {@link latest} to
     * allow identification of situations where the language model API
     * is running on a platform version different than the latest
     * version modeled by the API. One way that sort of situation can
     * occur is if an IDE or similar tool is using the API to model
     * source version <i>N</i> while running on platform version
     * (<i>N</i>&nbsp;-&nbsp;1). Running in this configuration is
     * supported by the API. Running an API on platform versions
     * earlier than (<i>N</i>&nbsp;-&nbsp;1) or later than <i>N</i>
     * may or may not work as an implementation detail. If an
     * annotation processor was generating code to run under the
     * current execution environment, the processor should only use
     * platform features up to the {@code latestSupported} release,
     * which may be earlier than the {@code latest} release.
     *
     * @return the latest source version that is fully supported
     */
    public static SourceVersion latestSupported() {
        return latestSupported;
    }

    /**
     * Returns whether or not {@code name} is a syntactically valid
     * identifier (simple name) or keyword in the latest source
     * version.  The method returns {@code true} if the name consists
     * of an initial character for which {@link
     * Character#isJavaIdentifierStart(int)} returns {@code true},
     * followed only by characters for which {@link
     * Character#isJavaIdentifierPart(int)} returns {@code true}.
     * This pattern matches regular identifiers, keywords, restricted
     * keywords, restricted identifiers and the literals {@code "true"},
     * {@code "false"}, {@code "null"}.
     *
     * The method returns {@code false} for all other strings.
     *
     * @param name the string to check
     * @return {@code true} if this string is a
     * syntactically valid identifier or keyword, {@code false}
     * otherwise.
     */
    public static boolean isIdentifier(CharSequence name) {
        String id = name.toString();

        if (id.length() == 0) {
            return false;
        }
        int cp = id.codePointAt(0);
        if (!Character.isJavaIdentifierStart(cp)) {
            return false;
        }
        for (int i = Character.charCount(cp);
                i < id.length();
                i += Character.charCount(cp)) {
            cp = id.codePointAt(i);
            if (!Character.isJavaIdentifierPart(cp)) {
                return false;
            }
        }
        return true;
    }

    /**
     * Returns whether or not {@code name} is a syntactically valid
     * qualified name in the latest source version.  Unlike {@link
     * #isIdentifier isIdentifier}, this method returns {@code false}
     * for keywords, boolean literals, and the null literal.
     *
     * This method returns {@code true} for <i>restricted
     * keywords</i> and <i>restricted identifiers</i>
     *
     * @param name the string to check
     * @return {@code true} if this string is a
     * syntactically valid name, {@code false} otherwise.
     * @jls 3.9 Keywords
     * @jls 6.2 Names and Identifiers
     */
    public static boolean isName(CharSequence name) {
        return isName(name, latest());
    }

    /**
     * Returns whether or not {@code name} is a syntactically valid
     * qualified name in the given source version.  Unlike {@link
     * #isIdentifier isIdentifier}, this method returns {@code false}
     * for keywords, boolean literals, and the null literal.
     *
     * This method returns {@code true} for <i>restricted
     * keywords</i> and <i>restricted identifiers</i>
     *
     * @param name the string to check
     * @param version the version to use
     * @return {@code true} if this string is a
     * syntactically valid name, {@code false} otherwise.
     * @jls 3.9 Keywords
     * @jls 6.2 Names and Identifiers
     * @since 9
     */
    public static boolean isName(CharSequence name, SourceVersion version) {
        String id = name.toString();

        for(String s : id.split("\\.", -1)) {
            if (!isIdentifier(s) || isKeyword(s, version))
                return false;
        }
        return true;
    }

    /**
     * Returns whether or not {@code s} is a keyword, boolean literal,
     * or null literal in the latest source version.
     * This method returns {@code false} for <i>restricted
     * keywords</i> and <i>restricted identifiers</i>.
     *
     * @param s the string to check
     * @return {@code true} if {@code s} is a keyword, or boolean
     * literal, or null literal, {@code false} otherwise.
     * @jls 3.9 Keywords
     * @jls 3.10.3 Boolean Literals
     * @jls 3.10.7 The Null Literal
     */
    public static boolean isKeyword(CharSequence s) {
        return isKeyword(s, latest());
    }

    /**
     * Returns whether or not {@code s} is a keyword, boolean literal,
     * or null literal in the given source version.
     * This method returns {@code false} for <i>restricted
     * keywords</i> and <i>restricted identifiers</i>.
     *
     * @param s the string to check
     * @param version the version to use
     * @return {@code true} if {@code s} is a keyword, or boolean
     * literal, or null literal, {@code false} otherwise.
     * @jls 3.9 Keywords
     * @jls 3.10.3 Boolean Literals
     * @jls 3.10.7 The Null Literal
     * @since 9
     */
    public static boolean isKeyword(CharSequence s, SourceVersion version) {
        String id = s.toString();
        switch(id) {
            // A trip through history
        case "strictfp":
            return version.compareTo(RELEASE_2) >= 0;

        case "assert":
            return version.compareTo(RELEASE_4) >= 0;

        case "enum":

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