Modifier.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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package java.lang.reflect;

import jdk.internal.reflect.ReflectionFactory;

import java.security.AccessController;
import java.util.StringJoiner;

/**
 * The Modifier class provides {@code static} methods and
 * constants to decode class and member access modifiers.  The sets of
 * modifiers are represented as integers with distinct bit positions
 * representing different modifiers.  The values for the constants
 * representing the modifiers are taken from the tables in sections 4.1, 4.4, 4.5, and 4.7 of
 * <cite>The Java&trade; Virtual Machine Specification</cite>.
 *
 * @see Class#getModifiers()
 * @see Member#getModifiers()
 *
 * @author Nakul Saraiya
 * @author Kenneth Russell
 * @since 1.1
 */
// 类/接口/构造器/方法/字段上的修饰符
public class Modifier {
    
    /**
     * The {@code int} value representing the {@code public} modifier.
     */
    public static final int PUBLIC = 0x00000001;  // public
    
    /**
     * The {@code int} value representing the {@code private} modifier.
     */
    public static final int PRIVATE = 0x00000002;  // private
    
    /**
     * The {@code int} value representing the {@code protected} modifier.
     */
    public static final int PROTECTED = 0x00000004;  // protected
    
    /**
     * The {@code int} value representing the {@code static} modifier.
     */
    public static final int STATIC = 0x00000008;  // static
    
    /**
     * The {@code int} value representing the {@code final} modifier.
     */
    public static final int FINAL = 0x00000010;  // final
    
    /**
     * The {@code int} value representing the {@code synchronized} modifier.
     */
    public static final int SYNCHRONIZED = 0x00000020;  // synchronized
    
    /**
     * The {@code int} value representing the {@code volatile} modifier.
     */
    public static final int VOLATILE = 0x00000040;  // volatile
    
    /**
     * The {@code int} value representing the {@code transient} modifier.
     */
    public static final int TRANSIENT = 0x00000080;  // transient
    
    /**
     * The {@code int} value representing the {@code native} modifier.
     */
    public static final int NATIVE = 0x00000100;  // native
    
    /**
     * The {@code int} value representing the {@code interface} modifier.
     */
    public static final int INTERFACE = 0x00000200;  // interface
    
    /**
     * The {@code int} value representing the {@code abstract} modifier.
     */
    public static final int ABSTRACT = 0x00000400;  // abstract
    
    /**
     * The {@code int} value representing the {@code strictfp} modifier.
     */
    public static final int STRICT = 0x00000800;  // strictfp
    
    // Bits not (yet) exposed in the public API either because they
    // have different meanings for fields and methods and there is no
    // way to distinguish between the two in this class, or because
    // they are not Java programming language keywords
    static final int BRIDGE    = 0x00000040;
    static final int VARARGS   = 0x00000080;
    static final int SYNTHETIC = 0x00001000;
    static final int ANNOTATION  = 0x00002000;
    static final int ENUM      = 0x00004000;
    static final int MANDATED  = 0x00008000;
    
    
    /* Bootstrapping protocol between java.lang and java.lang.reflect packages */
    static {
        ReflectionFactory factory = AccessController.doPrivileged(new ReflectionFactory.GetReflectionFactoryAction());
        factory.setLangReflectAccess(new java.lang.reflect.ReflectAccess());
    }
    
    
    
    /*▼ 判断是否存在某种修饰符 ███████████████████████████████████████████████████████████████┓ */
    
    /**
     * Return {@code true} if the integer argument includes the
     * {@code public} modifier, {@code false} otherwise.
     *
     * @param   mod a set of modifiers
     * @return {@code true} if {@code mod} includes the
     * {@code public} modifier; {@code false} otherwise.
     */
    public static boolean isPublic(int mod) {
        return (mod & PUBLIC) != 0;
    }
    
    /**
     * Return {@code true} if the integer argument includes the
     * {@code private} modifier, {@code false} otherwise.
     *
     * @param   mod a set of modifiers
     * @return {@code true} if {@code mod} includes the
     * {@code private} modifier; {@code false} otherwise.
     */
    public static boolean isPrivate(int mod) {
        return (mod & PRIVATE) != 0;
    }
    
    /**
     * Return {@code true} if the integer argument includes the
     * {@code protected} modifier, {@code false} otherwise.
     *
     * @param   mod a set of modifiers
     * @return {@code true} if {@code mod} includes the
     * {@code protected} modifier; {@code false} otherwise.
     */
    public static boolean isProtected(int mod) {
        return (mod & PROTECTED) != 0;
    }
    
    /**
     * Return {@code true} if the integer argument includes the
     * {@code static} modifier, {@code false} otherwise.
     *
     * @param   mod a set of modifiers
     * @return {@code true} if {@code mod} includes the
     * {@code static} modifier; {@code false} otherwise.
     */
    public static boolean isStatic(int mod) {
        return (mod & STATIC) != 0;
    }
    
    /**
     * Return {@code true} if the integer argument includes the
     * {@code final} modifier, {@code false} otherwise.
     *
     * @param   mod a set of modifiers
     * @return {@code true} if {@code mod} includes the
     * {@code final} modifier; {@code false} otherwise.
     */
    public static boolean isFinal(int mod) {
        return (mod & FINAL) != 0;
    }
    
    /**
     * Return {@code true} if the integer argument includes the
     * {@code synchronized} modifier, {@code false} otherwise.
     *
     * @param   mod a set of modifiers
     * @return {@code true} if {@code mod} includes the
     * {@code synchronized} modifier; {@code false} otherwise.
     */
    public static boolean isSynchronized(int mod) {
        return (mod & SYNCHRONIZED) != 0;
    }
    
    /**
     * Return {@code true} if the integer argument includes the
     * {@code volatile} modifier, {@code false} otherwise.
     *
     * @param   mod a set of modifiers
     * @return {@code true} if {@code mod} includes the
     * {@code volatile} modifier; {@code false} otherwise.
     */
    public static boolean isVolatile(int mod) {
        return (mod & VOLATILE) != 0;
    }
    
    /**
     * Return {@code true} if the integer argument includes the
     * {@code transient} modifier, {@code false} otherwise.
     *
     * @param   mod a set of modifiers
     * @return {@code true} if {@code mod} includes the
     * {@code transient} modifier; {@code false} otherwise.
     */
    public static boolean isTransient(int mod) {
        return (mod & TRANSIENT) != 0;
    }
    
    /**
     * Return {@code true} if the integer argument includes the
     * {@code native} modifier, {@code false} otherwise.
     *
     * @param   mod a set of modifiers
     * @return {@code true} if {@code mod} includes the
     * {@code native} modifier; {@code false} otherwise.
     */
    public static boolean isNative(int mod) {
        return (mod & NATIVE) != 0;
    }
    
    /**
     * Return {@code true} if the integer argument includes the
     * {@code interface} modifier, {@code false} otherwise.
     *
     * @param   mod a set of modifiers
     * @return {@code true} if {@code mod} includes the
     * {@code interface} modifier; {@code false} otherwise.
     */
    public static boolean isInterface(int mod) {
        return (mod & INTERFACE) != 0;
    }
    
    /**
     * Return {@code true} if the integer argument includes the
     * {@code abstract} modifier, {@code false} otherwise.
     *
     * @param   mod a set of modifiers
     * @return {@code true} if {@code mod} includes the
     * {@code abstract} modifier; {@code false} otherwise.
     */
    public static boolean isAbstract(int mod) {
        return (mod & ABSTRACT) != 0;
    }
    
    /**
     * Return {@code true} if the integer argument includes the
     * {@code strictfp} modifier, {@code false} otherwise.
     *
     * @param   mod a set of modifiers
     * @return {@code true} if {@code mod} includes the
     * {@code strictfp} modifier; {@code false} otherwise.
     */
    public static boolean isStrict(int mod) {
        return (mod & STRICT) != 0;
    }
    
    static boolean isSynthetic(int mod) {
        return (mod & SYNTHETIC) != 0;
    }
    
    static boolean isMandated(int mod) {
        return (mod & MANDATED) != 0;
    }
    
    /*▲ 判断是否存在某种修饰符 ███████████████████████████████████████████████████████████████┛ */
    
    
    
    // Note on the FOO_MODIFIERS fields and fooModifiers() methods:
    // the sets of modifiers are not guaranteed to be constants
    // across time and Java SE releases. Therefore, it would not be
    // appropriate to expose an external interface to this information
    // that would allow the values to be treated as Java-level
    // constants since the values could be constant folded and updates
    // to the sets of modifiers missed. Thus, the fooModifiers()
    // methods return an unchanging values for a given release, but a
    // value that can potentially change over time.
    
    /**
     * The Java source modifiers that can be applied to a class.
     * @jls 8.1.1 Class Modifiers
     */
    // 类修饰符
    private static final int CLASS_MODIFIERS =
        Modifier.PUBLIC         | Modifier.PROTECTED    | Modifier.PRIVATE |
            Modifier.ABSTRACT       | Modifier.STATIC       | Modifier.FINAL   |
            Modifier.STRICT;
    
    /**
     * The Java source modifiers that can be applied to an interface.
     * @jls 9.1.1 Interface Modifiers
     */
    // 接口修饰符
    private static final int INTERFACE_MODIFIERS =
        Modifier.PUBLIC         | Modifier.PROTECTED    | Modifier.PRIVATE |
            Modifier.ABSTRACT       | Modifier.STATIC       | Modifier.STRICT;
    
    
    /**
     * The Java source modifiers that can be applied to a constructor.
     * @jls 8.8.3 Constructor Modifiers
     */
    // 构造器修饰符
    private static final int CONSTRUCTOR_MODIFIERS =
        Modifier.PUBLIC         | Modifier.PROTECTED    | Modifier.PRIVATE;
    
    /**
     * The Java source modifiers that can be applied to a method.
     * @jls8.4.3  Method Modifiers
     */
    // 方法修饰符
    private static final int METHOD_MODIFIERS =
        Modifier.PUBLIC         | Modifier.PROTECTED    | Modifier.PRIVATE |
            Modifier.ABSTRACT       | Modifier.STATIC       | Modifier.FINAL   |
            Modifier.SYNCHRONIZED   | Modifier.NATIVE       | Modifier.STRICT;
    
    /**
     * The Java source modifiers that can be applied to a field.
     * @jls 8.3.1  Field Modifiers
     */
    // 字段修饰符
    private static final int FIELD_MODIFIERS =
        Modifier.PUBLIC         | Modifier.PROTECTED    | Modifier.PRIVATE |
            Modifier.STATIC         | Modifier.FINAL        | Modifier.TRANSIENT |
            Modifier.VOLATILE;
    
    /**
     * The Java source modifiers that can be applied to a method or constructor parameter.
     * @jls 8.4.1 Formal Parameters
     */
    // 形参修饰符
    private static final int PARAMETER_MODIFIERS =
        Modifier.FINAL;
    
    /**
     *
     */
    // 访问控制修饰符
    static final int ACCESS_MODIFIERS =
        Modifier.PUBLIC | Modifier.PROTECTED | Modifier.PRIVATE;
    
    /**
     * Return an {@code int} value OR-ing together the source language
     * modifiers that can be applied to a class.
     *
     * @return an {@code int} value OR-ing together the source language
     * modifiers that can be applied to a class.
     *
     * @jls 8.1.1 Class Modifiers
     * @since 1.7
     */
    // 返回类修饰符
    public static int classModifiers() {
        return CLASS_MODIFIERS;
    }
    
    /**
     * Return an {@code int} value OR-ing together the source language
     * modifiers that can be applied to an interface.
     *
     * @return an {@code int} value OR-ing together the source language
     * modifiers that can be applied to an interface.
     *
     * @jls 9.1.1 Interface Modifiers
     * @since 1.7
     */
    // 返回接口修饰符
    public static int interfaceModifiers() {
        return INTERFACE_MODIFIERS;
    }
    
    /**
     * Return an {@code int} value OR-ing together the source language
     * modifiers that can be applied to a constructor.
     *
     * @return an {@code int} value OR-ing together the source language
     * modifiers that can be applied to a constructor.
     *
     * @jls 8.8.3 Constructor Modifiers
     * @since 1.7
     */
    // 返回构造器修饰符
    public static int constructorModifiers() {
        return CONSTRUCTOR_MODIFIERS;
    }
    
    /**
     * Return an {@code int} value OR-ing together the source language
     * modifiers that can be applied to a method.
     *
     * @return an {@code int} value OR-ing together the source language
     * modifiers that can be applied to a method.
     *
     * @jls 8.4.3 Method Modifiers
     * @since 1.7
     */
    // 返回方法修饰符
    public static int methodModifiers() {
        return METHOD_MODIFIERS;
    }
    
    /**
     * Return an {@code int} value OR-ing together the source language
     * modifiers that can be applied to a field.
     *
     * @return an {@code int} value OR-ing together the source language
     * modifiers that can be applied to a field.
     *
     * @jls 8.3.1 Field Modifiers
     * @since 1.7
     */
    // 返回字段修饰符
    public static int fieldModifiers() {
        return FIELD_MODIFIERS;
    }
    
    /**
     * Return an {@code int} value OR-ing together the source language
     * modifiers that can be applied to a parameter.
     *
     * @return an {@code int} value OR-ing together the source language
     * modifiers that can be applied to a parameter.
     *
     * @jls 8.4.1 Formal Parameters
     * @since 1.8
     */
    // 返回形参修饰符
    public static int parameterModifiers() {
        return PARAMETER_MODIFIERS;
    }
    
    
    
    /**
     * Return a string describing the access modifier flags in
     * the specified modifier. For example:
     * <blockquote><pre>
     *    public final synchronized strictfp
     * </pre></blockquote>
     * The modifier names are returned in an order consistent with the
     * suggested modifier orderings given in sections 8.1.1, 8.3.1, 8.4.3, 8.8.3, and 9.1.1 of
     * <cite>The Java&trade; Language Specification</cite>.
     * The full modifier ordering used by this method is:
     * <blockquote> {@code
     * public protected private abstract static final transient
     * volatile synchronized native strictfp
     * interface } </blockquote>
     * The {@code interface} modifier discussed in this class is
     * not a true modifier in the Java language and it appears after
     * all other modifiers listed by this method.  This method may
     * return a string of modifiers that are not valid modifiers of a
     * Java entity; in other words, no checking is done on the
     * possible validity of the combination of modifiers represented
     * by the input.
     *
     * Note that to perform such checking for a known kind of entity,
     * such as a constructor or method, first AND the argument of
     * {@code toString} with the appropriate mask from a method like
     * {@link #constructorModifiers} or {@link #methodModifiers}.
     *
     * @param   mod a set of modifiers
     * @return  a string representation of the set of modifiers
     * represented by {@code mod}
     */
    // 字符串化
    public static String toString(int mod) {
        StringJoiner sj = new StringJoiner(" ");
        
        if ((mod & PUBLIC) != 0)        sj.add("public");
        if ((mod & PROTECTED) != 0)     sj.add("protected");
        if ((mod & PRIVATE) != 0)       sj.add("private");
        
        /* Canonical order */
        if ((mod & ABSTRACT) != 0)      sj.add("abstract");
        if ((mod & STATIC) != 0)        sj.add("static");
        if ((mod & FINAL) != 0)         sj.add("final");
        if ((mod & TRANSIENT) != 0)     sj.add("transient");
        if ((mod & VOLATILE) != 0)      sj.add("volatile");
        if ((mod & SYNCHRONIZED) != 0)  sj.add("synchronized");
        if ((mod & NATIVE) != 0)        sj.add("native");
        if ((mod & STRICT) != 0)        sj.add("strictfp");
        if ((mod & INTERFACE) != 0)     sj.add("interface");
        
        return sj.toString();
    }
    
}