修饰器 Modifier

Java 中常见的修饰器：public、private、protected、static、final、…等等。

Java中的属性、方法、构造器、内部类等等都需要使用修饰器进行修饰，所以通过反射可以获取对应的Field对象、Method对象、等等。

Modifier的源码：

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package java.lang.reflect;

import java.security.AccessController;
import sun.reflect.ReflectionFactory;
import sun.reflect.ReflectionFactory.GetReflectionFactoryAction;

public class Modifier {
  public static final int PUBLIC = 1;
  public static final int PRIVATE = 2;
  public static final int PROTECTED = 4;
  public static final int STATIC = 8;
  public static final int FINAL = 16;
  public static final int SYNCHRONIZED = 32;
  public static final int VOLATILE = 64;
  public static final int TRANSIENT = 128;
  public static final int NATIVE = 256;
  public static final int INTERFACE = 512;
  public static final int ABSTRACT = 1024;
  public static final int STRICT = 2048;
  static final int BRIDGE = 64;
  static final int VARARGS = 128;
  static final int SYNTHETIC = 4096;
  static final int ANNOTATION = 8192;
  static final int ENUM = 16384;
  static final int MANDATED = 32768;
  private static final int CLASS_MODIFIERS = 3103;
  private static final int INTERFACE_MODIFIERS = 3087;
  private static final int CONSTRUCTOR_MODIFIERS = 7;
  private static final int METHOD_MODIFIERS = 3391;
  private static final int FIELD_MODIFIERS = 223;
  private static final int PARAMETER_MODIFIERS = 16;
  static final int ACCESS_MODIFIERS = 7;

  public Modifier() {
  }

  public static boolean isPublic(int var0) {
    return (var0 & 1) != 0;
  }

  public static boolean isPrivate(int var0) {
    return (var0 & 2) != 0;
  }

  public static boolean isProtected(int var0) {
    return (var0 & 4) != 0;
  }

  public static boolean isStatic(int var0) {
    return (var0 & 8) != 0;
  }

  public static boolean isFinal(int var0) {
    return (var0 & 16) != 0;
  }

  public static boolean isSynchronized(int var0) {
    return (var0 & 32) != 0;
  }

  public static boolean isVolatile(int var0) {
    return (var0 & 64) != 0;
  }

  public static boolean isTransient(int var0) {
    return (var0 & 128) != 0;
  }

  public static boolean isNative(int var0) {
    return (var0 & 256) != 0;
  }

  public static boolean isInterface(int var0) {
    return (var0 & 512) != 0;
  }

  public static boolean isAbstract(int var0) {
    return (var0 & 1024) != 0;
  }

  public static boolean isStrict(int var0) {
    return (var0 & 2048) != 0;
  }

  static boolean isSynthetic(int var0) {
    return (var0 & 4096) != 0;
  }

  static boolean isMandated(int var0) {
    return (var0 & '耀') != 0;
  }

  public static int classModifiers() {
    return 3103;
  }

  public static int interfaceModifiers() {
    return 3087;
  }

  public static int constructorModifiers() {
    return 7;
  }

  public static int methodModifiers() {
    return 3391;
  }

  public static int fieldModifiers() {
    return 223;
  }

  public static int parameterModifiers() {
    return 16;
  }
  ...
}

从源码可以看出，修饰器中的针对公共常量的处理采用了二进制枚举的思想。

Java实例中的属性或者方法的修饰器都由JVM控制，在其对应的Field对象、Method对象、Constructor对象等等，其内部都维护了一个private int modifiers;属性值，用于记录修饰器的类型。

根据二进制枚举的思想，将所有的修饰器的值都累加到modifiers属性值上，判断是否包含某种修饰器时，也是通过位运算实现，效率极高。

二进制枚举请见博文：二进制枚举/位枚举