Java枚举之EnumSet详解

private final static int FIRST = 1;
private final static int SECOND = 1 << 1;
private final static int THIRD = 1 << 2;

public enum EnumTest {
    FIRST,
    SECOND;
    public static void main(String[] args) {
        EnumSet<EnumTest> enumTests = EnumSet.allOf(EnumTest.class);
        //输出enumTests所有元素
        System.out.println(enumTests);//[FIRST, SECOND]
        //判断集中中是否存在
        System.out.println(enumTests.contains(EnumTest.SECOND));//true
    }
}

final Class<E> elementType;
final Enum<?>[] universe;

public static <E extends Enum<E>> EnumSet<E> noneOf(Class<E> elementType) {
        Enum<?>[] universe = getUniverse(elementType);//获取枚举类型的所有实例
        if (universe == null)
            throw new ClassCastException(elementType + " not an enum");
        if (universe.length <= 64)//判断枚举实例的数目
            return new RegularEnumSet<>(elementType, universe);
        else
            return new JumboEnumSet<>(elementType, universe);
    }

public static <E extends Enum<E>> EnumSet<E> allOf(Class<E> elementType) {
        EnumSet<E> result = noneOf(elementType);
        result.addAll();
        return result;
    }

//RegularEnumSet.java
private long elements = 0L;
void addAll() {
        if (universe.length != 0)
            elements = -1L >>> -universe.length;
}

public static <E extends Enum<E>> EnumSet<E> of(E e) {
        EnumSet<E> result = noneOf(e.getDeclaringClass());
        result.add(e);
        return result;
    }

public enum EnumTest {
    FIRST {
        @Override
        void doSometing() {
        }
    },
    SECOND {
        @Override
        void doSometing() {
        }
    };
    abstract void doSometing();
    public static void main(String[] args) {
        System.out.println(EnumTest.SECOND.getClass());//EnumTest$2
        System.out.println(EnumTest.SECOND.getDeclaringClass());//EnumTest
    }
}

public final Class<E> getDeclaringClass() {
        Class<?> clazz = getClass();//获取自己的Class
        Class<?> zuper = clazz.getSuperclass();//获取父类的Class
        return (zuper == Enum.class) ? (Class<E>)clazz : (Class<E>)zuper;//两者不等时取父类
    }

//RegularEnumSet.java
public boolean add(E e) {
        typeCheck(e);//校验e的类型是否和生成elementType一致
        long oldElements = elements;
        elements |= (1L << ((Enum<?>)e).ordinal());
        return elements != oldElements;
    }
 

//RegularEnumSet.java
public boolean contains(Object e) {
        if (e == null)//判空
            return false;
        Class<?> eClass = e.getClass();//校验类型
        if (eClass != elementType && eClass.getSuperclass() != elementType)
            return false;
        //比特位运算
        return (elements & (1L << ((Enum<?>)e).ordinal())) != 0;
    }