标签：nali lan 结果 ack des static java odata 用法
jvm并不支持枚举类型，java中枚举类型是在编译器层面上实现的，先看如下代码:
package demo.nio; public class EnumDemo { public static enum Color{ Red(20), Green(10), Blue(30); Color(int v){ this.value = v; } private int value; public int getValue(){ return this.value; } } public static void main(String[] args) { System.out.println(Color.class.getSuperclass()); } }
输出结果:class java.lang.Enum
也就是说所有的枚举类型都是 java.lang.Enum的直接子类，java.lang.Enum是个抽象类，内部两个字段，ordinal和name，代码如下:
package java.lang; import java.io.Serializable; import java.io.IOException; import java.io.InvalidObjectException; import java.io.ObjectInputStream; import java.io.ObjectStreamException; public abstract class Enum<E extends Enum<E>> implements Comparable<E>, Serializable { private final String name; public final String name() { return name; } private final int ordinal; public final int ordinal() { return ordinal; } protected Enum(String name, int ordinal) { this.name = name; this.ordinal = ordinal; } public String toString() { return name; } public final boolean equals(Object other) { return this==other; } public final int hashCode() { return super.hashCode(); } protected final Object clone() throws CloneNotSupportedException { throw new CloneNotSupportedException(); } public final int compareTo(E o) { Enum other = (Enum)o; Enum self = this; if (self.getClass() != other.getClass() &&self.getDeclaringClass() != other.getDeclaringClass()) throw new ClassCastException(); return self.ordinal - other.ordinal; } public final Class<E> getDeclaringClass() { Class clazz = getClass(); Class zuper = clazz.getSuperclass(); return (zuper == Enum.class) ? clazz : zuper; } public static <T extends Enum<T>> T valueOf(Class<T> enumType,String name) { T result = enumType.enumConstantDirectory().get(name); if (result != null) return result; if (name == null) throw new NullPointerException("Name is null"); throw new IllegalArgumentException( "No enum constant " + enumType.getCanonicalName() + "." + name); } protected final void finalize() { } private void readObject(ObjectInputStream in) throws IOException,ClassNotFoundException { throw new InvalidObjectException("can‘t deserialize enum"); } private void readObjectNoData() throws ObjectStreamException { throw new InvalidObjectException("can‘t deserialize enum"); } }
从代码可以看出，此类不可以实例化。compareTo，是ordinal的比较。一个枚举类型的实现就相当于如下代码:
public class Color extends java.lang.Enum{ public static Color Red = new Color("Red",0); public static Color Green = new Color("Green",1); public static Color Blue = new Color("Blue",2); public Color(String name,int ordinal){ super(name,ordinal); } }
当时编译器并不允许这样显示定义，当时用法是完全是上述定义相符合的
public static void main(String[] args) { System.out.println(Color.class.getSuperclass()); System.out.println(Color.Blue.ordinal()); System.out.println(Color.Blue.name()); }
输出结果:
class java.lang.Enum
2
Blue
如果枚举中包含字段和方法，方法和容易理解，只要是该类型的对象都可以调用该方法，字段和字段的初始化也并不复杂，假如枚举中包含一个int型的value。如上面的Color定义:
public class Color extends java.lang.Enum{ public static Color Red = new Color("Red",0); public static Color Green = new Color("Green",1); public static Color Blue = new Color("Blue",2); public Color(String name,int ordinal){ super(name,ordinal); } public Color(String name,int ordinal,int value){ super(name,ordinal); this.value = value; } public int value; }
除此之外，Color还包含了一些静态方法，valueOf用于根据名称获取该对象，values获取所有该类型的对象示例如下：
public static void main(String[] args) { System.out.println(Color.class.getSuperclass()); for(Color c:Color.values()){ System.out.println(c.name()); } System.out.println(Color.valueOf("Blue")); System.out.println(Enum.valueOf(Color.class,"Blue")); }
输出结果如下:
class java.lang.Enum
Red
Green
Blue
Blue
Blue
标签：nali lan 结果 ack des static java odata 用法
原文地址：http://www.cnblogs.com/yangyang12138/p/7397822.html
