java的enum其实是一个类。编译器根据你enum的定义会为你生成一个 java.lang.Enum<E>的子类。java.lang.Enum<E>是一个抽象类，定义了很多final方法，也就是说你定义的enum类里不能覆盖它们，你唯一能覆盖的是Object.toString类。同时你定义的enum类是不能被继承的。
先来看看java.lang.Enum类的代码
注意，更具
编码规范，
枚举值应该全大写（按照常量编写规范）
/*
* %W% %E%
*
* Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
*
ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.lang;
import java.io.Serializable;
import java.io.IOException;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.ObjectStreamException;
/**
* This is the common base
class of all Java language enumeration types.
*
* @author Josh Bloch
* @author Neal Gafter
* @version %I%, %G%
* @since 1.5
*/
public abstract class Enum<E extends Enum<E>>
implements Comparable<E>, Serializable {
/**
* The name of this enum constant, as declared in the enum declaration.
* Most programmers should use the {@link #toString} method rather than
* accessing this field.
*/
private final String name;
/**
* Returns the name of this enum constant, exactly as declared in its
* enum declaration.
*
* <b>Most programmers should use the {@link #toString} method in
* preference to this one, as the toString method may return
* a more user-friendly name.</b> This method is designed primarily for
* use in specialized situations where correctness depends on getting the
* exact name, which will not vary from release to release.
*
* @return the name of this enum constant
*/
public final String name() {
return name;
}
/**
* The ordinal of this enumeration constant (its position
* in the enum declaration, where the initial constant is assigned
* an ordinal of zero).
*
* Most programmers will have no use for this field. It is designed
* for use by sophisticated enum-based data structures, such as
* {@link java.util.EnumSet} and {@link java.util.EnumMap}.
*/
private final int ordinal;
/**
* Returns the ordinal of this enumeration constant (its position
* in its enum declaration, where the initial constant is assigned
* an ordinal of zero).
*
* Most programmers will have no use for this method. It is
* designed for use by sophisticated enum-based data structures, such
* as {@link java.util.EnumSet} and {@link java.util.EnumMap}.
*
* @return the ordinal of this enumeration constant
*/
public final int ordinal() {
return ordinal;
}
/**
* Sole constructor. Programmers
cannot invoke this constructor.
* It is for use by code emitted by the compiler in response to
* enum type declarations.
*
* @param name - The name of this enum constant, which is the identifier
* used to declare it.
* @param ordinal - The ordinal of this enumeration constant (its position
* in the enum declaration, where the initial constant is assigned
* an ordinal of zero).
*/
protected Enum(String name, int ordinal) {
this.name = name;
this.ordinal = ordinal;
}
/**
* Returns the name of this enum constant, as contained in the
* declaration. This method may be overridden, though it typically
* isn't necessary or desirable. An enum type should override this
* method when a more "programmer-friendly" string form exists.
*
* @return the name of this enum constant
*/
public String toString() {
return name;
}
/**
* Returns true if the specified object is equal to this
* enum constant.
*
* @param other the object to be compared for equality with this object.
* @return true if the specified object is equal to this
* enum constant.
*/
public final boolean equals(Object other) {
return this==other;
}
/**
* Returns a
hash code for this enum constant.
*
* @return a hash code for this enum constant.
*/
public final int hashCode() {
return super.hashCode();
}
/**
* Throws CloneNotSupportedException. This guarantees that enums
* are never cloned, which is necessary to preserve their "singleton"
* status.
*
* @return (never returns)
*/
protected final Object clone() throws CloneNotSupportedException {
throw new CloneNotSupportedException();
}
/**
* Compares this enum with the specified object for order. Returns a
* negative integer, zero, or a positive integer as this object is less
* than, equal to, or greater than the specified object.
*
* Enum constants are only comparable to other enum constants of the
* same enum type. The natural order implemented by this
* method is the order in which the constants are declared.
*/
public final int compareTo(E o) {
Enum other = (Enum)o;
Enum self = this;
if (self.getClass() != other.getClass() && // optimization
self.getDeclaringClass() != other.getDeclaringClass())
throw new ClassCastException();
return self.ordinal - other.ordinal;
}
/**
* Returns the Class object corresponding to this enum constant's
* enum type. Two enum constants e1 and e2 are of the
* same enum type if and only if
* e1.getDeclaringClass() == e2.getDeclaringClass().
* (The value returned by this method may differ from the one returned
* by the {@link Object#getClass} method for enum constants with
* constant-specific class bodies.)
*
* @return the Class object corresponding to this enum constant's
* enum type
*/
public final Class<E> getDeclaringClass() {
Class clazz = getClass();
Class zuper = clazz.getSuperclass();
return (zuper == Enum.class) ? clazz : zuper;
}
/**
* Returns the enum constant of the specified enum type with the
* specified name. The name must match exactly an identifier used
* to declare an enum constant in this type. (Extraneous whitespace
* characters are not permitted.)
*
* @param enumType the <tt>Class</tt> object of the enum type from which
* to return a constant
* @param name the name of the constant to return
* @return the enum constant of the specified enum type with the
* specified name
* @throws IllegalArgumentException if the specified enum type has
* no constant with the specified name, or the specified
* class object does not represent an enum type
* @throws
NullPointerException if <tt>enumType</tt> or <tt>name</tt>
* is null
* @since 1.5
*/
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 const " + enumType +"." + name);
}
/**
* prevent default deserialization
*/
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");
}
/**
* enum classes cannot have finalize methods.
*/
protected final void finalize() { }
}
如上所示，它本身提供了很多方法。
当然我们写的enum，将会直接从上面的父类继承下这些方法来。
例1
package test;
public enum Enum1 {
ONE, TWO, THREE
}
package test;
public class TestEnum1 {
/**
* 描述:
* @param args
* @author liyixing 2013-12-13 下午4:52:01
*/
public static void main(String[] args) {
for (Enum1 n: Enum1.values()) {
System.out.println("ordinal: " + n.ordinal()); // enum's int value, start from 0 by default
System.out.println(n.compareTo(Enum1.TWO));
System.out.println(n == Enum1.THREE);
System.out.println(n.name());
System.out.println(n.getDeclaringClass()); // Number
}
}
}
在使用枚举时，必须用类型名作前缀，比如Number.ONE，而不能直接用ONE。如果
你需要这种便利的话，可以用import static Number.*;来达到目的。
如
import static test.Enum1.ONE;
System.out.println(Enum1.ONE == ONE); //
另外使用在switch语句中
switch (n) {
case ONE:
break;
case TWO:
break;
default:
break;
}
这里如果写case Enum1.ONE是不允许的。
我们可以往enum里添加属性和方法，
构造函数：
需要注意的是，构造函数只能使用private或者不写（默认是private)修饰符
package test;
public enum Enum1 {
ONE, TWO, THREE;
private String name;
public Integer id;
// 默认构造
private Enum1() {
}
// 带参数构造
Enum1(String name) {
}
private void print() {
System.out.println(name);
}
public String say() {
print();
return name;
}
}
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