枚举
enum 是 Java 5 开始支持的关键字,它带来了一个新的数据类型:枚举型。Java 中的枚举型数据——与我最初设想的不同——并非具名的整型数值,而是货真价实的对象。除了开头的数值枚举部分,枚举型的声明过程与类定义无异,而事实上,所有的枚举型也确实是 java.lang.Enum 的子类。
DEMO
简单的枚举型示例:
public enum Day {
SUNDAY, MONDAY, TUESDAY, WEDNESDAY,
THURSDAY, FRIDAY, SATURDAY
}
// @cite http://docs.oracle.com/javase/tutorial/java/javaOO/enum.html
较复杂的枚举型示例:
public enum Planet {
MERCURY (3.303e+23, 2.4397e6),
VENUS (4.869e+24, 6.0518e6),
EARTH (5.976e+24, 6.37814e6),
MARS (6.421e+23, 3.3972e6),
JUPITER (1.9e+27, 7.1492e7),
SATURN (5.688e+26, 6.0268e7),
URANUS (8.686e+25, 2.5559e7),
NEPTUNE (1.024e+26, 2.4746e7);
private final double mass; // in kilograms
private final double radius; // in meters
Planet(double mass, double radius) {
this.mass = mass;
this.radius = radius;
}
private double mass() { return mass; }
private double radius() { return radius; }
// universal gravitational constant (m3 kg-1 s-2)
public static final double G = 6.67300E-11;
double surfaceGravity() {
return G * mass / (radius * radius);
}
double surfaceWeight(double otherMass) {
return otherMass * surfaceGravity();
}
}
// @cite http://docs.oracle.com/javase/tutorial/java/javaOO/enum.html
enum vs. Enumeration
enum 是一个数据类型,本质上是一个类;而 Enumeration 是一个接口。
REF
- The Java™ Tutorials: Enum Types
http://docs.oracle.com/javase/tutorial/java/javaOO/enum.html