java enum用法基本用法
enum Day { SUNDAY, MONDAY, TUESDAY, WENDSDAY, THURSDAY, FRIDAY, SATURDAY;}
枚举是常量，所以应该用大写。
枚举是对象
枚举隐含地继承了java.lang.Enum，所以它具有java.lang.Enum的属性和方法。遍历枚举：
public class Main { public static void main(String[] args) { for(Day day:Day.values()) { System.out.PRintln(day); } }}
枚举可以带字段和方法，以下示例来自官方The Java? Tutorials
public enum EnumDemo { AOBJECT("field one", "field two"); private String field1; private String field2; EnumDemo(String val1, String val2){ this.field1 = val1; this.field2 = val2; } public void printFields(){ System.out.println(this.field1); System.out.println(this.field2); } public static void main(String[] args) { EnumDemo.AOBJECT.printFields(); }}
以下现实中的示例来自官方的Java Tutorial:
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(); } public static void main(String[] args) { Double earthWeight = 120; for(Planet p: Planet.values()){ System.out.println(p.surfaceGravity()); System.out.println(p.surfaceWeight(earthWeight/EARTH.surfaceGravity())); } }}
枚举是singleton，可以用枚举来构建一个Singleton
public enum Singleton { INSTANCE(new String[]{"arg1", "arg2"}); String[] myArgs; Singleton(String[] args){ this.myArgs = args; } public static Singleton getInstance(){ return INSTANCE; } public static void main(String[] args) { for(String arg : INSTANCE.myArgs) System.out.println(arg); }}