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An enum type is a special data type.
It enables for a variable to be a set of predefined constants. Because they are constants, the names of an enum type‘s fields are in UPPERCASE letters.
For example, you can specify a days-of-the-week enum type as:
public enum Day { SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY }
You can use enum by . (dot), example Day.MONDAY
Enum can be more powerful. The enum declaration defines a class (called an enum type). The enum class body can include methods and other fields.
For example, you can specify a planet enum type:
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) { if (args.length != 1) { System.err.println("Usage: java Planet <earth_weight>"); System.exit(-1); } double earthWeight = Double.parseDouble(args[0]); double mass = earthWeight/EARTH.surfaceGravity(); for (Planet p : Planet.values()) System.out.printf("Your weight on %s is %f%n", p, p.surfaceWeight(mass)); } }
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原文地址：http://www.cnblogs.com/ireneyanglan/p/4950005.html
