如何自定义 enum类型

package com.jin.enums;

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),
    PLUTO   (1.27e+22,  1.137e6);

    private final double mass;   // in kilograms
    private final double radius; // in meters
    Planet(double mass, double radius) {
        this.mass = mass;
        this.radius = radius;
    }
    public double mass()   { return mass; }
    public double radius() { return radius; }

    // universal gravitational constant  (m3 kg-1 s-2)
    public static final double G = 6.67300E-11;

    public double surfaceGravity() {
        return G * mass / (radius * radius);
    }
    public double surfaceWeight(double otherMass) {
        return otherMass * surfaceGravity();
    }
}

 形式二

package com.jin.enums;

public enum Operation {
//	PLUS, MINUS, TIMES, DIVIDE;
//
//    // Do arithmetic op represented by this constant
//    double eval(double x, double y){
//        switch(this) {
//            case PLUS:
//            {
//            	System.out.println("aa");
//            	System.out.println("aa");
//            	System.out.println("aa");
//            	return x + y;
//            }
//            case MINUS:  return x - y;
//            case TIMES:  return x * y;
//            case DIVIDE: return x / y;
//        }
//        throw new AssertionError("Unknown op: " + this);
//    }
	
	PLUS   { double eval(double x, double y) { return x + y; } },
	MINUS  { double eval(double x, double y) { return x - y; } },
	TIMES  { double eval(double x, double y) { return x * y; } },
	DIVIDE { double eval(double x, double y) { return x / y; } };

	// Do arithmetic op represented by this constant
	abstract double eval(double x, double y);
}

 形式三：

package com.jin.enums;

public enum Color {
	RED, GREEN, YELLOW, BLUCK
}

 

 使用：

package com.jin.enums;

public class Test {
	public static void main(String[] args) {
//		System.out.println(Color.valueOf("RED"));
//		System.out.println(Planet.VENUS.radius());
		System.out.println(Operation.PLUS.eval(1, 3));
	}
}