JAVA中的枚举类型

// Enum type with data and behavior - Pages 149-150
package test.package30;

public enum Planet {
MERCURY(3.302e+23, 2.439e6),
VENUS(4.869e+24, 6.052e6),
EARTH(5.975e+24, 6.378e6),
MARS(6.419e+23, 3.393e6),
JUPITER(1.899e+27, 7.149e7),
SATURN(5.685e+26, 6.027e7),
URANUS(8.683e+25, 2.556e7),
NEPTUNE(1.024e+26, 2.477e7);
private final double mass; // 质量
private final double radius; // 半径
private final double surfaceGravity; // 表面重力

// 万有引力常数
private static final double G = 6.67300E-11;

// 构造函数
Planet(double mass, double radius) {
this.mass = mass;
this.radius = radius;
surfaceGravity = G * mass / (radius * radius);
}

//得到质量
public double mass() {
return mass;
}

//得到半径
public double radius() {
return radius;
}

//得到表面重力
public double surfaceGravity() {
return surfaceGravity;
}

//牛顿定律 F=ma
public double surfaceWeight(double mass) {
return mass * surfaceGravity; // F = ma
}
}