Java学习，枚举

Java 中枚举（enum）是一种特殊的类，用于表示一组固定的常量。枚举类型使得代码更加清晰、类型安全，并且易于维护。

基本用法：
定义枚举：
public enum Day {
    MONDAY,
    TUESDAY,
    WEDNESDAY,
    THURSDAY,
    FRIDAY,
    SATURDAY,
    SUNDAY
}

示例：

public class EnumExample {
    public static void main(String[] args) {
        Day today = Day.WEDNESDAY;
 
        switch (today) {
            case MONDAY:
                System.out.println("Today is Monday.");
                break;
            case WEDNESDAY:
                System.out.println("Today is Wednesday.");
                break;
            // 其他 case 语句
            default:
                System.out.println("Today is another day.");
                break;
        }
    }
 

枚举中方法和构造函数
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);
 
    private final double mass;   // in kilograms
    private final double radius; // in meters
 
    // 构造函数
    Planet(double mass, double radius) {
        this.mass = mass;
        this.radius = radius;
    }
 
    public double mass() { return mass; }
 
    public double radius() { return radius; }
 
    // 示例方法：计算表面重力
    public double surfaceGravity() {
        final double G = 6.67300E-11;
        return G * mass / (radius * radius);
    }
 
    public static void main(String[] args) {
        double earthGravity = EARTH.surfaceGravity();
        System.out.println("Earth's surface gravity is " + earthGravity + " m/s^2");
    }
}

枚举的迭代
enum Color
{
    RED, GREEN, BLUE;
}
public class MyClass {
  public static void main(String[] args) {
    for (Color myVar : Color.values()) {
      System.out.println(myVar);
    }
  }
}