java - 如何在静态枚举中获取下一个

Question

public enum Planet { 
    MERCURY(false),
    VENUS(false),
    EARTH(false),
    MARS(false),
    JUPITER(false),
    SATURN(false),
    URANUS(false),
    NEPTUNE(false); 
}

    public boolean isCurrent;

    Planet(boolean isCurrent){
       this.isCurrent = isCurrent;
    }

    public static void next(){
    if(planet == VENUS){
        VENUS.isCurrent = false;
        EARTH.isCurrent = true;
        MARS.isCurrent = false;
        JUPITER.isCurrent = false;
        SATURN.isCurrent = false;
        URANUS.isCurrent = false;
        NEPTUNE.isCurrent = false;
    }
    if(planet == EARTH){
        VENUS.isCurrent = false;
        EARTH.isCurrent = false;
        MARS.isCurrent = true;
        JUPITER.isCurrent = false;
        SATURN.isCurrent = false;
        URANUS.isCurrent = false;
        NEPTUNE.isCurrent = false;
    }
...  
}

我找到了这个解决方案，

private enum Planet { MERCURY, VENUS, EARTH, MARS, JUPITER, SATURN, URANUS, NEPTUNE;
    public Planet getNext() {
        return this.ordinal() < Planet.values().length - 1
            ? Planet.values()[this.ordinal() + 1]
            : null;
    }
}

但我无法使用this，因为这个枚举在其他类中作为静态导入；

现在我使用以下结构:

 public static Planet setNewCurrent(){
    for(Planet planet : Planet.values()){
        if(planet == VENUS){
            VENUS.isCurrent = false;
            EARTH.isCurrent = true;
            MARS.isCurrent = false;
            JUPITER.isCurrent = false;
            SATURN.isCurrent = false;
            URANUS.isCurrent = false;
            NEPTUNE.isCurrent = false;
        }
        if(planet == EARTH){
            VENUS.isCurrent = false;
            EARTH.isCurrent = false;
            MARS.isCurrent = true;
            JUPITER.isCurrent = false;
            SATURN.isCurrent = false;
            URANUS.isCurrent = false;
            NEPTUNE.isCurrent = false;
        }
...
    }
}   

有谁知道像这样获取NextPlanet()的一些方便的方法

planet.getNext().isCurrent = true;

Answer 1

我希望您确实意识到您可以拥有如下内容:

public enum Planet { 
    MERCURY, VENUS, EARTH, MARS, JUPITER, SATURN, URANUS, NEPTUNE; 

    public Planet getNext() {
        return this.ordinal() < Planet.values().length - 1
            ? Planet.values()[this.ordinal() + 1]
            : null;
    }
}

private Planet planet;

public void someFunction()
{
    planet = Planet.MARS;
    planet = planet.getNext();
    if(planet != null)
    {
        doStuff();
    }
}

当然，您可以根据在字段变量中选择的任何一个，将 switch-case 语句与枚举一起使用:Java using enum with switch statement

根本不需要一个 boolean 变量来确定哪个是“当前选中的”。

编辑:根据您的评论，您需要 Planet 的单例实例。幸运的是，您可以为此使用枚举本身:

public enum Planet { 
    MERCURY, VENUS, EARTH, MARS, JUPITER, SATURN, URANUS, NEPTUNE; 

    private static Planet currentPlanet = MERCURY;

    public static Planet getCurrentPlanet()
    {
        return currentPlanet;
    }

    public static boolean setToNext() {
        boolean retVal = this.ordinal() < Planet.values().length - 1;
        currentPlanet = this.ordinal() < Planet.values().length - 1
                ? Planet.values()[this.ordinal() + 1]
                : Planet.values()[0];
        return retVal; //returns false when it was the last element of the enum
    }
}


public void doSomething()
{
    Planet planet;
    do
    {
        planet = Planet.getCurrentPlanet();
        //do things with planet, like write out their names
        System.out.println(planet.name());
    }
    while(Planet.setToNext());
}