java - 具有抽象函数的 Java 枚举有哪些非抽象版本不能做的事情？ (即是否存在技术差异，或者只是一种模式？)-6ren

java - 具有抽象函数的 Java 枚举有哪些非抽象版本不能做的事情？ (即是否存在技术差异，或者只是一种模式？)

转载作者：行者123 更新时间：2023-11-29 06:51:53

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好的，在this answer在堆栈上，答案的海报显示了一个示例，说明如何在枚举中使用抽象方法。我会在这里为后代重复这个答案，尽管稍作修改以更好地说明我的问题的基础。

考虑这个使用抽象方法的枚举:

public enum Vehicle {
    CAR {
        public String action() { return "DRIVE!"; }
    },
    TRUCK {
        public String action() { return "DRIVE!"; }
    },
    BUS {
        public String action() { return "DRIVE!"; }
    },
    TRACTOR {
        public String action() { return "DRIVE!"; }
    },
    MOTORCYCLE {
        public String action() { return "RIDE!"; }
    },
    BOAT {
        public String action() { return "SAIL!"; }
    },
    AIRPLANE {
        public String action() { return "PILOT!"; }
    };

    public abstract String action();
}

如您所见，由于“action”是一个抽象函数，因此每个元素都必须通过枚举的匿名子类定义覆盖。

将此与这个无抽象、功能相同的版本进行对比，后者甚至使用完全相同的 API:

enum Vehicle {
    CAR,
    TRUCK,
    BUS,
    TRACTOR,
    MOTORCYCLE,
    BOAT,
    AIRPLANE;

    public String action(){
        switch(this)
        {
            case MOTORCYCLE : return "RIDE!";
            case BOAT       : return "SAIL!";
            case AIRPLANE   : return "FLY!";
            default         : return "DRIVE!";
        }
    }
}

在此示例中，您只需指定与默认值不同的特定情况。此外，它将值保存在一个漂亮、干净、可读的列表中，并减少了大量无关代码。

也许我遗漏了什么，但是抽象方法方法有技术优势吗？它究竟给了你什么非抽象版本没有的？它有任何额外的功能吗？

Note: I suspect the actual answer is because it's not really a function of an enum per se, but rather it's because the enum is compiled to a class and a class supports abstract functions.

However, I'm not exactly sure that's correct either because as others have shown, an enum compiles down to a static final class which means it can't be subclassed. Perhaps the compiler doesn't add the 'final' when using abstract functions. Not sure as I haven't been able to view generated output so I can't say for sure, but that would make sense.

But specifically for this question, is there anything an enum with an abstract function can do that a non-abstract version can't?