检查Enum是空还是空

Question

我正在尝试验证正在发送到我的控制器的json,并且我正在使用BindingResult方式,我能够正常验证字符串和其他所有内容.但我不知道如何检查枚举是空还是空.

Answer 1

您可以简单地使用：Objects.isNull(enumValue)

Answer 2

首先,Enum不能为空!它是表示已定义状态的Object.可以把它想象成一个静态的最终对象,它在初始化后无法改变,但很容易进行比较.

所以你可以做的是检查null和Equals到你现有的枚举值.

根据要求,这里有关于Enum比较的基础知识:

public enum Currency {PENNY, NICKLE, DIME, QUARTER};

Currency coin = Currency.PENNY;
Currency noCoin = null
Currency pennyCoin = Currency.PENNY;
Currency otherCoin = Currency.NICKLE;

if (coin != null) {
    System.out.println("The coin is not null");
}

if (noCoin == null) {
    System.out.println("noCoin is null");
}

if (coin.equals(pennyCoin)) {
    System.out.println("The coin is a penny, because its equals pennyCoin");
}

if (coin.equals(Currency.PENNY)) {
    System.out.println("The coin is a penny, because its equals Currency.PENNY");
}

if (!coin.equals(otherCoin)) {
    System.out.println("The coin is not an otherCoin");
}

switch (coin) {
    case PENNY:
        System.out.println("It's a penny");
        break;
    case NICKLE:
        System.out.println("It's a nickle");
        break;
    case DIME:
        System.out.println("It's a dime");
        break;
    case QUARTER:
        System.out.println("It's a quarter");
        break;
}

Output: "It's a penny"