How to handle exceptions when Java enum values are thrown?

1 year ago
Sophia Anderson
2 minutes

When the values() method is used to obtain enumeration instances, if no instances are defined in the enumeration class, this method will throw a NullPointerException. To resolve this issue, you can add a conditional statement in the enumeration class to avoid throwing an exception.

For instance, suppose there is an enumeration class called MyEnum that can solve this issue in the following manner.

public enum MyEnum {
    VALUE1,
    VALUE2,
    VALUE3;

    public static MyEnum[] values() {
        MyEnum[] values = MyEnum.values();
        if (values.length == 0) {
            throw new IllegalStateException("No instances defined for this enum");
        }
        return values;
    }
}

In the above code, the values() method was overridden and a check was added inside the method. If the number of enum instances is 0, an IllegalStateException will be thrown. This way, calling the values() method will not result in a NullPointerException.

Alternatively, you can store enum instances in a static member variable within the enum class to prevent recalculating the enum instances every time the values() method is called. For example:

public enum MyEnum {
    VALUE1,
    VALUE2,
    VALUE3;

    private static final MyEnum[] VALUES = MyEnum.values();

    public static MyEnum[] values() {
        if (VALUES.length == 0) {
            throw new IllegalStateException("No instances defined for this enum");
        }
        return VALUES;
    }
}

In the above code, enumerations instances are stored in a static member variable named VALUES, and directly returned using this variable in the values() method. Additionally, by calling the values() method, no NullPointerException exception will be thrown.

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