[OCPJP]enum的用法

Given:

public enum USCurrency {
    PENNY(1),
    NICKLE(5),
    DIME(10),
    QUARTER(25);
    private int value;

    public USCurrency(int value) {
        this.value = value;
    }

    public int getValue() {
        return value;
    }
}

public class Coin {

    public static void main(String[] args) {
        USCurrency usCoin = new USCurrency.DIME;
        System.out.println(usCoin.getValue());
    }
}

Which two modifications enable the given code to compile?

A. Nest the USCurrency enumeration declaration within the Coin class.
B. Make the USCurrency enumeration constructor private.
C. Remove the new keyword from the instantion of usCoin.
D. Make the getter method of value as a static method.
E. Add the final keyword in the declaration of value.

題解

enum建構子的可見度只能使用default或是private。使用enum預先列舉好的常數不需要使用new運算子。因此這題答案是選項B和選項C。