声明后填充数组成员

Question

My class has an array as one of it's members. Inside the constructor, I want to populate it's members to the following. How can I do that, it gives me an error.

public class GetCurrentMonth {

    Calendar now;
    String[] monthNames;

    /**
     * 
     */
    public GetCurrentMonth() {
        now = Calendar.getInstance();
        monthNames = {"January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};
    }

    public String getMonth()
    {
        return monthNames[(now.get(Calendar.MONTH) + 1)];
    }
}

I do not want to add these month names at the constructor as follows, since I want to follow good coding practice, and I was told that all initializations should be done inside the constructor.

String[] monthNames = {"January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};

Answer 1

Firstly, not only is it not good practice to initialize in the constructor, it's actually bad practice, because:

• you actually have to code a constructor (adding useless code)
• fields should be static final if they're the same for every instance, like the months
• instance fields should final where possible and be initialised on declaration if there's only one way to initialize them

Best practice, including adhering to naming standards, says your class should look like this:

public class GetCurrentMonth {
    private static final String[] MONTH_NAMES = {"January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};
    private final Calendar now = Calendar.getInstance();

    public String getMonth() {
        return MONTH_NAMES [(now.get(Calendar.MONTH) + 1)];
    }
}

Answer 2

您需要使用新的String []创建数组

monthNames = new String[] {"January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};

Answer 3

First, I agree with the answer from Bohemian♦, But I even would go further and recommend that you create an Enum that holds your month names. Here is how I would do it:

public enum Month {
    JANUARY("January"), 
    FEBRUARY("February"), 
    MARCH("March"), 
    APRIL("April"), 
    MAY("May"),
    JUNE("June"), 
    JYLY("July"), 
    AUGUST("August"), 
    SEPTEMBER("September"),
    OCTOBER("October"), 
    NOVEMBER("November"), 
    DECEMBER("December");

    private String displayName;

    private Month(String displayName) {
        this.displayName = displayName;
    }

    @Override
    public String toString() {
        return displayName;
    }

    public static Month valueOfIgnoreCase(String value) {
        return valueOf(value.toUpperCase());
    }
}