java - void在java中有什么作用？

Question

The return type—the data type of the value returned by the method, or void if the method does not return a value.

http://download.oracle.com/javase/tutorial/java/javaOO/methods.html

好的，那么..这是我的问题:

public class EnumTest {
    Day day;

    public EnumTest(Day day) {
        this.day = day;
    }

    public void tellItLikeItIs() {
        switch (day) {
            case MONDAY: System.out.println("Mondays are bad.");
                         break;

            case FRIDAY: System.out.println("Fridays are better.");
                         break;

            case SATURDAY:
            case SUNDAY: System.out.println("Weekends are best.");
                         break;

            default:     System.out.println("Midweek days are so-so.");
                         break;
        }
    }

    public static void main(String[] args) {
        EnumTest firstDay = new EnumTest(Day.MONDAY);
        firstDay.tellItLikeItIs();
        EnumTest thirdDay = new EnumTest(Day.WEDNESDAY);
        thirdDay.tellItLikeItIs();
        EnumTest fifthDay = new EnumTest(Day.FRIDAY);
        fifthDay.tellItLikeItIs();
        EnumTest sixthDay = new EnumTest(Day.SATURDAY);
        sixthDay.tellItLikeItIs();
        EnumTest seventhDay = new EnumTest(Day.SUNDAY);
        seventhDay.tellItLikeItIs();


    }
}

http://download.oracle.com/javase/tutorial/java/javaOO/enum.html

如果没有 void，上面的代码将无法工作。

Exception in thread "main" java.lang.Error: Unresolved compilation problems: 
    The method tellItLikeItIs() is undefined for the type EnumTest

我错过了什么？为什么里面会有空隙？它确实返回一个字符串？

Answer 1

你是说 tellItLikeItIs 方法？是的，您必须指定 void 以指定方法不返回任何内容。所有方法必须指定返回类型，即使它是void。

它肯定不会返回字符串 - 看，任何地方都没有 return 语句。不太清楚为什么您认为它 返回的是字符串。它向控制台打印字符串，但这与从该方法返回字符串不同。