java - 如何正确地为变量分配 boolean 值并对其进行测试？

Question

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What does a "Cannot find symbol" or "Cannot resolve symbol" error mean? (18 个回答)

已关闭 5 年前。

我正在尝试创建一个类，使用三个整数变量来设置时间，分别表示小时、分钟和秒数，以及第四个 boolean 变量来设置 AM 或 PM。我能够使三个整数变量正常工作，但我不知道我在 boolean 变量未正确分配或测试方面做错了什么。

public class Time
{
    private int hour;
    private int minute;
    private int second;
    private boolean amPm;

    public Time(int setHour, int setMinute, int setSecond, boolean setAmPm)
    {
        hour = setHour;
        minute = setMinute;
        second = setSecond;
        amPm = setAmPm;
    }

    public String toString()
    {
        if (amPm == true)
        {
            String halfDay = "P.M.";
        }
        else
        {
            String halfDay = "A.M.";
        }
        return hour + ":" + minute + ":" + second + " " + halfDay + ".";
    }
}

Answer 1

您不能使用 halfDay，因为它超出了范围

In computer programming, the scope of a name binding – an association of a name to an entity, such as a variable – is the region of a computer program where the binding is valid: where the name can be used to refer to the entity. Such a region is referred to as a scope block. In other parts of the program the name may refer to a different entity (it may have a different binding), or to nothing at all (it may be unbound).

在其他世界中，您在 if/else 语句中声明 halfDay，但一旦您关闭括号，它就会消失。如果您想将它用于串联，则需要通过之前声明来更改他的范围。

public class Time
{
    private int hour;
    private int minute;
    private int second;
    private boolean amPm;

    public Time(int setHour, int setMinute, int setSecond, boolean setAmPm)
    {
        hour = setHour;
        minute = setMinute;
        second = setSecond;
        amPm = setAmPm;
    }

    public String toString()
    {
        String halfDay;
        if (amPm == true)
        {
            halfDay = "P.M.";
        }
        else
        {
            halfDay = "A.M.";
        }
        return hour + ":" + minute + ":" + second + " " + halfDay + ".";
    }
}