Question

这是我的计算机科学课家庭作业的一部分。我是一名新程序员，并且无法使用检查警报方法。应该检查aHours是否等于小时，aMinutes是否等于分钟，而aSeconds是否等于秒。它一直给我一个错误消息，提示“二进制运算符'=='的错误操作数类型，第一种：int第二种：NumberDisplay”

代码如下：

/**
 * The ClockDisplay class implements a digital clock display for a
 * European-style 24 hour clock. The clock shows hours and minutes. The 
 * range of the clock is 00:00 (midnight) to 23:59 (one minute before 
 * midnight).
 * 
 * The clock display receives "ticks" (via the timeTick method) every minute
 * and reacts by incrementing the display. This is done in the usual clock
 * fashion: the hour increments when the minutes roll over to zero.
 * 
 * @author Michael Kölling and David J. Barnes
 * @version 2016.02.29
 */
public class ClockDisplay
{
    private NumberDisplay hours;
    private NumberDisplay minutes;
    private NumberDisplay seconds;
    private String displayString;    // simulates the actual display
    private int aHours;
    private int aMinutes;
    private int aSeconds;
    private boolean isSet;

    /**
     * Constructor for ClockDisplay objects. This constructor 
     * creates a new clock set at 00:00.
     */
    public ClockDisplay()
    {
        hours = new NumberDisplay(24);
        minutes = new NumberDisplay(60);
        seconds = new NumberDisplay(60);
        updateDisplay();
    }

    /**
     * Constructor for ClockDisplay objects. This constructor
     * creates a new clock set at the time specified by the 
     * parameters.
     */
    public ClockDisplay(int hour, int minute, int second)
    {
        hours = new NumberDisplay(24);
        minutes = new NumberDisplay(60);
        seconds = new NumberDisplay(60);
        setTime(hour, minute, second);
    }

    /**
     * This method should get called once every minute - it makes
     * the clock display go one minute forward.
     */
    public void timeTick()
    {
        minutes.increment();
        if(minutes.getValue() == 0) {  // it just rolled over!
            hours.increment();
        }
        updateDisplay();
    }

    /**
     * Set the time of the display to the specified hour and
     * minute.
     */
    public void setTime(int hour, int minute, int second)
    {
        hours.setValue(hour);
        minutes.setValue(minute);
        seconds.setValue(second);
        updateDisplay();
    }

    /**
     * Return the current time of this display in the format HH:MM.
     */
    public String getTime()
    {
        return displayString;
    }

    /**
     * Update the internal string that represents the display.
     */
    private void updateDisplay()
    {
        displayString = hours.getDisplayValue() + ":" + 
        minutes.getDisplayValue();
    }

    /**
     * Set alarm for clock
     */
    private void setAlarm(int phour, int pminute, int psecond)
    {
        aHours = phour;
        aMinutes = pminute;
        aSeconds = psecond;
        isSet = true;
        System.out.println("Alarm is set");
    }

    /**
     * Cancel alarm for clock
     */
    private void cancelAlarm()
    {
        isSet = false;
        System.out.println("Alarm is off");
    }

    /**
     * Check alarm for clock
     */
    private void checkAlarm()
    {
        if(aHours == hours && aMinutes == minutes && aSeconds == seconds)
        {
            System.out.println("Alarm is off");
            return true;
        }
        else
        {
            return false;
        }
    }
}

这是错误所在：

if(aHours == hours && aMinutes == minutes && aSeconds == seconds)
        {
            System.out.println("Alarm is off");
            return true;
        }
        else
        {
            return false;
        }

Answer 1

在您的代码中，您拥有：

private NumberDisplay hours; // a variable called "hours" that is of type NumberDisplay
private NumberDisplay minutes; // a variable called "minutes" that is of type NumberDisplay
private NumberDisplay seconds; // a variable called "seconds" that is of type NumberDisplay
private int aHours; // a variable called "aHours" that is of type int
private int aMinutes; // a variable called "aMinutes" that is of type int
private int aSeconds; // a variable called "aSeconds" that is of type int

要使aHours == hours && aMinutes == minutes && aSeconds == seconds工作，“小时数”必须是int或不可装箱到int，例如Integer。分钟和秒都一样。

您想要获得的是由以下每种存储的int值：

如果（aHours == hours.getValue（）&& aMinutes == minutes.getValue（）&& aSeconds == seconds.getValue（））{

如您在

中所见

public void timeTick()
{
    minutes.increment();
    if(minutes.getValue() == 0) {  // it just rolled over!
        hours.increment();
    }
    updateDisplay();
}

方法minutes有一个.getValue()方法可返回int。

Answer 2

您发布的代码几乎没有问题。

但是，要回答您的问题，您会收到错误消息，因为您试图将int与NumberDisplay进行比较以查看它们是否相等。

在Java中，您不能这样做。相反，您需要执行以下操作之一：

a）将int转换为NumberDisplay，然后使用NumberDisplay.equals（）比较它们（但您可能必须自己编写该方法-尝试研究“在Java中重写等于”）

b）将NumberDisplay转换为int，然后使用当前使用的==运算符进行比较。转换为int的方式取决于NumberDisplay代码的作用。

c）写一个知道如何比较NumberDisplay和int的方法，并使用它。确切的工作方式取决于NumberDisplay的代码，但是通常您会在NumberDisplay中创建一个带有如下签名的方法：

public boolean isTheSame(int compare)

正如注释中所指出的那样，您还需要更改代码，以使任何返回true或false的方法都具有boolean而不是{ {1}}

Answer 3

需要更改两件事：函数返回类型应为boolean。您需要获取NumberDisplay元素的值。由于我没有NumberDisplay的代码，因此我假设您可以使用getValue。这给出了以下代码：

    /**
     * Check alarm for clock
     */
    private boolean checkAlarm()
    {
        if(aHours == hours.getValue() && aMinutes == minutes.getValue() && aSeconds == seconds.getValue())
        {
            System.out.println("Alarm is off");
            return true;
        }
        else
        {
            return false;
        }
    }

int不能转换为布尔值？

3 个答案: