Question

所以我正在尝试做一个测试类，指令是

创建一个名为TestDate的类，其构造函数创建十五个Date对象，并通过调用每个Date的getDayOfTheWeek（）方法显示日期的星期几。日期具体是这些日期，按照这个确切的顺序：

但是当我运行它时，我一直都会遇到错误！我认为这是我的构造函数崩溃或沿着那条线的某个地方。

以下是我的TestDate类代码

public class TestDate
{
private Date date;
/*
 * Main Constructor
 * @param fifteen specific date, test to your heart's content
 */
public TestDate()
{
    Date d1 = new Date(1970, 11, 15); 
    System.out.println(date.getDayOfTheWeek());
    Date d2 = new Date(1887, 7, 31);         
    Date d3 = new Date(1966, 5, 2);          
    Date d4 = new Date(1980, 8, 19);         
    Date d5 = new Date(2001, 9, 11);         
    Date d6 = new Date(1900, 6, 26);         
    Date d7 = new Date(1940, 2, 28);        
    Date d8 = new Date(1974, 10, 30);       
    Date d9 = new Date(1914, 1, 15);        
    Date d10 = new Date(1840, 10, 1);        
    Date d11 = new Date(1999, 12, 31);       
    Date d12 = new Date(1988, 5, 20);       
    Date d13= new Date(2012, 3, 10);         
    Date d14 = new Date(2006, 4, 1);        
    Date d15 = new Date(1992, 2, 29);       


}
}

这是我的Date类构造函数和方法getDayofTheWeek，我认为这是与我的问题相关的所有信息。

public class Date
{
public Date(int year, int month, int day)
{
    setYear(year);
    setMonth(month);
    setDay(day);
}   

public String getDayOfTheWeek()   
{
    int step0 = year%100;
    int step1 = step0 / 12;
    int step2 = step0 % 12;
    int step3 = step2 / 4;
    int step4 = day;    
    int step5 = 0;            
    if(month == JANUARY || month == OCTOBER)
    {
        step5 = JAN_CODE;
    }
    else if(month == FEBURARY || month == MARCH || month == NOVEMBER)
    {
        step5 = FEB_CODE;
    }
    else if(month == APRIL || month == JULY)
    {
        step5 = APR_CODE;
    }
    else if(month == MAY)
    {
        step5 = MAY_CODE;
    }
    else if(month == JUNE)
    {
        step5 = JUN_CODE;
    }
    else if(month == AUGUST)
    {
        step5 = AUG_CODE;
    }
    else if(month == SEPTEMBER || month == DECEMBER)
    {
        step5 = SEP_CODE;
    }
    else
    {
        step5 = 0;
    }  
    if(year/100 ==16 || year/100 == 20)
    {
        step5 = step5 + SPECIAL_CODE_SIX;
    }
    else if(year/100 == 17 || year/100 == 21)
    {
        step5 = step5 + SPECIAL_CODE_FOUR;
    }
    else if(year/100 == 18)
    {
        step5 = step5 + SPECIAL_CODE_TWO;
    }
    int step6 = (step1 + step2 + step3 +step4 + step5)%MOD_CODE;     
    if(step6 == SAT_CODE)
    {
        return "Saturday";
    }
    else if(step6 == SUN_CODE)
    {
        return "Sunday";
    }
    else if(step6 == MON_CODE)
    {
        return "Monday";
    }
    else if(step6 == TUE_CODE)
    {
        return "Tuesday";
    }
    else if(step6 == WED_CODE)
    {
        return "Wednesday";
    }
    else if(step6 == THU_CODE)
    {
        return "Thursday";
    }
    else if(step6 == FRI_CODE)
    {
        return "Friday";
    }
    else
    {
        return null;
    }
} 
}

我在mutator方法中传递了参数

public void setYear(int year)
    {
    if(year <= CURRENT_YEAR && year >= YEAR_ZERO)
    {
        this.year = year;
    }        
}

    public void setMonth(int month)
{
    if(month <= DECEMBER && month >= JANUARY)
    {
        this.month = month;
    }
}

    public void setDay(int day)
{
    if(month == JANUARY || month == MARCH || month == MAY || month == JULY || month == AUGUST
    || month == OCTOBER || month == DECEMBER)
    {
        if(day <= DAY_THIRTY_ONE && day >= DAY_ONE)
        {
            this.day = day;
        }
        else 
        {
            year = CURRENT_YEAR;
            month = JANUARY;
            day = DAY_ONE;
        }
    }    
    else if(month == APRIL || month == JUNE || month == SEPTEMBER || month == NOVEMBER)
    {
        if(day <= DAY_THIRTY && day >= DAY_ONE)
        {
            this.day = day;
        }
        else
        {
            year = CURRENT_YEAR;
            month = JANUARY;
            day = DAY_ONE;
        }
    }
    else if(month == FEBURARY)
    {
        if((isLeapYear() == true) && day <= DAY_FEB_LEAP && day >= DAY_ONE)
        {
            this.day = day;
        }      
        else if((isLeapYear() == false) && day <= DAY_FEB_NORMAL && day >= DAY_ONE)
        {
            this.day = day;
        }  
        else 
        {
            year = CURRENT_YEAR;
            month = JANUARY;
            day = DAY_ONE;
        }
    }        
}
Sorry for the long list of code, I don't really know which ones are useless.

Answer 1

在构造函数的第二行，您正在调用

System.out.println(date.getDayOfTheWeek());

在变量date上，此时为null，因为它尚未初始化。这导致NullPointerException。请阅读此处以获取更多信息：What is a NullPointerException, and how do I fix it?

我（假设）你想做的是：

System.out.println(d1.getDayOfTheWeek());

除此之外的事情我注意到了：

在没有参数的情况下，您可以在javadoc注释中使用@param字段。不要这样做。如果你的构造函数没有参数，那么就不应该有@param。
您正在构造函数中创建15个Date实例，其范围在构造函数完成后立即结束。你可以删除它们，什么都不会改变。我假设你希望这堂课成为一个＆＃34;考试＆＃34;您的日期是否已正确初始化。我建议用main方法（在编码时进行快速测试）和实际的测试框架（如JUnit）来实现这一目标，以便实现＆＃39;测试。如果您有兴趣，可以阅读this教程。它还详细说明了您实际想要测试的原因。

为什么我的测试类不能运行？

1 个答案: