Question

我创建了一个名为2d的对象数组，它存储了一个String国家和一个double数组。我在实施某个功能以检索某个国家/地区的手机统计信息总数时遇到了问题。基本上如果年份小于1983年（自1983年数据开始的起始年份），它应该返回-1，因为它超出界限。尝试实现的函数称为

getNumSubscriptionsInCountryForPeriod(String country, int startYear, int endYear)

您打算打印统计数据，年初和年末的国家/地区。然后通过获取年份的索引差异来添加所选时间段的总和，但我无法实现它。因此，例如，如果我通过（＆＃34; USA＆＃34;，1983,1989），它应该打印1983年和1989年之间的统计总数。显示应该是：usa（1983年至1989年）：3.14。我在尝试访问对象中的值时遇到了麻烦，无法转换/转换为对象。请建议会有所帮助。

public class CellularData {

private Object [][]array;

public CellularData(int rows, int columns, int year)
{
    array = new Object[rows+1][columns+1];
    array[0][0] = "Country";
    this.year = year;
    for(int i=1;i<=columns;i++)
    {
    array[0][i] = year++;
    }
}

public void addCountry(String country, double []num)
{
    for(int i=0;i<array.length;i++)
    {    
    if(array[i][0] == null)
    {
        addCountry(country, num, i);
        break;
    }
    }
}
private void addCountry(String country, double []num, int row)
{
    array[row][0] = country;
    for(int j = 1;j<array[row].length;j++)
    {
        array[row][j] = num[j-1];
    }
}
public double getNumSubscriptionsInCountryForPeriod(String country, int sYear, int eYear)
{//trouble implementing the function
    double sum = 0;
    int indexStart = (int)(sYear - ((Integer) array[0][1]).doubleValue());

    for(int i=1;i<array.length;i++)
    {
        if(array[i][0]==country && ((sYear<year)||(eYear>year)))
        {
            //System.out.print(array[i][0]);

        }
    }
    return sum;
}

public String toString()
{
    for(Object []a: array)
    {
        for(Object k:a)
        {
            System.out.print(k + "\t");
        }
        System.out.println();
    }
    return " ";
}
}

 public class TestCellularData {

public static void main(String []args)
{
    final double[] usaPartial = {0,0,0.14,.28,.5,.83,1.39};
    final double[] canadaPartial = {0,0,.05,.23,.37,.75,1.26};
    final double[] mexicoPartial = {0,0,0,0,0,0,0.01};

     int numRows = 3;
     int numColumns = canadaPartial.length;
     int startingYear = 1983;

    CellularData datatable = new CellularData(numRows, numColumns, startingYear);
    datatable.addCountry("USA", usaPartial);
    datatable.addCountry("Mexico", mexicoPartial);
    datatable.addCountry("Canada", canadaPartial);

    System.out.println(datatable);

    System.out.printf("usa (1983 to 1989): %.2f \n",     datatable.getNumSubscriptionsInCountryForPeriod("usa",1983,1989));
    // country is "usa", subscriptions from 1983 to 1989
    // the output is: 
    // usa (1983 to 1989): 3.14
    System.out.printf("mexico (1983 to 1989): %.2f \n", datatable.getNumSubscriptionsInCountryForPeriod("mexico",1983,1989));
    // country is "mexico", subscriptions from 1983 to 1986
    // the output is:
    // mexico (1983 to 1989): 0.01                  
    // NOTE: in order to get this result, you must test beyond the sample data included here and refer to the CSV file.
    System.out.printf("canada (1890 to 2000): %.2f \n", datatable.getNumSubscriptionsInCountryForPeriod("canada",1890, 2000));
    // the output is:
    // ERROR : requested year 1890  is less than starting year 1893
    // canada (1890 to 2000): -1.00 
   }

Answer 1

首先，添加您在阵列中拥有的国家/地区数量：

public class CellularData {

    private Object[][] array;
    private final int year;
    private int countryNum = 0;  // number of countries in array

    public CellularData(int rows, int columns, int year) {
        array = new Object[rows + 1][columns + 1];
        array[0][0] = "Country";
        this.year = year;
        for (int i = 1; i <= columns; i++) {
            array[0][i] = year++;
        }
        countryNum = 1;
    }

现在您可以将addCountry方法更改为：

public void addCountry(String country, double[] num) {
    addCountry(country, num, countryNum++);
}

接下来，在getNumSubscriptionsInCountryForPeriod方法中，您必须以java方式比较字符串。不是==操作符而是equals()方法。您正在使用＆＃34; USA＆＃34;在数组和＆＃34;美国＆＃34;在您的测试中，您需要忽略大小写比较：equalsIgnoreCase()：

if ( country.equalsIgnoreCase((String)array[i][0])) {

接下来，您可以将方法修改为：

public double getNumSubscriptionsInCountryForPeriod(String country, int sYear, int eYear) {
    double sum = 0;

    for (int i = 1; i < array.length; i++) {

        if (country.equalsIgnoreCase((String) array[i][0])) {
            int start = 1 + sYear - year;
            int end = start + (eYear - sYear);

            if (start >= 0 && end < array[i].length) {

                for (int k = start; k <= end; k++) {
                    // System.out.println(">> " + country + " adding " + array[i][k]);
                    sum += (Double) array[i][k];
                }
            }
        }
    }

    return sum;
}

java中2d数组的总和

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