java - 获取数据集并将其打印在二维数组中

Question

所以我已经将代码编写到一个程序中，该程序应该初始化来自不同位置的总计数据集并按原样显示它们。由于某种原因，我在第一个 for 循环中不断收到运行时错误，但无法弄清楚原因。有人可以帮我弄清楚我做错了什么吗？

public class Sales {

private static String[] months;
private static String[] cities;
private static int[] citySum;
private static int[] monthlySum;
private static int[][] sales;
private static int col;
private static int row;


/**
 * @param args the command line arguments
 */
public static void main(String[] args) {

    calCityTotal();
    calMonthlyTotal();
    displayTable();

}

public Sales() {

    months = new String[] {"January","Febuary","March","April",
                           "May","June"};

    cities = new String[] {"Chilliwack","Kamloops","Kelowna",
                           "NanaimoSurrey","Vancouver","Victoria"};

    sales = new int[][] {{400,500,500,600,500,600},
                        {600,800,800,800,900,900},
                        {700,700,700,900,900,1000},
                        {500,600,700,800,700,700},
                        {900,900,900,1000,1100,1100}};

    citySum = new int[sales.length];

    monthlySum = new int[sales[0].length];
}

public static void calCityTotal() {

    for (row = 0; row < sales.length; row++){
        for (col = 0; col < sales[0].length; col++){
            citySum[col] += sales[row][col];
        }
    }
}

public static void calMonthlyTotal() {

    for (row = 0; row < sales.length; row++){
        for (col = 0; col < sales[0].length; col++){
            monthlySum[row] += sales[row][col];
        }
    }
}

Answer 1

您当前的代码有 2 个问题:

1) 变量未初始化。为此，您可以在 main 方法中创建 Sales 对象(从 calCityTotal 和 calMonthlyTotal 中删除 static 关键字)。

2) 解决上述问题后，您将遇到 ArrayindexoutofboundsException，因为 citySum 的长度为 sales.length，而 calCityTotal 中的循环转到 sales[0].length。

将变量声明为静态并在构造函数中初始化它们是没有意义的。静态变量应该独立于任何实例。浏览Java: when to use static methods知道何时声明静态变量。如果要将变量声明为 static，则应在 static block 中初始化它们( Static Block in Java )。

下面的代码可以工作:

public class Sales {

private String[] months;
private String[] cities;
private int[] citySum;
private int[] monthlySum;
private int[][] sales;
private int col;
private int row;


/**
 * @param args the command line arguments
 */
public static void main(String[] args) {
    Sales salesObj = new Sales();
    salesObj.calCityTotal();
    salesObj.calMonthlyTotal();

}

public Sales() {


    months = new String[]{"January", "Febuary", "March", "April",
            "May", "June"};

    cities = new String[]{"Chilliwack", "Kamloops", "Kelowna",
            "NanaimoSurrey", "Vancouver", "Victoria"};

    sales = new int[][]{{400, 500, 500, 600, 500, 600},
            {600, 800, 800, 800, 900, 900},
            {700, 700, 700, 900, 900, 1000},
            {500, 600, 700, 800, 700, 700},
            {900, 900, 900, 1000, 1100, 1100}};

    citySum = new int[sales.length+1];

    monthlySum = new int[sales[0].length];
}

public void calCityTotal() {

    for (row = 0; row < sales.length; row++) {
        for (col = 0; col < sales[0].length; col++) {
            citySum[col] += sales[row][col];
        }
    }
}

public void calMonthlyTotal() {

    for (row = 0; row < sales.length; row++) {
        for (col = 0; col < sales[0].length; col++) {
            monthlySum[row] += sales[row][col];
        }
    }
}

}