所以我已經(jīng)將代碼編寫到一個(gè)程序中，該程序應(yīng)該初始化來自不同位置的總計(jì)數(shù)據(jù)集并顯示它們。出于某種原因，我在第一個(gè) for 循環(huán)中不斷收到運(yùn)行時(shí)錯(cuò)誤，無法弄清楚原因。有人可以幫我弄清楚我做錯(cuò)了什么嗎？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]; } }}
2 回答
侃侃無極
TA貢獻(xiàn)2051條經(jīng)驗(yàn) 獲得超10個(gè)贊
您當(dāng)前的代碼有兩個(gè)問題：
1）變量沒有被初始化。為此，您可以Sales在方法中創(chuàng)建對(duì)象（從andmain中刪除靜態(tài)關(guān)鍵字）。calCityTotalcalMonthlyTotal
2）一旦上述問題得到解決，你會(huì)遇到Arrayindexoutofboundsexception因?yàn)閏itySum有長(zhǎng)度sales.length而你的循環(huán)calCityTotal進(jìn)入sales[0].length。
將變量聲明為static并在constructor. 靜態(tài)變量應(yīng)該獨(dú)立于任何實(shí)例。通讀Java：什么時(shí)候使用靜態(tài)方法才知道什么時(shí)候聲明靜態(tài)變量。如果要將變量聲明為static，則應(yīng)在static塊中初始化它們（Java 中的靜態(tài)塊）。
下面的代碼將起作用：
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];
}
}
}
}
翻過高山走不出你
TA貢獻(xiàn)1875條經(jīng)驗(yàn) 獲得超3個(gè)贊
你得到了NullPointerException因?yàn)閟ales在nullline for (row = 0; row < sales.length; row++)。
即使您sales在構(gòu)造函數(shù)中為變量設(shè)置了一個(gè)值Sales()，您也永遠(yuǎn)不會(huì)調(diào)用該構(gòu)造函數(shù)（如new Sales()）。
因此，要解決此問題，NullPointerException您可以在方法中調(diào)用Sales構(gòu)造函數(shù)，main()如下所示：
public static void main(String[] args)
{
new Sales();
calCityTotal();
calMonthlyTotal();
displayTable();
}
編輯
修復(fù)后NullPointerException，您的代碼仍然有一些其他問題。
在里面calCityTotal()，我認(rèn)為sales[0].length應(yīng)該更正。sales[row].length
citySum數(shù)組初始化為sales. 這意味著citySum.length等于“行”的數(shù)量。但是你寫citySum[col]了這會(huì)導(dǎo)致ArrayIndexOutOfBoundsException因?yàn)椤傲小钡臄?shù)量可以超過citySum.length. （這實(shí)際上發(fā)生在您的程序中。因?yàn)樾袛?shù) = 5，列數(shù) = 6。）
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