我是一名新的Java学生，遇到了我正在撰写的一段代码的问题。我没有收到任何特定的错误消息，但是当我在菜单中选择一个选项时，它不会显示除每个项目的标题之外的任何内容。这是以前抛出空指针错误，但它们似乎已被纠正。
这是运行时出现的示例：
5 - Display Incomes by Category
6 - Exit
Enter Option (1 - 6):
5
Income Per Category:
Category Actual Income Pecentage of Income Achieved
这是代码：
package Java;
import java.util.Scanner;
import firstPrograms.My;
import firstPrograms.MyDate;
import firstPrograms.MyTime;
public class TestEvent
{
public static Scanner key = new Scanner(System.in);
public static void main(String[] args)
{
int noOfEvents = 25; // number of stipulated events
int option = 0;
Event [] allEvents = new Event [noOfEvents];
do
{
option = mainMenu(option);
switch (option)
{
case 1:
addEvents(allEvents, noOfEvents);
break;
case 2:
displayEvents(allEvents, noOfEvents);
break;
case 3:
//System.out.println("\nEnter Search criteria here");
do
{
option = searchMenu(option);
switch (option)
{
case 1:
//addEventsByEventNo(allEvents);
System.out.println("\nEnter Search criteria here");
break;
case 2:
//displayEventsByEventDate(allEvents);
System.out.println("\nEnter Search criteria here");
break;
case 3:
//displayEventsByEventCategory(allEvents);
System.out.println("\nEnter Search criteria here");
break;
case 4:
//displayIncomes(allEvents);
break;
//case 5:
// displayCategoryIncomes(allEvents);
//break;
//case 6:
//System.out.println("\nGoodbye");
}
}while (option != 4);
break;
case 4:
displayIncomes(allEvents);
break;
case 5:
displayCategoryIncomes(allEvents);
break;
case 6:
System.out.println("\nGoodbye");
}
}while (option != 6);
}
public int createArray(Event [] allEvents) // prepopulation of a certain amount of items into the array, leaving some space for additions
{
allEvents[0] = new Event (1000, "West Ham United v Arsenal", "Premiership", new MyDate (9, 03, 2016), new MyDate (9, 04, 2016), new MyTime (12, 45, 00), "Upton Park", 3500, 3498, 65.00, 0.025);
allEvents[1] = new Event (1001, "Sunderland v Arsenal", "Premiership", new MyDate (24, 03, 2016), new MyDate (24, 04, 2016), new MyTime (14, 05, 00), "Stadium of Light", 500, 500, 75.00, 0.05);
allEvents[2] = new Event (1002, "Arsenal v Crystal Palace", "Premiership", new MyDate (17, 03, 2016), new MyDate (17, 04, 2016), new MyTime (16, 05, 00), "Emirates Stadium", 100, 98, 125.00, 0.025);
allEvents[3] = new Event (1003,"Arsenal v West Bromwich Albion", "Premiership", new MyDate (21, 03, 2016), new MyDate (21, 04, 2016), new MyTime (19, 45, 00), "Emirates Stadium", 125, 72, 95.00, 0.025);
allEvents[4] = new Event (1004, "Arsenal v Norwich City", "Premiership", new MyDate (30, 03, 2016), new MyDate (30, 04, 2016), new MyTime (17, 30, 00), "Emirates Stadium", 1250, 1137, 110, 0.025);
allEvents[5] = new Event (1005, "Manchester City v Arsenal", "Premiership", new MyDate (8, 04, 2016), new MyDate (8, 05, 2016), new MyTime (16, 05, 00), "Etihad Stadium", 5000, 4796, 75.00, 0.05);
allEvents[6] = new Event (1006, "Arsenal v Aston Villa", "Premiership", new MyDate (15, 04, 2016), new MyDate (15, 05, 2016), new MyTime (19, 30, 00), "Emirates Stadium", 1250, 872, 16.00, 0.025);
allEvents[7] = new Event (1007, "MLS All-Stars v Arsenal", "Friendly", new MyDate (28, 01, 2016), new MyDate (28, 07, 2016), new MyTime (17, 00, 00), "Avaya Stadium", 500, 391, 75.00, 0.05);
allEvents[8] = new Event (1008, "Chivas de Guadalajara v Arsenal", "Friendly", new MyDate (31, 01, 2016), new MyDate (31, 07, 2016), new MyTime (19, 30, 00), "StubHub Center", 1250, 872, 16.00, 0.025);
allEvents[9] = new Event (1009, "West Ham United v Manchester United", "Cup", new MyDate (13, 03, 2016), new MyDate (13, 04, 2016), new MyTime (19, 00, 00), "Upton Park", 750, 615, 85.00, 0.075);
allEvents[10] = new Event (1010, "Everton v TBC (West Ham or Man United)", "Cup", new MyDate (14, 04, 2016), new MyDate (23, 04, 2016), new MyTime (17, 15, 00), "Wembley Stadium", 10000, 5000, 150.00, 0.015);
allEvents[11] = new Event (1011, "Crystal Palace v Watford", "Cup", new MyDate (24, 03, 2016), new MyDate (24, 04, 2016), new MyTime (16, 00, 00), "Wembley Stadium", 10000, 10000, 150.00, 0.015);
allEvents[12] = new Event (1012, "FA Cup Final - TBC", "Cup", new MyDate (25, 04, 2016), new MyDate (21, 05, 2016), new MyTime (15, 00, 00), "Wembley Stadium", 20000, 0, 150.00, 0.015);
allEvents[13] = new Event (1013, "UEFA Champions League Final - TBC", "Europe", new MyDate (5, 5, 2016), new MyDate (28, 05, 2016), new MyTime (19, 45, 00), "Stadio Giuseppe Meazza", 25000, 0, 350.00, 0.01);
allEvents[14] = new Event (1014, "UEFA Europa League Final - TBC", "Europe", new MyDate (6, 05, 2016), new MyDate (18, 05, 2016), new MyTime (19, 45, 00), "St. Jakob-Park", 20000, 0, 250.00, 0.015);
return 16;
}
public static int mainMenu(int option)
{
int tempOption = 0;
System.out.println("\n\nEvent Menu");
System.out.println("----------------------------");
System.out.println("1 - Add Event");
System.out.println("2 - Display All Events");
System.out.println("3 - Search Events");
System.out.println("4 - Display Incomes for Events");
System.out.println("5 - Display Incomes by Category");
System.out.println("6 - Exit");
System.out.println("Enter Option (1 - 6): ");
tempOption = key.nextInt();
key.nextLine();
return tempOption;
}
public static int searchMenu(int option)
{
int tempOption = 0;
System.out.println("\n\nEvent Menu");
System.out.println("----------------------------");
System.out.println("1 - Search By Event No");
System.out.println("2 - Search By Date");
System.out.println("3 - Search By Category");
//System.out.println("4 - Display Incomes for Events");
//System.out.println("5 - Display Incomes by Category");
System.out.println("4 - Previous Menu");
System.out.println("Enter Option (1 - 4): ");
tempOption = key.nextInt();
key.nextLine();
return tempOption;
}
public int option(int min, int max)
{
int input;
boolean valid;
do
{
valid = false;
input = key.nextInt();
if (input < min || input > max)
{
System.out.printf("\n\n%s%d%s%d%s", "Invalid input! Please re-enter a value between ", min, " and ", max, ": ");
}
else
{
valid = true;
//System.out.printf("\n\n%s%d%s%d%s%d", "Number entered ", input, " is between ", min, " & ", max);
}
} while (!valid);
return input;
}
private static void displayEvents(Event [] allEvents, int noOfEvents)
{
System.out.println("\nEvents:");
//for (int i = 0; i < allEvents.length; i++)
//{
//if(allEvents[i] != null)
//System.out.printf("\n\n\t" + allEvents.toString());
//}
int rowTotal = 0;
if(allEvents[rowTotal] != null)
{
do
{
System.out.println(allEvents[rowTotal].toString());
rowTotal++;
}while (rowTotal < allEvents.length);
}
}
private static void addEvents (Event[] allEvents, int noOfHours)
{
System.out.println("\nAdd Events:");
int day = 0, month = 0, year = 0;
MyDate tempSaleDate;
MyDate tempEventDate;
int hour = 0, mins = 0, secs = 0;
MyTime tempTime;
boolean answer = false;
String keyedAnswer = "";
for (int i = 0; i < allEvents.length; i++)
{
//Event[] newEvent = null;
//Event[] newEvent = new Event[allEvents.length] ;
//Event newEvent = allEvents[i + 1];
//newEvent[i] = new Event();
allEvents[i] = new Event();
//allEvents[i].setEventNo((allEvents[allEvents.length - 1]).getEventNo() + 1);
allEvents[i].setEventNo((allEvents[i].getEventNo() + 1));
System.out.println("\n\tPlease enter name of event: ");
allEvents[i].setEventName(key.nextLine());
System.out.println("\tPlease enter the event's category: ");
allEvents[i].setCategory(key.nextLine());
System.out.println("\tPlease enter event location: ");
allEvents[i].setVenue(key.nextLine());
System.out.println("\tPlease enter the event's tickets date of sale (ie 1 - 31): ");
day = key.nextInt();
System.out.println("\tPlease enter the event's tickets month of sale (ie 1 - 12): ");
month = key.nextInt();
System.out.println("\tPlease enter the event's tickets year of sale (ie 2016): ");
year = key.nextInt();
tempSaleDate = new MyDate(day, month, year);
allEvents[i].setDateOnSale(tempSaleDate);
key.nextLine();
System.out.println("\tPlease enter the event's date of event (ie 1 - 31): ");
day = key.nextInt();
System.out.println("\tPlease enter the event's month of event (ie 1 - 12): ");
month = key.nextInt();
System.out.println("\tPlease enter the event's year of event (ie 2016): ");
year = key.nextInt();
tempEventDate = new MyDate(day, month, year);
allEvents[i].setEventDate(tempEventDate);
key.nextLine();
System.out.println("\tPlease enter the event's start hour (ie 1am = 1, 10am = 10, 10pm = 22, etc): ");
hour = key.nextInt();
key.nextLine();
System.out.println("\tPlease enter the event's start minutes (ie = 00, 15, 30, 45, etc): ");
mins = key.nextInt();
key.nextLine();
tempTime = new MyTime(hour, mins, secs);
allEvents[i].setEventTime(tempTime);
System.out.println("\tPlease enter the event's ticket allocation: ");
allEvents[i].setTicketsReceived(key.nextInt());
key.nextLine();
System.out.println("\tPlease enter the amount of tickets sold for the event: ");
allEvents[i].setTicketsSold(key.nextInt());
key.nextLine();
System.out.println("\tPlease enter the event's ticket cost: £");
allEvents[i].setTicketCost(key.nextDouble());
key.nextLine();
System.out.println("\tPlease enter the event's ticket commission rate: ");
allEvents[i].setCommissionRate(key.nextDouble());
key.nextLine();
System.out.println("\n\t\tWould you like to add another event (Y / N): ");
keyedAnswer = key.nextLine();
//System.out.println("\n\tKeyed Answer = " + keyedAnswer);
if (answer = keyedAnswer.equalsIgnoreCase("N"))
{
answer = false;
break;
}
else
{
answer = true;
}
}
}
public static void displayIncomes(Event[] allEvents)
{
System.out.println("\n\nIncome per event");
System.out.println("\n\n\tEvent No" + "\t\tEvent" + "\t\t\t\tActual Income" + "\t\t\t\tPotential Income");
for (int i = 0; i < allEvents.length; i++)
{
if(allEvents[i] != null)
System.out.println("\n\n\t" + allEvents[i].getEventNo() + "\t\t" + allEvents[i].getEventName() + "\t\t\t£" + allEvents[i].getActualIncome() + "\t\t\t£" + allEvents[i].getPotentialIncome());
}
}
public static void displayCategoryIncomes(Event[] allEvents)
{
double tempActualIncome = 0.00, totalTemp = 0.00;
double percentageAchieved = 0.00;
String tempCategory;
System.out.println("\n\nIncome Per Category:");
System.out.println("\n\n\tCategory" + "\t\t\t\tActual Income" + "\t\t\tPecentage of Income Achieved");
for (int i = 0; i < allEvents.length; i++)
{
//if(allEvents[i] != null)
//{
//if (allEvents[i].getCategory() == "Premiership")
//if ("Premiership".equals(allEvents[i].getCategory()))
if (allEvents[i] != null && "Premiership".equals(allEvents[i].getCategory()))
{
//double tempActualIncome = 0.00;
//double percentageAchieved = 0.00;
//String tempCategory;
tempActualIncome = allEvents[i].getActualIncome();
totalTemp += tempActualIncome;
percentageAchieved = (tempActualIncome / allEvents[i].getPotentialIncome()) * 100;
tempCategory = "Premiership";
System.out.printf("%s%s%s%.2f%s%.2f", "\n\t", tempCategory, "\t\t\t\t£", totalTemp, "\t\t\t\t", percentageAchieved);
}
//else if (allEvents [i].getCategory() == "Friendly")
else if (allEvents[i] != null && "Friendly".equals(allEvents[i].getCategory()))
{
//double tempActualIncome = 0.00;
//double percentageAchieved = 0.00;
//String tempCategory;
tempActualIncome += allEvents[i].getActualIncome();
percentageAchieved = (tempActualIncome / allEvents[i].getPotentialIncome()) * 100;
tempCategory = "Friendly";
//System.out.println("\n\n\t" + tempCategory + "\t\t\t£" + tempActualIncome);
System.out.printf("%s%s%s%.2f%s%.2f", "\n\t", tempCategory, "\t\t\t\t£", tempActualIncome, "\t\t\t\t", percentageAchieved);
}
//else if (allEvents [i].getCategory() == "Cup")
else if (allEvents[i] != null && "Cup".equals(allEvents[i].getCategory()))
{
//double tempActualIncome = 0.00;
//double percentageAchieved = 0.00;
//String tempCategory;
tempActualIncome += allEvents[i].getActualIncome();
percentageAchieved = (tempActualIncome / allEvents[i].getPotentialIncome()) * 100;
tempCategory = "Cup";
System.out.println("\n\n\t" + tempCategory + "\t\t\t£" + tempActualIncome);
}
//else if (allEvents [i].getCategory() == "Europe")
else if (allEvents[i] != null && "Europe".equals(allEvents[i].getCategory()))
{
//double tempActualIncome = 0.00;
//double percentageAchieved = 0.00;
//String tempCategory;
tempActualIncome += allEvents[i].getActualIncome();
percentageAchieved = (tempActualIncome / allEvents[i].getPotentialIncome()) * 100;
tempCategory = "Europe";
System.out.println("\n\t" + tempCategory + "\t\t\t£" + tempActualIncome);
}
}
//}
//for (int i = 0; i < allEvents.length; i++)
//{
//System.out.println("\n\n\t" + allEvents[i].getCategory()+ "\t\t\t£" + allEvents[i].getActualIncome() + "\t\t\t£" + allEvents[i].getPotentialIncome());
//}
}
}
答案 0 :(得分：1)
先生，这是显而易见的事情，因为您的Event数组未初始化： 变化：
Event[] newEvent = null;
到
Event[] newEvent = new Event[allEvents.length] ;
另外我认为你应该在开始循环
之前做这个数组初始化代码答案 1 :(得分：0)