我是在大学里第一次学习 Java。我正在努力打印工作。我无法打印，或者根本无法让程序打印任何内容。我认为问题出在显示方法上，但我无法解决它。因此，在下面的所有评论之后，我已经进行了更改，但是，我现在明白了，它只打印每个方法中的标题，并在我尝试向数组添加附加事件时给出以下错误。
添加活动：
线程“main”中的异常 java.lang.NullPointerException 在 JavaAssignment1.TestEvent.addEvents(TestEvent.java:207) 在 JavaAssignment1.TestEvent.main(TestEvent.java:28)
TestEvent.java：
package JavaAssignment1;
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;
int option = 0;
Event [] allEvents = new Event [25];
do
{
option = mainMenu(option);
switch (option)
{
case 1:
addEvents(allEvents);
break;
case 2:
displayEvents(allEvents);
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)
{
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("Event 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("Event 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)
{
System.out.println("\nEvents:");
for (int i = 0; i < allEvents.length; i++)
{
if(allEvents[i] != null)
System.out.printf("\n\n\t" + allEvents.toString());
}
}
private static void addEvents (Event[] allEvents)
{
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;
newEvent[i] = new Event();
allEvents[i].setEventNo((allEvents[allEvents.length - 1]).getEventNo() + 1);
System.out.println("\n\tPlease enter event name for 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 ("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 ("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 ("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\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());
//}
}
}
字符串与
equalsallEvents[i].getCategory() == "Premiership""Premiership".equals(allEvents[i].getCategory())
您使用了很多运行应用程序不必要的
staticmain==public static final String PERMSHIP = "Premiership";
并在代码中的任何地方使用它，但这是非常糟糕的做法。
使用“System.out.println”而不是System.out.printf
呃，你怎么能编译你的代码，这不起作用
Event [] allEvents = new Event [noOfEvents];
public static int createArray(Event [] allEvents){
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);
...
当你指定allEvents[0]时编译器不知道你是要修改this.allEvents[0]还是参数值
什么是
My.p(String value)
打印字符串是否有效
System.out.print(String valueToPrint)
或者
System.out.println(String valueToPrint)
第二个添加' ' 在要打印的字符串末尾
此处参数中的有用选项，您不会在函数中使用它
public static int mainMenu(int option)
{
int tempOption = 0;
My.p("\n\nEvent Menu");
My.p("\n----------------------------");
My.p("\n1 - Add Event");
My.p("\n2 - Display All Events");
My.p("\n3 - Search Events");
My.p("\n4 - Display Incomes for Events");
My.p("\n5 - Display Incomes by Category");
My.p("\n6 - Exit");
My.p("\nEnter Option (1 - 6): ");
tempOption = key.nextInt();
key.nextLine();
return tempOption;
}
allEvents [i].getCategory() == "Cup"最佳实践：
"Cup".equals(allEvents[i].getCategory())最后
for (int i = 0; i < allEvents.length(); i++)
{
//if(allEvents[i] != null)
System.out.printf("\n\n\t" + allEvents.toString());
}
我不喜欢 printf 更喜欢 print 或 println 但如果你想使用 printf 就这样做
System.out.printf("\n\n\t%s", allEvents.toString());