【发布时间】：2015-10-22 06:48:57
【问题描述】：
我对编程和 Java 完全陌生，所以请原谅任何愚蠢的错误和非常糟糕的代码（我不知道如何订购/格式化）。我的任务是制作具有三个功能的视频清单：列出、租用和检查。我有一个 ArrayList ，其中包含当前可用的视频清单。在检查功能下，我希望能够将返回日期字符串转换为日期，然后将其与今天的日期进行比较。如果返回日期和今天的日期相等，我想返回一条消息说：“视频今天到期”，如果返回日期已过（早于今天的日期），我想返回一条消息说“视频过期”。
我一直在研究如何将字符串转换为日期，反之亦然，并且整天都在尝试使用它以及更多尝试使其工作，但我似乎无法让它工作。我知道有很多类似的问题已经被询问和回答，但我已经尝试关注它们并且它不起作用。任何帮助将非常感激。正如我之前所说，我是一个完全的新手，所以请原谅任何愚蠢。
整个程序代码：
import java.text.DateFormat;
import java.text.ParseException;
import java.time.LocalDate;
import java.util.*;
class InventoryRow {
private String name;
private String type;
private Character availability;
private String returndate;
public InventoryRow(String name, String type, Character availability, String returndate) {
this.name = name;
this.type = type;
this.availability = availability;
this.returndate = returndate;
}
public String getReturndate() {
return returndate;
}
public void setReturndate(String returndate) {
this.returndate = returndate;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}
public Character getAvailability() {
return availability;
}
public void setAvailability(Character availability) {
this.availability = availability;
}
public String toString() {
return name + " " + type + " " + availability + " " + returndate;
}
}
public class InventorySort {
public static void main(String[] args) throws ParseException {
List<InventoryRow> videos = new ArrayList<InventoryRow>();
videos.add(new InventoryRow("Casablanca", "Old", 'Y', null));
videos.add(new InventoryRow("Jurassic Park", "Regular", 'N', "2015-07-30"));
videos.add(new InventoryRow("2012", "Regular", 'Y', null));
videos.add(new InventoryRow("Ant-Man", "New", 'Y', null));
LocalDate dateReturn = LocalDate.now().plusDays(3);
LocalDate dateToday = LocalDate.now();
Scanner input = new Scanner(System.in);
// Output the prompt
System.out.println("Do you want to list (l), rent (r) or check (c)?");
// Wait for the user to enter a line of text
String line = input.nextLine();
// List, rent and check functions
// List function
if (line.equals("l")) {
// //////////////////////////// Sort function
Collections.sort(videos, new Comparator<InventoryRow>() {
public int compare(InventoryRow o1, InventoryRow o2) {
return o1.getName().compareTo(o2.getName());
}
});
for (InventoryRow inventory : videos) {
System.out.println(inventory);
}
// /////////////////////////// Rent function
} else if (line.equals("r")) {
System.out.println("Which video would you like to rent?");
String line2 = input.nextLine();
// /////////////////////////// Search through ArrayList
boolean foundIt = false;
for (InventoryRow ir : videos) {
if (line2.equals(ir.getName()) && ir.getAvailability() == 'Y') {
foundIt = true;
break;
}
}
if (foundIt) {
System.out.println("Video available to rent! Would you like to rent this video?");
String line3 = input.nextLine();
if (line3.equals("Yes")) {
System.out.println("You have rented this video until " + dateReturn + ".");
for (InventoryRow ir : videos) {
if (ir != null && line2.equals(ir.getName())) {
ir.setAvailability('N');
ir.setReturndate(dateReturn.toString());
// //////////////// Just to test if this works
for (InventoryRow inventory : videos) {
System.out.println(inventory);
}
}
}
} else {
System.out.println("You have not rented this video.");
}
} else {
System.out.println("Video unavailable to rent.");
}
// /////////////////////////// Check function
} else if (line.equals("c")) {
System.out.println("Which video would you like to check is in the inventory?");
String line4 = input.nextLine();
// /////////////////////////// Search through ArrayList
boolean foundIt = false;
for (InventoryRow ir : videos) {
if (line4.equals(ir.getName())) {
foundIt = true;
break;
}
}
if (foundIt) {
System.out.println("Video found!");
for (InventoryRow ir : videos) {
LocalDate returnDate = LocalDate.parse(ir.getReturndate());
if (line4.equals(ir.getName()) && ir.getAvailability() == 'N' && returnDate.isEqual(dateToday)) {
System.out.println("Video due for return today.");
} else if (line4.equals(ir.getName()) && ir.getAvailability() == 'N'
&& returnDate.isBefore(dateToday)) {
System.out.println("Video is overdue!");
} else if (line4.equals(ir.getName()) && ir.getAvailability() == 'N') {
System.out.println("Video is due for return on: " + ir.getReturndate());
}
}
} else {
System.out.println("Video not found. Please see the inventory below.");
Collections.sort(videos, new Comparator<InventoryRow>() {
public int compare(InventoryRow o1, InventoryRow o2) {
return o1.getName().compareTo(o2.getName());
}
});
for (InventoryRow inventory : videos) {
System.out.println(inventory);
}
}
// /////////////////////////// If anything else is entered
} else {
System.out.println("The only options are to list (l), rent (r) or check (c).");
}
}
}
这是不工作的位，我不知道为什么：
if (foundIt) {
System.out.println("Video found!");
for (InventoryRow ir : videos) {
LocalDate returnDate = LocalDate.parse(ir.getReturndate());
if (line4.equals(ir.getName()) && ir.getAvailability() == 'N' && returnDate.isEqual(dateToday)) {
System.out.println("Video due for return today.");
} else if (line4.equals(ir.getName()) && ir.getAvailability() == 'N'
&& returnDate.isBefore(dateToday)) {
System.out.println("Video is overdue!");
} else if (line4.equals(ir.getName()) && ir.getAvailability() == 'N') {
System.out.println("Video is due for return on: " + ir.getReturndate());
}
}
这是我收到的错误消息：
Exception in thread "main" java.lang.NullPointerException: text
at java.util.Objects.requireNonNull(Objects.java:228)
at java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1846)
at java.time.LocalDate.parse(LocalDate.java:400)
at java.time.LocalDate.parse(LocalDate.java:385)
at InventorySort.main(InventorySort.java:141)
【问题讨论】：
-
“不工作” - 怎么样？您应该给出您尝试过的代码的简短 sn-ps，并告诉我们究竟是什么在其中不起作用。整个程序真的无关紧要。您只需要向我们提供显示您的问题的最少代码即可。两个注意事项：（1）最好从一开始就将数据保留为日期，而不是在搜索时转换它。在存储到列表之前输入数据并转换。 (2) 考虑使用 Java 8 的
LocalDate，而不是古老而有问题的Date。 -
感谢您告诉我。我添加了不起作用的代码并添加了我收到的错误消息。我还更改了代码以使用 LocalDate 而不是 Date。
标签： java string date arraylist calendar