这是一条错误消息，在我尝试显示我的程序结果时不断出现。
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0
at AddressBookIO.getEntriesString(AddressBookIO.java:38)
at AddressBookEntryApp.main(AddressBookEntryApp.java:42)
我几乎可以肯定我的代码是正确的。除了显示我的结果之外，我的程序会执行它想要做的所有事情。 “”主“java.lang.ArrayIndexOutOfBoundsException：0”是令我困惑的部分。
下面是AddressBookIO.java和AddressBookEntryApp
的代码import java.io.*;
public class AddressBookIO
{
private static File addressBookFile = new File("address_book.txt");
private static final String FIELD_SEP = "\t";
private static final int COL_WIDTH = 20;
// use this method to return a string that displays
// all entries in the address_book.txt file
public static String getEntriesString()
{
BufferedReader in = null;
try
{
checkFile();
in = new BufferedReader(
new FileReader(addressBookFile));
// define the string and set a header
String entriesString = "";
entriesString = padWithSpaces("Name", COL_WIDTH)
+ padWithSpaces("Email", COL_WIDTH)
+ padWithSpaces("Phone", COL_WIDTH)
+ "\n";
entriesString += padWithSpaces("------------------", COL_WIDTH)
+ padWithSpaces("------------------", COL_WIDTH)
+ padWithSpaces("------------------", COL_WIDTH)
+ "\n";
// append each line in the file to the entriesString
String line = in.readLine();
while(line != null)
{
String[] columns = line.split(FIELD_SEP);
String name = columns[0];
String emailAddress = columns[1];
String phoneNumber = columns[2];
entriesString +=
padWithSpaces(name, COL_WIDTH) +
padWithSpaces(emailAddress, COL_WIDTH) +
padWithSpaces(phoneNumber, COL_WIDTH) +
"\n";
line = in.readLine();
}
return entriesString;
}
catch(IOException ioe)
{
ioe.printStackTrace();
return null;
}
finally
{
close(in);
}
}
// use this method to append an address book entry
// to the end of the address_book.txt file
public static boolean saveEntry(AddressBookEntry entry)
{
PrintWriter out = null;
try
{
checkFile();
// open output stream for appending
out = new PrintWriter(
new BufferedWriter(
new FileWriter(addressBookFile, true)));
// write all entry to the end of the file
out.print(entry.getName() + FIELD_SEP);
out.print(entry.getEmailAddress() + FIELD_SEP);
out.print(entry.getPhoneNumber() + FIELD_SEP);
out.println();
}
catch(IOException ioe)
{
ioe.printStackTrace();
return false;
}
finally
{
close(out);
}
return true;
}
// a private method that creates a blank file if the file doesn't already exist
private static void checkFile() throws IOException
{
// if the file doesn't exist, create it
if (!addressBookFile.exists())
addressBookFile.createNewFile();
}
// a private method that closes the I/O stream
private static void close(Closeable stream)
{
try
{
if (stream != null)
stream.close();
}
catch(IOException ioe)
{
ioe.printStackTrace();
}
}
// a private method that is used to set the width of a column
private static String padWithSpaces(String s, int length)
{
if (s.length() < length)
{
StringBuilder sb = new StringBuilder(s);
while(sb.length() < length)
{
sb.append(" ");
}
return sb.toString();
}
else
{
return s.substring(0, length);
}
}
}
和
import java.util.Scanner;
public class AddressBookEntryApp
{
public static void main(String args[])
{
// display a welcome message
System.out.println("Welcome to the Address Book application");
System.out.println();
Scanner sc = new Scanner(System.in);
int menuNumber = 0;
while (menuNumber != 3)
{
// display menu
System.out.println("1 - List entries");
System.out.println("2 - Add entry");
System.out.println("3 - Exit\n");
// get input from user
menuNumber = Validator.getIntWithinRange(sc, "Enter menu number: ", 0, 4);
System.out.println();
switch (menuNumber)
{
case 1:
{
String entriesString = AddressBookIO.getEntriesString();
System.out.println(entriesString);
break;
}
case 2:
{
// get data from user
String name = Validator.getRequiredString(sc, "Enter name: ");
String emailAddress = Validator.getRequiredString(sc, "Enter email address: ");
String phoneNumber = Validator.getRequiredString(sc, "Enter phone number: ");
// create AddressBookEntry object and fill with data
AddressBookEntry entry = new AddressBookEntry();
entry.setName(name);
entry.setEmailAddress(emailAddress);
entry.setPhoneNumber(phoneNumber);
AddressBookIO.saveEntry(entry);
System.out.println();
System.out.println("This entry has been saved.\n");
break;
}
case 3:
{
System.out.println("Goodbye.\n");
break;
}
}
}
}
}
答案 0 :(得分：1)
异常意味着您正在访问超出数组大小的数组元素。因此，您需要提供代码的详细信息，以便让您了解问题的原因。
答案 1 :(得分：1)
表示已使用非法索引访问数组。索引为负数或大于或等于数组的大小。
根据您的错误日志.. AddressBookIO.java中第38行的代码抛出此异常。
可以在这里..
String name = columns[0];
String emailAddress = columns[1];
String phoneNumber = columns[2];
如果0,1或2中没有元素..
答案 2 :(得分：1)
错误消息非常清楚：错误地访问了 no elements 的数组的第一个元素（索引0）。
线程“main”中的异常 java.lang.ArrayIndexOutOfBoundsException：[index is] 0
例如，这将抛出该异常：
int bad = (new int[0])[0]; // no elements :(
虽然以下是可以的：
int ok = (new int[1])[0]; // one element, can access it!
我怀疑是这样的：
String[] columns = line.split(FIELD_SEP); // empty array?
String name = columns[0]; // KABOOM!
在任何情况下，请检查异常中报告行上的代码。
在AddressBookIO.getEntriesString（ AddressBookIO.java:38 ）
答案 3 :(得分：1)
'address_book.txt'中的空行可能是？
答案 4 :(得分：1)
您正在尝试访问空数组的第一个元素。它不存在，因此您从运行时获得异常。
您尝试访问的数组是split()方法的结果。如果您传递一串分隔符，则只会返回一个空数组："\t"
因此，必须有一些行只包含它们之间没有任何内容的标签。
您应该考虑将正则表达式应用于每一行，而不是使用split()。这样，您可以同时验证行和应用“捕获组”的格式，以便轻松提取每个字段的值，即使它们是空字符串。
Pattern p = Pattern.compile("([^\t]*)\t([^\t]*)\t([^\t]*)");
...
Matcher m = p.matcher(line);
if (!m.matches()) {
/* The line is invalid; skip it or throw an exception. */
...
}
String name = m.group(1);
String emailAddress = m.group(2);
String phoneNumber = m.group(3);
答案 5 :(得分：0)
ArrayIndexOutOfBoundsException，该索引的大小超过指定数组的大小。
尝试改变这一点：
while(line != null)
{
String[] columns = line.split(FIELD_SEP);
String name = columns[0];
String emailAddress = columns[1];
String phoneNumber = columns[2];
entriesString += padWithSpaces(name, COL_WIDTH) +
padWithSpaces(emailAddress, COL_WIDTH) +
padWithSpaces(phoneNumber, COL_WIDTH) +
"\n";
line = in.readLine();
}
到此：
while(line != null)
{
String[] columns = line.split(FIELD_SEP);
if (columns.length > 2)
{
String name = columns[0];
String emailAddress = columns[1];
String phoneNumber = columns[2];
entriesString += padWithSpaces(name, COL_WIDTH) +
padWithSpaces(emailAddress, COL_WIDTH) +
padWithSpaces(phoneNumber, COL_WIDTH) +
"\n";
}
line = in.readLine();
}