More About Handling Exceptions
This issue covers:
-More About Handling Exceptions
-Using HTML in Swing Components
These tips were developed using Java 2 SDK, Standard Edition, v 1.4.
This issue of the Core Java Technologies Tech Tips is written
Tutorial Details:
MORE ABOUT HANDLING EXCEPTIONS
The November 24, 2003 tip titled \"Handling Exceptions\" demonstrated some of the things that can go wrong if you ignore or mishandle exceptions. The following tip continues that discussion. Unfortunately, there were two errors in the final code example, FileAccess, of the previous tip. The errors appeared in the version of the tip that was sent to subscribers. The example was corrected after the mailing, and the corrected version appears on the Web site. The following tip actually starts with that faulty code. It shows you how to correct the problems in the code so that it handles exceptions more robustly. This tip also covers some of the components of the exception mechanism that were not introduced in the previous tip.
The following sample program, BadException, highlights three problems. Two of them appeared in the FileAccess sample program in the previous tip. The first of the two (Problem 1 in the code) is the more serious of the problems, and could result in an unanticipated exception being thrown. The second of the problems (Problem 2) is an unnecessary use of the exception mechanism. Problem 3, which did not appear in the previous tip, includes a resource leak and other items that require more explanation of the exception mechanism. Take a moment to consider what is wrong in each case and how you might fix it.
import java.io.FileReader;
import java.io.FileNotFoundException;
import java.io.File;
import java.io.BufferedReader;
import java.io.IOException;
public class BadException {
private static String fileName;
public static void main(String[] args) {
FileReader fileReader = null;
try {
fileReader = new FileReader(getFile(args));
} catch (FileNotFoundException e) {
System.out.println(
\"Could not locate a file: \" +
e.getMessage());
}
// problem 1: do not do the following
readFile(fileReader);
}
private static File getFile(String[] args)
throws FileNotFoundException {
// problem 2: do not do the following
try {
fileName = args[0];
} catch (ArrayIndexOutOfBoundsException e) {
throw new FileNotFoundException(
\"correct usage: \" +
\"java FileAccess \");
}
File aFile = new File(fileName);
if (aFile.exists()) {
return aFile;
} else {
throw new FileNotFoundException(
\"There is no file at \" + fileName);
}
}
private static void readFile(
FileReader fileReader) {
// problem 3: items not covered last time
BufferedReader buffReader =
new BufferedReader(fileReader);
String temp = \"\";
try {
System.out.println(
\"== Beginning of the file ==\");
while (
(temp = buffReader.readLine()) != null) {
System.out.println(temp);
}
} catch (IOException e) {
System.out.println(
\"There was a problem reading:\"
+ fileName);
}
System.out.println(
\"== End of the file ==\");
}
}
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